Zebra QLn420 troubleshooting guide: errors, faults and fixes

Short answer: According to Zebra, the Media Out icon flashes when the printer does not detect any media. Open the cover, place the roll between the media supports so that it turns freely, then close the cover until it latches: the alert clears once the media is loaded.

Likely cause

The QLn Series guide states that the Media Out icon flashes when there is no media in the printer and does not flash when media is present. The series alert table gives the full wording: MEDIA OUT on the first line, LOAD MEDIA on the second. The guide gives no other cause, but it asks you to keep the black mark and gap sensor windows clear.

Caution: Zebra asks you to switch the printer off before any cleaning, never to insert a pointed object into the printer and to take care with the tear bars, whose edges are very sharp.

What to do

1. Press the media cover button on the side of the printer: the cover opens by itself. Tilt it fully backwards.
2. Spread the media supports apart and place the roll between them, in the unwinding direction shown in the guide: the roll must turn freely.
3. Check the media width: Zebra specifies 50.8 to 111.76 mm for the QLn420.
4. Close the cover until it latches.
5. If the alert persists, switch the printer off, gently brush the inside and check that the black mark and gap sensor windows are free of dust (see calibration).

The two-line wording comes from the alert message table in the first edition of the guide (2011, QLn320 and QLn220); the current guide, which covers the QLn420, lists the QLn Series alerts and refers to an appendix that we were unable to read.

Sources: Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Loading Media Procedure (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Label Specifications (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: The printer detects that the media cover is open or not properly latched. Open the cover fully with its button, then close it firmly until it latches: according to Zebra, the alert clears as soon as the cause is corrected.

Likely cause

According to the QLn Series guide, the Head Latch icon appears, unlocked and flashing, when the media cover is open or not properly latched; it disappears when the cover is closed. The series alert table then shows MEDIA COVER OPEN followed by CLOSE MEDIA COVER. A cover that is not properly latched also appears in the troubleshooting table among the causes of media that does not feed and of partial printing.

What to do

1. Press the media cover button on the side of the printer to open it fully.
2. Check that the roll is properly held between the media supports (see loading the media).
3. Close the cover until it latches: the latch icon should disappear from the status bar.
4. If the alert is waiting for a response, press the soft key offered on the navigation bar to indicate that the action has been taken.

The Zebra guide describes no cause other than the cover being open or not properly latched. The two-line wording comes from the alert message table in the first edition of the guide (2011, QLn320 and QLn220); the current guide, which covers the QLn420, lists the QLn Series alerts and refers to an appendix that we were unable to read.

Sources: Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · LCD Control Panel Indicators (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Main Menu Screen (QLn320/220) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: According to Zebra, the error icon flashes when an error is present, other than media out and cover open, which have their own icons. Read the alert message displayed, correct the cause indicated, then respond with the soft key offered: the alert clears once the cause has been corrected.

Likely cause

QLn Series printers display alerts in plain text, for example “Media Out”, “Media Cover Open” or “Battery Low”. The Zebra guide specifies that the user can respond with a soft key to indicate that an action has been taken, and that the alert disappears once its cause has been dealt with. The series alert table gives a state (first line) and an action (second line) for each one.

What to do

1. Read both lines of the message: the first describes the state, the second the expected action (for example LOAD MEDIA or CHARGE BATTERY).
2. Look up the message in the lookup table and open the matching entry.
3. Correct the cause: loading the media, closing the cover, recharging the battery…
4. Respond to the alert with the soft key shown on the navigation bar.
5. For on-screen help, the QLn420 Tools menu (TOOLS) offers help topics on the media, the battery, the printhead and the error, latch and Bluetooth icons.

The current guide refers to an “Alert Messages” appendix that could not be read; the two-line wordings in this guide come from the same appendix in the first edition (2011, QLn320 and QLn220).

Sources: Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Main Menu Screen (QLn320/220) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Home Menu Screen (QLn420 and QLn Healthcare Printers) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: Zebra links skipped labels to three causes: media with no detectable black mark or gap, print area exceeded, black mark or gap sensor blocked or faulty. Check the media and the media type setting, clean the sensor windows, then check the calibration settings in the QLn420 menus.

Likely cause

The Zebra troubleshooting table (“Skip labels”) asks you to check that the media has a top-of-label mark or a gap between labels, that the maximum print area has not been exceeded and that the black mark or gap sensor is neither blocked nor faulty. The guide adds that if the maximum label length (Label length max) is set too short, the printer assumes it has continuous media and cannot calibrate.

Caution: Zebra asks you to switch the printer off before any cleaning and never to insert a pointed object into the printer.

Checks and settings specified by Zebra

1. Check the media: according to Zebra, reflective black marks must be centred on the roll, at least 12.7 mm wide and 3 to 11 mm long.
2. In the Settings menu (SETTINGS), select the media type that matches the loaded roll.
3. Still in SETTINGS, set the maximum label length (Label length max) to at least 25.4 mm more than the label length plus the gap between labels.
4. Switch the printer off, gently brush the inside and check that the black mark and gap sensor windows are free of dust.
5. The QLn420 Tools menu (TOOLS) offers a LABEL LENGTH CAL entry (label length calibration); the POWER UP ACTION and HEAD CLOSE ACTION settings can also trigger a calibration at power-up or when the printhead is closed.
6. Press the Feed button: according to Zebra, a label should feed up to the next gap or black mark.

When to call a technician: only change the label length calibration value in the SENSORS menu at the request of Zebra technical support or an authorised technician, as the guide requires.

The Zebra guide does not detail how calibration runs. It specifies that the label length calibration value in the Sensors menu (SENSORS) is set during sensor calibration.

