Zebra ZD420 troubleshooting guide: errors, faults and fixes

Short answer: A solid red STATUS light indicates, among other things, a cover or head that is not properly closed (Zebra alert “Printhead Open”). Lower the cover and press its two front corners until the latches click; if the light stays red with the cover latched, Zebra blames the head-open switch and refers you to a technician.

Likely cause

According to Zebra, the alert is triggered if the cover has been left open or not closed properly when a print is requested or FEED is pressed. The guide also mentions a head-open switch that needs repairing.

What to do

1. Lower the cover and press its two front corners until the latches engage.
2. If SUPPLIES is also solid red, the media has run out: see the Media Out entry.
3. Restart printing or press FEED: solid green STATUS means that the ZD420 is ready.
4. If STATUS stays red even though the cover is properly latched, the head-open switch is probably faulty.

When to call a technician: if STATUS stays red with the cover latched, Zebra asks you to have the head-open switch repaired by a technician.

Sources: Resolve Alerts and Errors (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Solid red STATUS and SUPPLIES correspond to the “Media Out” alert: the ZD420 can no longer see any labels. If the roll is not empty, look for a label missing from the liner or a sensor that is badly adjusted or dirty, then recalibrate with SmartCal.

Likely cause

Zebra lists six possible causes: no media loaded; a label missing at the end of the roll; sensor misaligned; printer set for labels while continuous media is loaded; dirty sensor; faulty detection due to corrupted data or a defective component.

What to do

1. End of roll: take out the rest of the media and the core, fit a new roll, close the printer and press FEED once. Leave the printer on during the operation to keep the current job.
2. Label missing in the middle of the roll: advance the media by hand past the gap until the next label is on the platen roller, close the printer, then press FEED once.
3. Black mark or notched media: align the arrow on the movable sensor with the mark or notch and recalibrate if necessary (SmartCal calibration).
4. Continuous media in a printer set for labels: move the sensor back to the centre, its default position, and recalibrate.
5. Dirty sensors: clean the upper gap sensor and the lower movable sensor, then reload, adjust and recalibrate.
6. Detection still not working: reload the firmware (firmware update).

When to call a technician: if detection is still faulty after reloading the firmware, Zebra refers you to a technician.

After changing the media (dimensions, supplier or batch), Zebra asks you to recalibrate the printer.

Sources: Resolve Alerts and Errors (opens in a new window) · Recovering from a Media-Out Condition (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The ZD420t is reporting that it has no usable ribbon left: the cartridge has reached the end of its ribbon, there is no cartridge while the printer is in thermal transfer mode, or it cannot read the cartridge. Replace the used cartridge, close the printer and press FEED once.

Likely cause

According to Zebra, the printer detects the end of the ribbon by means of the reflective section at the end of genuine Zebra ribbons. For cartridge models, the guide adds two causes: a cartridge that is required but missing (printer set to thermal transfer), and a cartridge that cannot be read because of a dirty chip or contacts, corrupted memory data or a defective part.

What to do

1. Cartridge used up: open the printer, remove the used cartridge, install a new one (see installing the cartridge), close the printer and press FEED once; you may need to press PAUSE to resume the job.
2. No cartridge in place: in thermal transfer mode, the ZD420t requires a cartridge; install one.
3. Cartridge present but not detected: the chip or the contacts may be dirty; follow the cartridge not recognised entry.

When to call a technician: if the cartridge is still not detected after cleaning the contacts, trying another cartridge and reloading the firmware, Zebra asks you to call a technician.

Sources: Resolve Alerts and Errors (opens in a new window) · Recovering from a Ribbon-Out Condition (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) · Resolve Miscellaneous Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The ZD420t is set to direct thermal while a ribbon cartridge is installed. To print in direct thermal mode, remove the cartridge without turning the printer off; to print with the ribbon, switch the print method back to thermal transfer.

Likely cause

Zebra cites two cases: a print command sent in direct thermal mode while a cartridge is in place; or a printer left in direct thermal mode while printing on thermal transfer media with a ribbon, often because the format contains ^MTD instead of ^MTT.