Sources: Troubleshooting Topics (opens in a new window) · Appendix D – SETTINGS, TOOLS and SENSORS menus (opens in a new window) · Label Specifications (opens in a new window) · General Cleaning Instructions (opens in a new window) · Standard Control Panel (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: Press the cover button, spread the media supports apart and place the roll between them the right way round, then close the cover until it latches. The QLn420 accepts direct thermal media from 50.8 to 111.76 mm wide, in rolls with an outside diameter of 66.8 mm at most.

Likely cause

The QLn Series guide describes tool-free loading: the media supports adjust to the width of the roll and hold it. The QLn420 prints in direct thermal mode, without a ribbon: Zebra specifies Zebra direct thermal media, wound outside, with black mark or gap sensing, die-cut, continuous or linerless.

Caution: Zebra points out that the edges of the tear bars are very sharp.

Official loading procedure

1. Press the cover button on the side of the printer: the cover opens by itself. Tilt it fully backwards.
2. Spread the media supports apart and insert the roll between them, following the unwinding direction shown in the guide; the roll must turn freely.
3. Pull the start of the media out of the printer.
4. For use in tear-off mode, close the cover until it latches.
5. To peel labels one at a time, follow the peeler entry.
6. Check the format: width from 50.8 to 111.76 mm, label length from 12.7 to 812.8 mm, thickness from 0.061 to 0.190 mm, core of 19 mm or 35.05 mm minimum (35.05 mm minimum for linerless).

The guide states that the media feed length can be changed with an SGD (Set-Get-Do) command, described in the Zebra programming guide. It also points out that direct thermal prints gradually lose their legibility, especially at high temperatures.

Sources: Loading Media Procedure (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Label Specifications (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printing Technology (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Loading the Media (QLn420) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: According to Zebra, first check that the cover is closed and latched and that the roll turns freely on its supports. In peel-off mode, remove the last printed label. Finally, check that the label sensor is not blocked.

Likely cause

The Zebra troubleshooting table (“Media does not feed”) gives four causes: media cover not properly closed or latched, roll binding on its supports, last printed label not removed in peel-off mode, label sensor blocked.

Caution: Zebra asks you to switch the printer off before any cleaning, never to insert a pointed object into the printer and to take care with the tear bars, whose edges are very sharp.

What to do

1. Check that the media cover is closed and latched: the latch icon should not be displayed.
2. Open the cover and check that the roll turns freely between the media supports, without binding.
3. In peel-off mode, remove the last printed label.
4. Check that the label sensor is not blocked: switch the printer off and gently brush the inside.
5. Press the Feed button: a label should feed up to the next gap or black mark; continuous (journal) media feeds a length set by the software.

Sources: Troubleshooting Topics (opens in a new window) · Status Bar Icons (opens in a new window) · Standard Control Panel (opens in a new window) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: As Zebra specifies, open the head latch and the cover, remove the media and then reinstall it. If you use the peeler, remove any label left on its bar before disengaging it: otherwise, a jam may occur.

Likely cause

The Zebra troubleshooting table (“Label jam”) provides for opening the head latch and the media cover, then removing and reinstalling the media. The guide also points out that disengaging the peeler while peeled labels remain on its bar can cause a jam. On linerless models, the media can remain stuck to the platen roller (see linerless).

Caution: Zebra asks you never to insert a pointed or sharp object into the mechanism, and points out that the edges of the tear bars are very sharp.

What to do

1. Open the head latch and the media cover.
2. Remove the media, including any jammed labels.
3. Reinstall the roll (see loading the media) and close the cover until it latches.
4. Before disengaging the peeler, remove any label left on its bar.
5. Press Feed to check that the media feeds.

The PAPER JAM / REMOVE MEDIA wording comes from the alert table in the first edition of the guide (2011, QLn320 and QLn220).

Sources: Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Loading Media in Peel-off Mode (QLn420) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Cleaning the Printers (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: On linerless models, Zebra asks you to clean the printhead after each roll and to maintain the scraper and the inside every five rolls. If the media no longer comes away from the platen roller, an emergency cleaning with soapy water is provided for; if the jam continues, the roller must be replaced.

Likely cause

The Zebra guide provides for maintenance specific to linerless models: cleaning the printhead after each roll, cleaning the scraper with the adhesive side of the media and cleaning the inside with alcohol every five rolls. Media that no longer comes away from the platen roller calls for an emergency procedure.

Caution: Zebra specifies that cleaning with soapy water is an emergency procedure that reduces the service life of the platen roller. Switch the printer off before any cleaning and never insert a pointed object into it.

What to do

1. Switch the printer off.
2. Clean the printhead after each linerless roll (see printhead cleaning).
3. Clean the scraper with the adhesive side of the media, every five rolls or more often if necessary.
4. Clean the inside with 90% medical alcohol and a lint-free cotton swab, every five rolls or more often if necessary.
5. If the media no longer comes away from the platen roller, turn the roller and clean it with a lint-free cotton swab and a mixture of one part liquid soap to twenty-five parts water, then rinse with clean water. Do not use alcohol on the surface of a linerless roller.
6. Feed 1 to 2 metres of media to check the result.

When to call a technician: if the jam continues after this cleaning and 1 to 2 metres of media, Zebra asks you to replace the platen roller.

For linerless media, Zebra specifies a core of 35.05 mm minimum.

Sources: General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Cleaning the Printers (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Label Specifications (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: Zebra gives two causes: a dirty printhead and poor-quality media. Clean the printhead with a Zebra cleaning pen or a cotton swab moistened with 90% medical alcohol, from the centre outwards, then check the media. Zebra advises this cleaning every five rolls.