What to do

1. You want to print in direct thermal mode: remove the cartridge without switching the power off, close the printer, then press FEED or PAUSE once to resume.
2. You want to print with the ribbon: the label format may contain ^MTD instead of ^MTT; correct the ZPL command.
3. You can also set PRINT METHOD to thermal transfer from the print server web page, on printers connected over Ethernet (LAN or WLAN).

This alert exists only on the ZD420 with a ribbon cartridge. The guide also mentions setting it through the Settings menu, which is only available on printers with a display, which is not the case with the ZD420.

Sources: Resolve Alerts and Errors (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: This is the “Ribbon Low” alert: the cartridge is almost empty, with about 10% of the ribbon left. Printing can continue; have a new cartridge ready.

Likely cause

According to Zebra, the default alert threshold corresponds to about 10% of the ribbon remaining in the cartridge; it can be changed by command.

What to do

1. Have a new Zebra ribbon cartridge ready.
2. Replace the cartridge when the Ribbon Out alert appears.
3. To move the alert threshold, send the SGD command ribbon.ribbon_low.warning, for example ! U1 setvar "ribbon.ribbon_low.warning" "75"; Zebra lists the values off, 5, 10, 15, 25, 50, 75 and 100.
4. The Open Communication With Printer function in Zebra Setup Utilities lets you send these commands and read the printer's response.

Alert specific to the ZD420 with a ribbon cartridge.

Sources: Resolve Alerts and Errors (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) · Ribbon Cartridge Programming Commands (opens in a new window) · Standard Interface Controls (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The blade is jammed by media, adhesive or an object. Zebra only asks you to turn the ZD420 off by holding POWER for 5 seconds, wait until it has shut down completely, then turn it back on; if it does not start working again, call in a technician.

Likely cause

Zebra describes a jammed cutter blade that no longer moves normally, because of media, adhesive or a foreign object.

Caution: Do not remove the cutter cover and do not put fingers or objects into it. Zebra warns that unapproved tools, cotton swabs and solvents, including alcohol, can damage the cutter or cause jams.

What to do

1. Hold down POWER for 5 seconds to turn the printer off.
2. Wait until it has shut down completely, then switch it back on.
3. If the fault persists, do not work on the cutter: none of its parts are operator-serviceable.

When to call a technician: if the ZD420 does not recover after restarting, Zebra asks you to call a technician.

Sources: Resolve Alerts and Errors (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Solid yellow STATUS indicates, among other things, a head that is too hot (“Printhead Over Temp”): printing resumes on its own after cooling. Flashing yellow STATUS indicates a head that is too cold (“Printhead Under Temp”): turn the ZD420 off and let it warm up in a warmer room.

Likely cause

For overheating, Zebra cites a large batch of labels or an ambient temperature above the operating range (direct sunlight, for example); for a head that is too cold, an environment below the minimum operating temperature.

Caution: According to Zebra, the printhead can cause severe burns: wait until it has cooled down before handling it. Also avoid sudden changes in temperature, which can cause condensation.

What to do

1. Solid yellow STATUS during a long run: let the head cool down, printing resumes automatically.
2. If the room is too hot or the printer is in the sun, move it or cool the room.
3. Flashing yellow STATUS: turn the printer off, place it somewhere warmer and let it come up to temperature naturally.
4. If STATUS is solid yellow and DATA is flashing yellow, the memory is insufficient: see Out of Memory.

Sources: Resolve Alerts and Errors (opens in a new window) · Status – Printhead Operation (opens in a new window) · Standard Interface Controls (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: This double red flashing indicates head overheating that requires cooling down and restarting. Turn the ZD420 off (POWER held for 5 seconds), wait several minutes, then turn it back on; if the fault returns, contact a technician.

Likely cause

The guide associates this case with an overheating head (Printhead Shutdown). It treats a head that has reached a critical temperature or suffered a power failure, and a faulty head thermistor, in the same way.

Caution: According to Zebra, the printhead can cause severe burns: wait until it has cooled down before handling it.