Likely cause

The Zebra troubleshooting table (“Poor or faded print”) asks you to clean the printhead and check the quality of the media. The QLn Series alert table also includes MAINTENANCE NEEDED / CLEAN PRINTHEAD. The darkness setting (Darkness) also matters: Zebra advises the lowest value that gives good quality.

Caution: Zebra warns that the printhead can be very hot after prolonged printing: let it cool down. Use only the cleaning products specified by Zebra, never insert a pointed object into the printer and take care with the very sharp edges of the tear bars.

Official printhead cleaning procedure

1. Switch the printer off and let the printhead cool down: it can be very hot after prolonged printing.
2. Open the media cover.
3. Wipe a Zebra cleaning pen, or a cotton swab moistened with 90% medical alcohol, over the thin grey line of the printhead, from the centre outwards.
4. Turn the platen roller and clean it with a lint-free cotton swab or a lint-free cloth lightly moistened with at least 90% medical alcohol (except for a linerless roller, see linerless).
5. Reload the media, close the cover and print a configuration report to check the result.
6. If the print is still faded, check the quality of the media and the Darkness setting in the SETTINGS menu; Zebra also states that a slower speed generally gives better quality.

Interval advised by Zebra: every five rolls (or more often if necessary) for the printhead and the platen roller, after each roll with linerless media. The quick start guide mentions 70% isopropyl alcohol for the roller; the user guide, 90% medical alcohol. The MAINTENANCE NEEDED wording comes from the alert table in the first edition of the guide (QLn320 and QLn220).

Sources: Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix D – SETTINGS menu (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Cleaning the Printers (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: Zebra gives three causes: misaligned media, a dirty printhead, a cover not properly closed or latched. Reload the roll correctly, clean the printhead, then close the cover until it latches.

Likely cause

The Zebra troubleshooting table (“Partial or missing print”) asks you to check the media alignment, clean the printhead and check that the cover is closed and latched. Regarding skipped labels, the same table asks you to check that the maximum print area of the label has not been exceeded: the QLn420 prints over a width of 104 mm at most.

Caution: Zebra asks you to switch the printer off before any cleaning, never to insert a pointed object into the printer and to take care with the tear bars, whose edges are very sharp.

What to do

1. Open the cover and check the alignment of the media between the media supports (see loading the media).
2. Clean the printhead (see printhead cleaning).
3. Close the cover until it latches.
4. Check in your software that the format exceeds neither the label size nor the print width of 104 mm.
5. Check the Print width and Left position settings in the SETTINGS menu.
6. Print a configuration report: its first line of criss-crossed “x” characters tests each element of the printhead.

Sources: Troubleshooting Topics (opens in a new window) · Printing Specifications (opens in a new window) · Appendix D – SETTINGS menu (opens in a new window) · Printing a Configuration Label (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: Print a configuration report: its first line, made up of criss-crossed “x” characters, tests each element of the printhead. To spare the printhead, Zebra advises the lowest darkness that gives good quality and cleaning every five rolls.

Likely cause

The QLn420 prints in direct thermal mode: each heated element of the printhead blackens the heat-sensitive media it touches. According to Zebra, darkness set too high can make the print blurred, hinder barcode reading and wear the printhead prematurely. Zebra quotes a printhead life of 2 million inches of media (about 50 km).

Caution: The printhead can be very hot after prolonged printing: Zebra asks you to let it cool down before cleaning it. Never insert a pointed object into the printer.

What to do

1. Print a configuration report and examine the first line of criss-crossed “x” characters.
2. Set Darkness, in the SETTINGS menu, to the lowest value that gives good quality.
3. Reduce the print speed if necessary: according to Zebra, a slower speed generally improves quality.
4. Clean the printhead every five rolls, or after each roll with linerless media (see printhead cleaning).
5. Use only the cleaning products specified by Zebra: the manufacturer accepts no liability for damage caused by other products.

The Zebra QLn Series guide describes neither an error message specific to the printhead nor a printhead replacement procedure.

Sources: Printing a Configuration Label (opens in a new window) · Printing Technology (opens in a new window) · Appendix D – SETTINGS menu (opens in a new window) · Printing Specifications (opens in a new window) · General Cleaning Instructions (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: First print a configuration report to check that the printer is working. If it is, Zebra asks you to check the baud rate, the cable, the radio link or network association, the battery and the label format sent.

Likely cause

The Zebra troubleshooting table (“No print”) gives: an incorrectly set serial baud rate, a battery that needs replacing, a faulty cable to the terminal, a lost radio link or wireless network association, and an invalid label format or command structure.

Caution: Zebra asks you to switch the printer off before connecting or disconnecting a communication cable.

What to do

1. Print a configuration report to check that the printer is working; if it does not print, first see the does not switch on and media does not feed entries.
2. With a serial connection, check that the printer's baud rate, shown on the configuration report and in the PORTS menu, matches that of the terminal.
3. Check the cable to the terminal, switching the printer off before connecting or disconnecting it.
4. For wireless, restore the Bluetooth link or the Wi-Fi network association (see Bluetooth and Wi-Fi).
5. Replace the battery if it is low or worn (see worn battery).
6. Check the label format sent; if in doubt, use the hexadecimal diagnostic mode (see communication diagnostics).

Sources: Troubleshooting Topics (opens in a new window) · Verify the Printer is Working (opens in a new window) · Cable Communication (opens in a new window) · Appendix D – PORTS menu (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: According to Zebra, garbled print comes from the baud rate of the serial connection. Set the same baud rate on the printer and on the terminal; if the communication errors continue, replace the cable.