What to do

1. Turn the printer off by holding down POWER for 5 seconds, then wait until it has shut down completely.
2. Wait several minutes for the head to cool down completely.
3. Switch the printer back on.
4. If the fault reappears, do not remove the head: Zebra declares it not operator-serviceable.

When to call a technician: if the error returns after restarting (overheating, critical failure or thermistor), Zebra asks for a technician to intervene.

Sources: Resolve Alerts and Errors (opens in a new window) · Status – Printhead Operation (opens in a new window) · Standard Interface Controls (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: With STATUS solid yellow, this is the “Out of Memory” alert: there is not enough memory to save a format, graphic or font. Simplify the label and clear out the stored items.

Likely cause

The Zebra guide explains that the available memory (graphics, formats, bitmaps, fonts) is too low to carry out the requested function.

What to do

1. Reduce the size of the format or the printed area.
2. Delete stored graphics, fonts and formats that you no longer need.
3. Make sure that the data is not directed to a storage device that is missing or unavailable.

Sources: Resolve Alerts and Errors (opens in a new window) · Standard Interface Controls (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The ZD420 calibrates without software: when STATUS is solid green, press PAUSE and CANCEL at the same time for 2 seconds, then release. The printer feeds and measures a few labels, then STATUS returns to solid green.

Likely cause

During SmartCal calibration, the printer identifies the media type (gap labels, black marks or notches, continuous) and sets its detection. Zebra specifies that a new batch of the same type of media does not require recalibration.

Official SmartCal calibration procedure

1. Load the media (and the ribbon cartridge on a ZD420t) and close the cover.
2. Switch the printer on and wait until STATUS is solid green.
3. Press PAUSE and CANCEL simultaneously for 2 seconds, then release.
4. The ZD420 measures several labels and adjusts its detection thresholds; STATUS returns to solid green when it has finished.

For a new roll from the same batch, pressing FEED once or twice is enough according to Zebra. If the media is not recognised, move on to manual calibration.

Sources: Running a SmartCal Media Calibration (opens in a new window) · Resolve Print Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Enter advanced mode by holding PAUSE for 2 seconds: solid yellow STATUS corresponds to manual calibration. The printer then measures, in two stages, the liner on its own and then a label, as you press PAUSE.

Likely cause

Zebra offers this calibration for media that automatic calibration does not identify correctly.

Official manual calibration procedure

1. With media loaded and the printer on, hold PAUSE for 2 seconds: all the lights flash yellow, then STATUS stays solid yellow.
2. Press PAUSE to start the manual calibration: SUPPLIES flashes yellow, then it is PAUSE's turn.
3. Open the cover and position the movable sensor: in the centre, on the alignment arrow, for gap labels; opposite the mark or notch for marked media; where it sees the least printing for pre-printed media.
4. Remove the labels from about 80 mm of liner.
5. Place this bare section over the platen roller, with the start of the first label under the guides.
6. Close the cover and press PAUSE once: the media light flashes during the measurement, then PAUSE flashes.
7. Open the printer again and advance the media so that a label is just above the movable sensor.
8. Close the printer and press PAUSE once: the ZD420 measures several labels and returns to the ready state if it has identified the media type and length.

Zebra points out that you sometimes need to repeat this several times, moving the sensor. CANCEL exits advanced mode.

Sources: Activating Advanced Mode (opens in a new window) · Manually Calibrating Media (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The media is incorrectly loaded, the movable sensor is badly positioned or the printer is not calibrated for this media. Check the sensor position and run a SmartCal calibration again; the same calibration fixes the case of labels treated as continuous paper.

Likely cause

Zebra calls this a registration fault and cites: media incorrectly loaded or movable sensor badly adjusted; sensors not calibrated for the length, material or detection type; platen roller slipping or damaged; cable or communication settings problem. The guide adds that labels treated as continuous media are due to uncalibrated media or a continuous media configuration.

What to do

1. Check the loading and the position of the movable sensor (see loading labels).
2. Run a SmartCal calibration again; if the printer is treating your labels as continuous media, this calibration makes it relearn the media type.
3. If labels are still skipped or the media is difficult to detect, run a manual calibration.
4. If the platen roller is slipping or damaged, clean or replace it (see faded print).
5. If the first labels are correct and the fault appears afterwards, check the link with the computer (see communication problems).

Sources: Resolve Print Issues (opens in a new window) · Resolve Miscellaneous Issues (opens in a new window) · Loading Media (opens in a new window) · Running a SmartCal Media Calibration (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Open the printer, hold the cartridge by its grip area and slide it into its slot along the guide rails until it clicks. Close the printer: the ZD420t reads the cartridge chip and prints in thermal transfer mode.

Likely cause

The ZD420t uses the cartridge for thermal transfer printing. A chip reader in the ribbon mechanism reads the information stored in the cartridge.

Official cartridge installation procedure

1. Open the printer.
2. Grip the cartridge by the marked grip area (A) and insert the end marked B first.
3. Slide the cartridge into its slot on the ribbon mechanism, following the guide rails.
4. Push until it is almost flush with the front of the mechanism: it locks with a click that you can hear and feel.
5. Close the printer.

Zebra specifies that only genuine Zebra ribbon cartridges are supported, neither refurbished nor other brands. If the printer cannot authenticate the cartridge, see cartridge not recognised.

Sources: Loading the ZD420 Ribbon Cartridge (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: If the cartridge is a genuine Zebra cartridge, unmodified and not refurbished, the contacts on its chip or the pins of the cartridge sensor are probably dirty, or the chip is damaged. Clean the chip contacts with alcohol, try another cartridge, then clean the sensor pins.

Likely cause

According to Zebra, the printer can wrongly show a ribbon out alert while a cartridge is in place, or an authentication failure with a genuine Zebra cartridge, when the cartridge sensor pins or the chip contacts are dirty, or the chip is damaged. The Zebra status page also points out that only genuine Zebra cartridges are supported (neither refurbished nor other brands) and that “Cartridge Authentication Failed” indicates a cartridge that cannot be authenticated or has been modified.

What to do

1. If the contacts on the cartridge chip look dirty, clean them with a cotton swab very lightly moistened with alcohol.
2. If the error persists, try another cartridge.
3. Clean the contact pins of the cartridge sensor, in the upper part of the printer, following the procedure in the Zebra guide for cartridge ZD420 models.
4. Reload the firmware (see firmware update).

When to call a technician: if the printer does not recover, Zebra asks you to call a technician: the cartridge sensor is not user-serviceable.

Sources: Resolve Miscellaneous Issues (opens in a new window) · Status – Typical Operating Conditions (opens in a new window) · Resolve Alerts and Errors (opens in a new window) · Loading the ZD420 Ribbon Cartridge (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The roll sits on the two roll holders with the printable side facing up; it must turn freely and not touch the bottom of the compartment. Pass the media under both guides, then place the movable sensor in the centre, or on the black mark for marked media.

Likely cause

Zebra links incorrect loading or a badly adjusted sensor to several faults: media out reported wrongly, skipped labels, labels with no printing.

Official loading procedure

1. Pull the release levers towards you to open the printer.
2. Open the roll holders and orient the roll so that the side to be printed is on top as it passes over the platen roller.
3. Pull the guides apart, fit the roll, then release them; the roll must turn without friction and without resting on the bottom of the compartment.
4. Bring the media out through the front of the printer and slide it under both guides.
5. Position the movable sensor: in the centre for labels separated by gaps or continuous media; for media with black marks, notches or holes, sensor arrow in the centre of the mark, as far as possible from the edge as long as the mark covers the whole sensor window.
6. For a new type of media, close the printer and run a SmartCal calibration.

Allow a margin for the sensor: according to Zebra, the media can shift sideways by about 1 mm during printing. The off-centre sensor position is only for black mark media. Models with a cutter follow a specific loading procedure described in the guide.

Sources: Loading Media (opens in a new window) · Adjusting the Movable Sensor for Black Marks or Notches (opens in a new window) · Setting Media Sensing by Media type (opens in a new window) · Recovering from a Media-Out Condition (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Zebra first cites a darkness or speed setting unsuited to the media, then a dirty printhead, a dirty platen roller or a worn head. Print the print quality report to choose the right setting, then clean the head with a new cleaning pen.