Likely cause

The Zebra troubleshooting table links garbled print (“Garbled print”) to the communication baud rate, and communication errors (“Communication error”) to the baud rate and the cable to the terminal. The QLn420 RS-232 serial port accepts a baud rate of 9,600 to 115,200 baud, with configurable parity and data bits.

Caution: Zebra asks you to switch the printer off before connecting or disconnecting a communication cable.

What to do

1. Print a configuration report: it shows the printer's baud rate.
2. Compare with the terminal setting; the QLn420 PORTS menu also shows the baud rate, data bits, parity, stop bits and flow control (handshake).
3. Set both devices to the same values.
4. If the error persists, switch the printer off and replace the cable to the terminal.
5. To see what the printer is actually receiving, use the hexadecimal diagnostic mode (see communication diagnostics).

To save battery power, Zebra recommends using software flow control (XON/XOFF) where possible.

Sources: Troubleshooting Topics (opens in a new window) · Memory and Communications Specifications (opens in a new window) · Appendix D – PORTS menu (opens in a new window) · Extending Battery Life (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: Zebra provides a diagnostic mode (DUMP) that prints in hexadecimal everything the printer receives. Print a configuration report and press Feed within 3 seconds of the printed prompt, then send your label again. To exit, switch the printer off, wait 5 seconds and switch it back on.

Likely cause

The communications diagnostic mode is used when data does not pass correctly between the computer and the printer. The printer then prints the hexadecimal code of each piece of data received with its text equivalent (a full stop for non-printable characters) and saves a .dmp file, which can be viewed with Zebra Net Bridge.

Official diagnostic mode procedure

1. Print a configuration report.
2. At the end of the report, the printer prints Press FEED key to enter DUMP mode.
3. Press Feed within 3 seconds: the printer prints Entering DUMP mode. If you do not press it, it prints DUMP mode not entered and resumes normal operation.
4. Send the label that is causing the problem and compare the hexadecimal printout with the expected data.
5. On the QLn420, the TOOLS menu also offers a Diagnostic mode setting, which outputs all the data received in hexadecimal.
6. To exit the diagnostic mode, switch the printer off, wait 5 seconds, then switch it back on.

Sources: Communications Diagnostics (opens in a new window) · Appendix D – TOOLS menu (opens in a new window) · Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: Bring the device within about 10 metres and check in the BLUETOOTH menu that discovery (DISCOVERY) is active. With a Bluetooth 2.1 or later device, pairing uses Secure Simple Pairing: with numeric comparison, check that the six-digit number is identical on both devices.

Likely cause

The QLn420 behaves as a peripheral: it is the terminal that initiates the connection. If the printer is not discoverable, the terminal can only pair with it if it already knows its Bluetooth address (BDADDR) or has already been paired with it. Zebra specifies a range of about 10 metres; the minimum security setting sets the lowest level accepted by the printer, and pairings are stored (bonding), even after switching off.

What to do

1. Watch the Bluetooth icon in the status bar: solid, the link is established; flashing, the printer is connecting or receiving data; absent, the link is inactive.
2. In the QLn420 BLUETOOTH menu, check that DISCOVERY is set to ON and note the minimum security mode (MIN SECURITY MODE).
3. Bring the terminal within about 10 metres.
4. If the printer is not discoverable, pair it using its Bluetooth address (BDADDR), printed as a barcode on the back of the printer.
5. With a Bluetooth 2.1 or later device, pairing uses Secure Simple Pairing; according to Zebra, the PIN code is only used with Bluetooth 2.0 or older devices.
6. If an old pairing is causing problems, the SGD command bluetooth.clear_bonding_cache clears the pairings stored by the printer; Zebra compares it to “forget this device” on the terminal side.
7. To change the Bluetooth name, visibility or security mode, use Zebra Setup Utilities (ZSU), with the printer connected via USB.
8. For an iPhone or iPad (iOS 5 or later), only printers whose part number has an “M” in ninth position (Made for iPhone) are compatible.

The QLn Series guide also describes pairing via NFC (Print Touch icon), but the QLn420 diagram does not show a Print Touch icon: check whether there is one on the side of your printer. If there is, Zebra asks you to place the smartphone within 7.62 cm of the icon.

Sources: Wireless Communications with Bluetooth (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Bluetooth Networking Overview (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix D – BLUETOOTH menu (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Made for iPhone (MFi) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Near Field Communication (NFC) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Wireless Configuration for 802.11n and Bluetooth Radios for Link-OS Mobile Printers (opens in a new window) – Wireless Configuration for 802.11n and Bluetooth Radios for Link-OS Mobile Printers (P1048352-001 Rev. C) (official documentation).

Short answer: The printer has lost the Wi-Fi access point signal. Move it closer to an access point: the SIGNAL RESTORED message signals that the signal is back. If the printer never associates, check the network name (ESSID) and the security mode with Zebra Setup Utilities and your network administrator.

Likely cause

The QLn Series alert table reserves LOSS OF SIGNAL / MOVE IN RANGE OF AP and SIGNAL RESTORED for 802.11 models. The WLAN icon in the status bar shows the stage reached: antenna flashing without brackets, searching for an access point; one solid bracket, printer associated and authenticating; two solid brackets, connected. The bars show the signal strength (zero bars: no signal).

Caution: According to Zebra, Wi-Fi printers are only approved in certain countries. Outside the United States and Japan, set the country of use: operating outside the permitted power and frequency limits may breach local regulations.