Likely cause

The Zebra guide lists four causes of poor print quality: a wrong darkness / speed combination, a dirty head, a dirty or damaged platen roller, a head that has reached the end of its life or is damaged.

Caution: The head is hot after printing: do not touch it. Take the anti-static precautions required by Zebra before working on the head or under the cover. Never re-moisten a swab that has already been used.

What to do

1. Print the print quality report (FEED self-test): the ZD420 prints labels from -3 to +3 around the current darkness, at a slow speed and a fast speed; keep the setting that produces compliant barcodes.
2. Do not exceed the maximum speed specified by the media manufacturer.
3. Clean the printhead with a new cleaning pen (see the frequency in the note).
4. Dirty platen roller: release it by pulling its two bearing tabs towards you and then upwards, remove the gear and the bearings, clean it from the centre outwards with a swab very lightly moistened with 99% isopropyl alcohol, refit it with the gear on the left and let it dry for one minute.
5. Worn or damaged head: the Zebra guide provides for its replacement.

Zebra recommends cleaning the head each time the media roll is changed for optimum quality; its recommended maintenance schedule provides for cleaning after every five rolls printed. Never use a pen that has already been used: it carries contaminants. For a linerless media platen roller, use no product: simply press the adhesive side of a piece of that media onto the roller.

Sources: Resolve Print Issues (opens in a new window) · Cleaning the Printhead (opens in a new window) · Recommended Cleaning Schedule (opens in a new window) · Cleaning Supplies (opens in a new window) · Printing a Print Quality Report (FEED Self-Test) (opens in a new window) · Cleaning and Replacing the Platen (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Use the manual darkness setting in advanced mode: the ZD420 prints increasingly dark patterns and you stop the series with FEED on the first pattern with solid, even black lines.

Likely cause

Zebra points out that quality depends on the combination of head heat (darkness), speed and media, and that each media may require a different darkness.

Official manual darkness adjustment procedure

1. With media loaded, hold PAUSE for 2 seconds: the ZD420 enters advanced mode.
2. Press FEED as many times as necessary for DATA to light up yellow: this is the manual darkness setting.
3. Press PAUSE: a test pattern prints with the darkness value and barcodes, then the printer starts again at the next level after a short pause.
4. When a pattern shows solid, even black lines, press FEED: this level is saved and the printer returns to the ready state.

Without a display, the ZD420 can also be set from the computer: speed in the Windows driver or ZebraDesigner, darkness and speed with the Configure Print Quality function in Zebra Setup Utilities. CANCEL exits advanced mode.

Sources: Activating Advanced Mode (opens in a new window) · Manual Print Darkness Adjustment (opens in a new window) · Adjusting the Print Quality (opens in a new window) · Printing a Print Quality Report (FEED Self-Test) (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The cartridge ribbon (wax, wax-resin or resin) may not suit the media, or the speed exceeds what the cartridge can handle. Set the speed no higher than the maximum speed recommended for the cartridge and use the power supply supplied with the printer.

Likely cause

In thermal transfer, Zebra cites a ribbon material unsuited to the media and the wrong power supply.

What to do

1. Do not exceed the maximum speed recommended for the installed cartridge.
2. To find out which cartridge is installed, query the printer with Zebra's SGD commands, for example ribbon.cartridge.type or ribbon.cartridge.part_number (! U1 getvar command).
3. Check that the ribbon / media combination is consistent: wax, wax-resin or resin depending on whether the media is paper, coated paper or synthetic.
4. Check that the power supply is the one delivered with the printer.

Sources: Resolve Print Issues (opens in a new window) · Ribbon Cartridge Programming Commands (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The media does not match the print mode or it is loaded upside down. A ZD420d requires direct thermal media; and in all cases, the printable side must face up, towards the head.

Likely cause

Zebra explains the absence of printing by unsuitable media (not intended for thermal transfer or for direct thermal) or media loaded the wrong way round.