What to do

1. Move the printer closer to an access point and watch the WLAN icon and its signal bars (four bars: more than 75%).
2. In the QLn420 NETWORK menu, check the WLAN status (WLAN STATUS), the IP address, the ESSID, the channel and the signal strength.
3. If the icon stays on a single bracket (authentication), check the security mode and the credentials with your network administrator.
4. To reconfigure Wi-Fi, connect the printer to the PC via USB, open Zebra Setup Utilities, choose Configure Printer Connectivity, then enter the IP addressing (DHCP or fixed), the radio type, the country, the ESSID and the security mode. ZSU sends the commands and the printer restarts.
5. If the QLn420 is sitting on its Ethernet cradle with an active link, its Wi-Fi radio is switched off: see Ethernet cradle.

QLn Series Wi-Fi printers bear the words “Wireless Network Printer” on the serial number label on the back. The wlan.power_save power-saving setting (enabled by default) affects the radio's power consumption; Zebra explains how to view it and disable it with an SGD command from ZSU. The LOSS OF SIGNAL wording comes from the alert table in the first edition of the guide (QLn320 and QLn220).

Sources: Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · WLAN Overview (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix D – NETWORK menu (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) · Wireless Configuration for 802.11n and Bluetooth Radios for Link-OS Mobile Printers (opens in a new window) – Wireless Configuration for 802.11n and Bluetooth Radios for Link-OS Mobile Printers (P1048352-001 Rev. C) (official documentation).

Short answer: This is the operation Zebra intends: on a QLn fitted with Wi-Fi, the 802.11 radio switches off as long as the cradle's Ethernet link is active, and switches back on when it becomes inactive. Bluetooth, USB and the serial port remain active on the cradle.

Likely cause

Only printers with the Ethernet option connect to the network on the QLn420-EC cradle; the PCC code on the back of the printer indicates this (a code of the type QNx-xxxxx0xx-xx does not support Ethernet). When the printer detects the cradle power supply and an active Ethernet link, it restarts automatically and connects to the network.

What to do

1. Check that your QLn420 has the Ethernet option: PCC code on the back of the printer, or the display menus, which indicate options that are not installed.
2. Before placing it on the cradle for the first time, remove the plastic cover from the docking contacts, held by two screws under the QLn420.
3. Place the printer on the cradle: it switches on automatically. The cradle's power light should be solid green.
4. With an active network link, wait for the automatic restart: the Ethernet icon is displayed solid once connected and flashes while receiving data.
5. To get Wi-Fi back, remove the printer from the cradle or unplug the network cable: the 802.11 radio switches back on when the Ethernet link becomes inactive.
6. On the cradle, do not use the printer's power socket: connect the AC adapter directly to the cradle.

The QLn420-EC cradle also recharges the battery and serves as an auxiliary power supply; when docked, the printer remains usable (display, buttons, printing, changing media).

Sources: Ethernet and Charging Cradles (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printer Operation with Cradle (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Single Bay (QLn420-EC for QLn420 Only) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: Check that the peeler lever is locked in the up position after loading, and that your labels are not synthetic: according to Zebra, the peeler works poorly with most synthetic labels. Before disengaging the peeler, remove any label left on its bar.

Likely cause

Zebra states that the peeler works poorly with most synthetic labels, which are more flexible and tend to stay stuck to their liner; the QLn420 can nevertheless print on these labels. A peeled label left on the bar when the peeler is disengaged can cause a jam. With the peeler, the print speed drops from 4 to 2 inches per second.

Caution: Zebra asks you never to insert a pointed object into the mechanism; the edges of the tear bars are very sharp.

Official loading procedure for peel-off mode

1. Remove a few labels from the start of the roll, then load the media (see loading the media).
2. Close the media cover.
3. Raise the peeler lever, on the side of the printer below the cover button, and lock it in the up position to fully engage the peel bar.
4. Switch the printer on, or press Feed if it is already on: the media feeds to the next label.
5. Remove each printed label: the Zebra troubleshooting table lists a last label not removed as a cause of media not feeding.
6. To disengage the peeler, first remove any labels left on the bar, then press the release button while pushing the lever down.
7. Clean the peeler bar with a Zebra cleaning pen if necessary.

Sources: Loading Media in Peel-off Mode (QLn420) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printing Specifications (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Loading the Media in QLn420 (Peeler Activated) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Cleaning the Printers (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: Check that the battery is properly clicked into place, then recharge or replace it. A new battery is supplied in sleep mode: connect the AC adapter or place it in a Zebra charger to wake it up. To switch the QLn420 on, hold down the Power button for 1.5 to 2.5 seconds.

Likely cause

The Zebra troubleshooting table (“No power”) gives a battery that is incorrectly installed, discharged or needs replacing. Batteries are supplied in sleep mode to preserve their capacity. If the control panel lights up briefly and then goes off when the battery is installed, the battery is not fully charged.

Caution: Zebra instructions: avoid any short-circuit of the battery terminals (risk of burns, injury or fire); do not incinerate it, do not disassemble it and do not expose it to more than 65 °C (60 °C according to the quick start guide). Use only chargers approved by Zebra and dispose of used batteries properly.

What to do

1. Rotate the belt clip if it is in the way, then insert the battery into its compartment under the printer, tilting it until it latches; it cannot be fitted the wrong way round.
2. If the battery is new, wake it up: connect the AC adapter or place it in a Smart Charger-2 or quad charger.
3. Recharge the battery (see charging the battery).
4. Hold down the Power button for 1.5 to 2.5 seconds and release it when the display lights up; start-up takes about 10 seconds.
5. If the printer still does not start, try a charged Zebra battery: according to Zebra, QLn printers only work correctly with genuine Zebra smart batteries.
6. If the display lights up but stays blank, see blank display.

Sources: Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Installing the Battery (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Standard Control Panel (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Smart Battery (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Battery Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Battery Install & Charging (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: The battery is almost empty: according to Zebra, the battery icon no longer shows any bars at 20% charge or less. Recharge it with the AC adapter, the cradle or a Zebra charger, or replace it with a charged battery.

Likely cause

The QLn420 displays the “Battery Low” alert when the charge becomes too low; the series alert table completes it with CHARGE BATTERY. The battery icon shows the level: four bars above 80%, three from 60 to 80%, two from 40 to 60%, one from 20 to 40%, none at 20% or less.

Caution: Zebra asks you to charge the battery between 0 and 40 °C, out of the sun, with a Zebra charger designed for lithium-ion batteries.

What to do

1. Connect the AC adapter to the printer's charging socket, or place the printer on its cradle: charging takes place whether the printer is on or off.
2. Check that the charge light turns solid yellow (charging in progress), then solid green (charging complete).
3. You can print while charging, but Zebra specifies that charging then takes longer.
4. Zebra also suggests having a spare battery available.
5. If the alert comes back quickly after a full charge, see worn battery and operating time.

The second-line wording comes from the alert table in the first edition of the guide (QLn320 and QLn220).

Sources: Main Menu Screen (QLn320/220) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · AC Power Adapter (p/n P1031365-024) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Extending Battery Life (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: Connect the Zebra AC adapter to the printer's charging socket or place the printer on its QLn420-EC cradle. The charge light is solid yellow during charging and solid green when the battery is full. Charge between 0 and 40 °C.

Likely cause

Zebra offers four ways of charging the QLn420: the AC adapter (kit P1031365-024) and the QLn420-EC Ethernet cradle, with the battery in the printer, and the Smart Charger-2 (SC2) single charger and the UCLI72-4 quad charger, with the battery removed. The printer's charge light only comes on when a DC power supply is connected.

Caution: According to Zebra, use only chargers approved by Zebra: other chargers may damage the battery or the printer and void the warranty. Do not charge in direct sunlight or above 40 °C, and do not place any charger where liquids or metal objects could fall into the charging bays.

Official procedure with the AC adapter

1. Open the protective cover to access the printer's DC input socket.
2. Attach the mains cord for your country to the adapter and plug it into a socket.
3. Connect the adapter plug to the charging socket: the printer switches on and charging starts; it continues whether the printer stays on or is switched off.
4. Watch the light: solid yellow, charging in progress; solid green, charging complete.
5. In the quad charger, allow less than 3 hours to fully charge an empty standard battery (less than 2 hours for 80%), and less than 5 hours for an extended battery.
6. Remove the battery if the printer is not going to be used for a day or more, unless it is on maintenance charge.

When sitting on its cradle, the printer cannot take the AC adapter in its own socket: connect it to the cradle instead.

Sources: AC Power Adapter (p/n P1031365-024) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Standard Control Panel (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Model UCLI72-4 Quad Charger (AC18177-5) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Charger Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Battery Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Extending Battery Life (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printer Operation with Cradle (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Battery Install & Charging (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: According to Zebra, a charge light that is off while the adapter is connected signals a charging fault. Check the temperature (charging between 0 and 40 °C), use the genuine Zebra adapter and let the battery return to room temperature before trying again. If the fault persists, replace the battery.

Likely cause

The QLn Series distinguishes several alerts: charging temperature fault (battery too hot or too cold, charging to be done between 0 and 40 °C), charging fault and failed battery, the last two requiring the battery to be replaced. Zebra specifies that the battery only charges with the 12 V DC supplied by the Zebra AC adapter.

Caution: Zebra instructions: avoid any short-circuit of the battery terminals (risk of burns, injury or fire); do not incinerate it, do not disassemble it and do not expose it to more than 65 °C (60 °C according to the quick start guide). Use only chargers approved by Zebra and dispose of used batteries properly.

What to do

1. Check that the Zebra AC adapter is properly connected to the socket and to the printer, or to the cradle if the printer is sitting on it.
2. If the CHARGING TEMP FAULT message is displayed, place the printer somewhere between 0 and 40 °C, out of the sun, and wait for the battery to return to room temperature.
3. Restart charging and watch the light: solid yellow, charging has resumed.
4. To isolate the cause, try charging the battery in an external Zebra charger (see charger lights).
5. If CHARGING FAULT or BATTERY FAILED is displayed, replace the battery with a genuine Zebra smart battery.

The exact alert wordings come from the alert table in the first edition of the guide (QLn320 and QLn220), which specifies that CHARGING TEMP FAULT covers a battery that is too hot as well as too cold. The current guide adds that the printer's power socket is protected up to 36 V; above that, the input fuse opens permanently to limit the risk of fire.

Sources: Standard Control Panel (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printer Operation with Cradle (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Smart Battery (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Battery Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Extending Battery Life (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printer Controls (QLn420) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) (official documentation).

Short answer: The smart battery counts its charge cycles and signals its wear. From 300 cycles, the QLn420 advises replacing it; beyond 600 cycles, it displays “Replace Battery Shutting Down” and switches off after 30 seconds. Replace the battery with a genuine Zebra smart battery.

Likely cause

According to Zebra, the battery electronics track, among other things, the number of cycles and the date of manufacture. The state of health goes from GOOD (fewer than 300 cycles, no message) to REPLACE (300 to 550 cycles: “Battery Diminished Consider Replacing”; 550 to 600 cycles: “Warning-Battery Is Past Useful Life”, with one long beep), then to POOR (more than 600 cycles: “Replace Battery Shutting Down” flashes with one beep per second and the printer switches off after 30 seconds).