What to do

1. Identify your model: the ZD420d prints only on direct thermal media, the ZD420t on thermal transfer media with its ribbon cartridge.
2. If the roll is upside down, refit it so that the side to be printed faces up, under the head (see loading labels).

Sources: Resolve Print Issues (opens in a new window) · Loading Media (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: The printer only accepts genuine Zebra heads and must be able to read their resolution. If the head is not genuine, replace it with a Zebra head; if it is, redo its installation following the procedure in the guide.

Likely cause

Zebra distinguishes two states: “Unauthorized Printhead Error”, a head that is not a genuine Zebra head; “Printhead Resolution Error”, head resolution (dpi) unreadable, probably because it is incorrectly installed or is not a Zebra head. The solid red STATUS light covers head authentication failure.

Caution: Zebra asks you to unplug the printer, let it cool down and work at an anti-static workstation (grounded conductive mat and anti-static wrist strap) before touching the head.

What to do

1. Check that the fitted head is a genuine Zebra head.
2. If the head has just been changed, redo its installation following the head replacement procedure in the Zebra guide.
3. Once a genuine Zebra head is correctly installed, printing can resume.

Sources: Status – Printhead Operation (opens in a new window) · Standard Interface Controls (opens in a new window) · Replacing the Printhead (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Windows has probably installed its generic driver because the ZD420 was connected before the Zebra driver. Disconnect the USB cable, remove the Zebra entries classified under “Unspecified”, install the latest Zebra driver, then reconnect.

Likely cause

According to Zebra, a printer connected by USB before its driver is installed is handled by the generic Windows driver, and the Windows test page fails.

What to do

1. Remove the USB cable from the computer.
2. In Windows, open Control Panel > Devices and Printers and find the Zebra printers with the ZTC prefix under “Unspecified”.
3. Remove these entries.
4. Install the latest version of the Zebra Windows driver.
5. Reconnect the USB cable: the ZD420 then appears in the Printers section.

Source: Resolve Communication Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: If DATA does not flash when data is sent, the data is not arriving: check the communication settings and the serial cable. If a few labels come out and then deteriorate, compare the serial settings and the prefix and delimiter characters, and run the communication diagnostics test.

Likely cause

The Zebra guide cites incorrect communication settings, a serial cable that is non-standard, damaged or too long, serial settings (flow control) that differ from the computer's, prefix and delimiter characters that do not match the format, and incorrect data.

What to do

1. Nothing comes out and DATA stays still: check the communication settings in the driver or the software; on serial, match the handshake protocol and port settings with those of the computer.
2. Serial cable: use a standard DTE or DCE cable, in good condition, of a length that complies with the RS-232 standard.
3. Labels correct and then skipped, shifted or distorted: check the flow control and the other serial settings, then the prefix (COMMAND CHAR) and delimiter (DELIM./CHAR) characters against the ZPL format.
4. Diagnostic test: with media loaded and the print width no greater than the label width, hold PAUSE and FEED for 2 seconds; STATUS alternates between green and yellow and the ZD420 prints everything it receives, in ASCII and in hexadecimal.
5. Read the diagnostic label: FE (framing error), OE (overrun), PE (parity) or NE (noise) indicate communication settings that need correcting. To exit, hold PAUSE and FEED again for 2 seconds, or restart the printer.

Sources: Resolve Communication Issues (opens in a new window) · Performing a Communication Diagnostics Test (opens in a new window) · Standard Interface Controls (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Solid red: Ethernet or Wi-Fi connection fault, the printer is not on the network. Flashing red then yellow: Wi-Fi connection in progress; green: connected (flashing if the Wi-Fi signal is weak); off: no Ethernet link. If the network settings are the cause, Zebra provides for resetting them to their factory values.

Likely cause

Zebra describes each state of the NETWORK light in the guide: solid red corresponds to an Ethernet (LAN) or Wi-Fi (WLAN) link error.