Caution: Zebra asks you to dispose of used batteries properly; do not incinerate them, do not disassemble them and do not short-circuit them.

What to do

1. Open the QLn420 BATTERY menu: it shows the state of health (HEALTH), the number of cycles (CYCLE COUNT), the date of first use (FIRST USED) and the voltage.
2. If the battery is more than a year old, Zebra states that reduced operating time may be due to normal ageing.
3. On the Smart Charger-2, the health light confirms the state: green, good; yellow, reduced capacity; flashing yellow, end of useful life; amber, unusable battery to be replaced.
4. Switch the printer off before removing the battery: Zebra recommends this to limit the risk of corruption.
5. Replace the battery with a genuine Zebra smart battery: according to Zebra, QLn printers only work correctly with these.
6. Dispose of the used battery in accordance with recycling rules.

Sources: Smart Battery (opens in a new window) · Battery Health Indicator (opens in a new window) · Troubleshooting Topics (opens in a new window) · Appendix D – BATTERY menu (opens in a new window) · Printing Technology (opens in a new window) · Battery Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: On the quad charger, a flashing amber light signals a battery fault; according to Zebra, the charger may also show it if the battery is too hot or too cold to charge. Let it return to room temperature and restart charging; if the amber light flashes again, Zebra asks you to dispose of the battery.

Likely cause

The UCLI72-4 quad charger charges up to four QLn batteries removed from the printer. Its lights indicate: amber solid and green off, charging in progress; amber solid and green flashing, 80% reached (battery usable); amber off and green solid, fully charged; amber flashing and green off, fault (battery to be replaced). The charger stops charging after six hours, whatever level has been reached.

Caution: Zebra asks you not to block the charger's ventilation slots, to plug it into a socket that is not likely to be switched off for overnight charging, and not to place any charger where liquids or metal objects could fall into the bays.

What to do

1. Check that the power light on the front of the charger is on.
2. Insert the battery until it stops, then tilt it until it clicks: the amber light under the battery comes on if it is correctly in place.
3. If there is a fault, remove the battery, let it return to room temperature and restart charging.
4. If the amber light flashes again on the second attempt, dispose of the battery in accordance with the disposal instructions.
5. If the battery is not full after the six-hour cut-off, Zebra states that it may need to be replaced.
6. On the Smart Charger-2, an amber charge light also signals a fault; its health light shows wear (see worn battery).

Sources: Model UCLI72-4 Quad Charger (AC18177-5) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Charging Status Indicators (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Charger Safety (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · UCLI72-4 Quad Charger (All QLn Series Printers) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) · Smart Charger-2 (SC2) Single Battery Charger (All QLn Series Printers) (opens in a new window) – Quick Start Guide QLn Series Mobile Printers (P1031679-002 Rev. B) (official documentation).

Short answer: Zebra advises charging out of the sun and below 40 °C, setting the darkness and speed only as high as necessary, limiting the display backlight and removing the battery if the printer is not used for a day or more. A battery more than a year old may also simply have aged.

Likely cause

The Zebra guide groups its advice under “Extending Battery Life”: charging conditions, charger, choice of media, print settings and storage. It points out that rechargeable batteries gradually lose their capacity and can only withstand a limited number of recharges.

Caution: According to Zebra, only a Zebra charger designed for lithium-ion batteries should be used: other chargers may damage the battery. Dispose of batteries properly at the end of their life.

Zebra's advice

1. Charge out of the sun and away from high temperatures (40 °C at most), with a Zebra charger designed for lithium-ion batteries.
2. Choose media suited to your application; if the same text or logo appears on every label, consider pre-printed labels.
3. Set the darkness and print speed as precisely as possible for your media.
4. Use software flow control (XON/XOFF) where possible.
5. Adjust the backlight in the TOOLS menu (LCD BACKLIGHT, BACKLIGHT TIMEOUT): according to Zebra, heavy use of the backlight reduces the operating time between charges.
6. Remove the battery if the printer is not used for a day or more, unless it is on maintenance charge.
7. Check the battery's state of health (see worn battery) and have a spare battery available.

Sources: Extending Battery Life (opens in a new window) · Programmable LCD Settings (opens in a new window) · Appendix D – TOOLS menu (opens in a new window) · Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: The QLn420 uses the Windows Open HCI USB interface driver, and the USB drivers are included in the Zebra ZDesigner driver. Install the ZDesigner v10 driver recommended by Zebra, or the Windows v5 driver if you use the CPCL or EPL languages, then connect the cable with the printer switched off.

Likely cause

According to the Zebra guide, the printer connects via a USB 2.0 cable with a small keyed 5-pin connector; other terminals may require specific USB drivers. The Zebra support page for the QLn420 offers the ZDesigner v10 driver (version 10.5.1.27605, recommended), the Windows v5 driver (5.1.17.7414, for CPCL or EPL) and Zebra Setup Utilities (v1.1.9.1325).

Caution: Zebra asks you to switch the printer off before connecting or disconnecting a communication cable.

What to do

1. Download the driver from the Zebra support page for the QLn420: ZDesigner v10 (recommended) or Windows v5 driver for CPCL and EPL.
2. Install it, or use Zebra Setup Utilities, which Zebra presents as the recommended installation and configuration utility.
3. Switch the printer off, then connect the USB cable: the connector is keyed, do not force it.
4. Switch the printer back on; the Data icon flashes when data passes through the USB or serial port.
5. For a permanent connection, lock the cable with the retaining cap by turning it clockwise.
6. With a non-Windows terminal, Zebra states that specific USB drivers may be required.