What to do

1. Solid green: 10/100 Ethernet detected or Wi-Fi connected with a good signal. Solid yellow: 10Base Ethernet detected.
2. Flashing red then flashing yellow: Wi-Fi association then authentication; wait for the connection to complete.
3. Flashing green: Wi-Fi connected but weak signal.
4. Solid red: Ethernet or Wi-Fi link error. To restore the factory network settings, with the printer off, hold PAUSE and CANCEL, turn it back on and keep them held down until only STATUS is on.
5. Alternatively, press the RESET button underneath the printer for 6 to 10 seconds with a paper clip: the ZD420 restores its factory network settings and prints its printer and network configuration reports.

This guide does not reproduce any access credentials for the print server: refer to the Zebra documentation.

Sources: Standard Interface Controls (opens in a new window) · Status – Wi-Fi (WLAN) Option (opens in a new window) · Status – Ethernet (LAN) Option (opens in a new window) · Resetting the Printer's Network Settings to Their Factory Defaults (opens in a new window) · RESET Button Functions (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Maintenance is limited to the plastic surfaces the media passes over, at the cutter inlet and outlet: a swab or lint-free cloth very lightly moistened with 99% isopropyl alcohol. The blades and the mechanism are not cleaned.

Likely cause

According to Zebra, the blade has a coating that resists adhesive and wear: it does not need cleaning and cleaning it may damage it.

Caution: No part of the cutter is operator-serviceable. Do not remove its cover, do not touch the blades or the mechanism and do not insert fingers or objects into it. Zebra warns against unapproved tools, cotton swabs and solvents, including alcohol, which can damage the cutter or cause jams.

Official cutter cleaning procedure

1. Lightly moisten a clean swab or a lint-free cloth with 99% isopropyl alcohol.
2. Wipe the ridges and plastic parts of the media inlet, inside the cutter, then of the exit slot, on the outside.
3. Repeat until the adhesive and deposits have been removed.
4. Let it dry before resuming printing.

When to call a technician: beyond cleaning the surrounding area, any cutter maintenance is a job for a technician according to the Zebra maintenance schedule.

Sources: Cleaning the Cutter Option (opens in a new window) · Recommended Cleaning Schedule (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Look at the light on the power supply: if it is not green, the mains socket is not supplying power. If the power supply is live, hold POWER until the lights flash; after the self-test, only STATUS stays lit in green.

Likely cause

Zebra documents three useful points here: the electrical connection, the power-on sequence with its self-test, and the battery base, whose complete discharge prevents the printer from starting.

Caution: Zebra prohibits using the printer or its power supply in a damp place, because of the risk of serious injury. Use a cord with a three-pin plug and an IEC 60320-C13 connector and keep the socket accessible so that the power can be cut off.

What to do

1. Check the power chain: power supply plugged into the printer's DC socket, mains cord connected to the power supply and to a wall socket.
2. The light on the power supply should be green: if not, the mains socket has no power.
3. Press POWER until the lights flash; the self-test lasts a few seconds and ends with only STATUS on, solid green.
4. If the ZD420 is mounted on the optional battery base: wake the battery with its button (all its lights flash three times) and turn the printer on within one minute. With no charge bar lit, the battery needs recharging and the printer will not start.

Sources: Attaching the Printer to Power (opens in a new window) · Standard Interface Controls (opens in a new window) · Power-On Self Test (opens in a new window) · Battery Indicators and Controls (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Solid red: internal battery error, battery at end of life or faulty; Zebra asks you to replace it. Flashing red: charging error, in particular a battery that is too hot or too cold; let it return to room temperature before recharging it.

Likely cause

Zebra links solid red to a battery at the end of its life or a component failure, and flashing red to a charging error: temperature out of range or internal monitoring error.

What to do

1. Solid red: take the battery out of the printer and replace it.
2. Flashing red: remove the battery and check its condition by putting it on charge.
3. Let it return to room temperature, then check its charge again.
4. If the temperature and the charge are not the cause, replace the battery.

Green: battery in good condition and charged; yellow: charging, printer off. Zebra states about two hours to recharge an empty battery, and no charging while printing or feeding media.

Sources: Resolve Miscellaneous Issues (opens in a new window) · Battery Indicators and Controls (opens in a new window) · Printing with the Attached Battery Base and Battery Option (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Get the firmware from the Zebra support page for your ZD420, then transfer it with Zebra Setup Utilities: Open Printer Tools, Action tab, Send file. The printer restarts and prints a configuration report when the update is complete.

Likely cause

Zebra recommends regular firmware updates and also asks you to reload it if media or cartridge detection fails, if settings are lost or if the printer locks up.

Official update procedure

1. Download the firmware from the Zebra support page for the model: zebra.com/zd420c-info for the cartridge version, zebra.com/zd420d-info for the direct thermal version.
2. Start Zebra Setup Utilities, select the ZD420 and click Open Printer Tools.
3. In the Action tab, check that media is loaded in the printer, then click Send file.
4. Using the browse button (...), select the downloaded firmware file.
5. Follow the lights: DATA flashes green during the transfer, all the lights flash on restart, STATUS is solid green during validation and installation; printing of a configuration report marks the end.

If the version sent is identical to the one installed, the firmware is not transferred.

Sources: Updating Printer Firmware (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide · ZD620 and ZD420, Link-OS 4-inch desktop printers, user guide (P1131665-01FR) (opens in a new window) – Zebra ZD620 and ZD420 user guide (French PDF) · Resolve Alerts and Errors (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide · Resolve Miscellaneous Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Using a paper clip, press the RESET button underneath the ZD420 for 1 to 5 seconds: it performs a factory reset and prints a configuration report. From a computer, Zebra Setup Utilities offers Load printer defaults (Open Printer Tools, Action tab).

Likely cause

Zebra offers this return to factory values for settings that are not retained and for a printer that freezes.

Official reset methods

1. RESET button, 1 to 5 seconds: printer factory reset, then printing of the configuration report (and the network report if it is networked).
2. RESET button, 6 to 10 seconds, on a networked printer: only the network settings return to their factory values; the printer and network reports print.
3. Press for more than 10 seconds: exit from reset mode, no settings changed. A press of one second or less has no effect.
4. Without touching the printer: Zebra Setup Utilities > Open Printer Tools > Action tab > Load printer defaults.
5. Network settings only, using the buttons: with the printer off, hold PAUSE and CANCEL while turning it back on, until STATUS is the only light on.

Sources: RESET Button Functions (opens in a new window) · Resolve Miscellaneous Issues (opens in a new window) · Resetting the Printer's Network Settings to Their Factory Defaults (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: Most often, the changes were not saved (no ^JU command before turning off) or a command in the format resets the parameter. Restart to check, check the commands sent, then reload the default values and the firmware if necessary.

Likely cause

Zebra lists several causes: parameters set incorrectly; changes not saved because no ^JU command was sent before turning off; a syntax error or a command in the format that disables or resets a parameter; prefix and delimiter different from those of the format; faulty main logic board (MLB), due to corrupted firmware or a failure.

What to do

1. Turn the ZD420 off and on again to see whether the settings have been saved.
2. Check the use and syntax of the commands with the ZPL programming guide.
3. Print a configuration report and compare the printer's control, command and delimiter characters with those of the label format.
4. Reload the default values (Zebra Setup Utilities > Open Printer Tools > Action > Load printer defaults).
5. Reload the firmware (see firmware update).

When to call a technician: if the settings are still not retained, Zebra refers you to a technician: the main logic board is not user-serviceable.

Source: Resolve Miscellaneous Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).

Short answer: According to Zebra, a ZD420 that freezes with all its lights on, even on restart, probably has corrupted memory. Reload the default values and then the firmware; if nothing changes, call in a technician.

Likely cause

The Zebra guide mentions corruption of the printer memory.

What to do

1. In Zebra Setup Utilities, choose Open Printer Tools, then the Action tab and Load printer defaults to return to the default values.
2. If the ZD420 is still frozen, reinstall the firmware (see firmware update).

When to call a technician: if the ZD420 does not start working again, Zebra asks you to call a technician: the memory is not user-serviceable.

Source: Resolve Miscellaneous Issues (opens in a new window) – ZD620 and ZD420 Desktop Printers User Guide (official documentation).