For macOS and Linux, the Zebra support page refers to information on the CUPS driver, a third-party driver.

Sources: USB Communications (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Cable Communication (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Providing Strain Relief for Communications Cable (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Status Bar Icons (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · QLn420 Mobile Printer Support – Zebra support page for the QLn420 (link removed on 21 October 2026: the page is no longer available at its former address) (official documentation).

Short answer: The latest firmware published by Zebra for the QLn420 is V68.20.15Z (Link-OS v5.2, 15 October 2018). It is installed with the Zebra ZDownloader utility. While it is being written, do not switch the printer off and do not remove the battery.

Likely cause

The Zebra support page offers the file V68.20.15Z.zip (Link-OS v5.2 for QLn220, QLn320, QLn420, QLn220-HC and QLn320-HC) and the ZDownloader utility, which loads the printer's operating system (firmware) and service packs. The QLn Series alert table lists the messages displayed during a download, including RETRIEVING FIRMWARE / DO NOT POWER OFF!.

Caution: Do not switch the printer off during an update (DO NOT POWER OFF!). Zebra also recommends switching the printer off before removing the battery, to limit the risk of corruption.

What to do

1. Note the current version: it appears on the QLn420 home screen and on the configuration report.
2. Download V68.20.15Z.zip and ZDownloader from the Zebra support page for the QLn420.
3. Send the firmware to the printer with ZDownloader.
4. Let the printer display DOWNLOADING FIRMWARE and then FIRMWARE WRITING TO FLASH without switching it off.
5. If the display stays blank after the operation, Zebra states that a missing or corrupted application must be reloaded (see blank display).

Zebra has withdrawn the QLn420 from sale and states that its customer support ended on 30 June 2025 in the EMEA region (31 December 2025 in North America, Latin America and Asia-Pacific); the resources remain online but are no longer updated. The update messages come from the alert table in the first edition of the guide (QLn320 and QLn220); some lines in this table concern the Mirror function, available only on printers fitted with 802.11 Wi-Fi or Ethernet.

Sources: QLn420 Mobile Printer Support – Zebra support page for the QLn420 (link removed on 21 October 2026: the page is no longer available at its former address) · Appendix G – Alert Messages (opens in a new window) – Zebra QLn Mobile Printers Series User Guide, 1st edition (P1028026-002 Rev. A, April 2011, QLn320 and QLn220) · Home Menu Screen (QLn420 and QLn Healthcare Printers) (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Printing Technology (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Troubleshooting Topics (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).

Short answer: With the printer switched off and continuous media (journal, without black marks) loaded, hold down the Feed button, press and release the Power button, and release Feed as soon as printing starts. On the QLn420, the report can also be printed from the TOOLS menu.

Likely cause

Zebra asks you to print this report before connecting the printer, to check that it is working. It starts with a line of criss-crossed “x” characters that tests each element of the printhead, then shows the software version, the model, the serial number, the serial baud rate, the network and Ethernet settings, the installed peripherals, the memory, the maximum label size, the fonts and the files in memory.

Official procedure (two-key method)

1. Switch the printer off and load continuous media (journal), without black marks on the back.
2. Hold down the Feed button.
3. Press and release the Power button, keeping Feed held down.
4. Release Feed as soon as printing starts.
5. On the QLn420, you can also use the TOOLS menu, PRINT INFORMATION option, which prints the configuration report, the sensor profile and the network settings, among other things.

When to call a technician: if the report does not print or if the problem is not covered by the guide, Zebra refers you to its technical support, with the model, the serial number (label on the back and report) and the PCC code of the printer.

Zebra states that customer support for the QLn420 has no longer been provided since 30 June 2025 in the EMEA region.

Sources: Printing a Configuration Label (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Verify the Printer is Working (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Appendix D – TOOLS menu (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · Troubleshooting Tests (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) · QLn420 Mobile Printer Support – Zebra support page for the QLn420 (link removed on 21 October 2026: the page is no longer available at its former address) (official documentation).

Short answer: First check that the printer is switched on. If the display stays blank, Zebra states that the printer application is missing or corrupted and must be reloaded. A display that dims after a few seconds may correspond to the backlight timeout, which can be set in the TOOLS menu.

Likely cause

The Zebra troubleshooting table (“Blank LCD screen”) gives two causes: printer switched off, or application missing or corrupted, to be reloaded. In addition, the QLn420 TOOLS menu lets you switch the backlight on or off (LCD BACKLIGHT), set its timeout (BACKLIGHT TIMEOUT) and adjust the display contrast (LCD CONTRAST).

What to do

1. Switch the printer on: hold down the Power button for 1.5 to 2.5 seconds, until the display lights up (see does not switch on).
2. If the display is on but hard to read, adjust the contrast (LCD CONTRAST) and the backlight in the TOOLS menu.
3. If the display dims too quickly, increase the BACKLIGHT TIMEOUT delay; Zebra points out that heavy use of the backlight reduces the operating time.
4. If the display stays blank while the printer is switched on, reload the printer application (firmware) (see firmware).

For the QLn320 and QLn220, Zebra describes a low-power mode in which the backlight goes off after 5 to 1,200 seconds of inactivity (10 seconds by default); the guide does not explicitly describe it for the QLn420.

Sources: Troubleshooting Topics (opens in a new window) · Appendix D – TOOLS menu (opens in a new window) · Programmable LCD Settings (opens in a new window) · Standard Control Panel (opens in a new window) – QLn Series User Guide (P1028026-06EN Rev. A) (official documentation).