Zebra ZD421 skipping labels: how to find the cause
You send a batch of labels and the ZD421 leaves a blank one between prints, feeds too far or starts each print in a different position. Before changing settings, check whether it also skips without a job from the computer. That test helps you decide where to start.
1. Separate manual feeding from the print job
Let pending jobs finish and keep the application from sending more during the test. With STATUS solid green and no printing in progress, briefly press FEED: holding it down advances multiple labels. Watch where each label edge stops.
| What happens | What to check first |
|---|---|
| FEED also skips labels | Roll loading, sensor, media type and calibration. |
| FEED works; the application leaves blank labels | Page size, empty pages and settings sent with the job. |
| It only feeds at power-on, cover closure or calibration | Configured power-up or head-close action; distinguish this from skipping during a batch. |
This comparison guides troubleshooting; it does not prove the hardware is fault-free. It applies to die-cut labels with gaps or marks. Continuous paper has no gap for the sensor to find.
2. Check the roll and sensor position
Open the cover and check that the media runs under the guides, straight and without being pinched. For ordinary gap labels, use the default sensor-arrow position within the alignment area specified by Zebra. For black-mark media, align the sensor with the mark on the back as shown in the manual.
Also check the configured media type: gap, black mark or continuous. If you see dust or adhesive, follow the sensor-cleaning procedure for your printer variant. Avoid moving the sensor at random or changing margins to compensate for skipping.
3. Run SmartCal with the media correctly loaded
If feeding remains irregular, calibrate after checking loading and sensor position. SmartCal measures the media; feeding several labels during this process is normal.
- Load labels and, for thermal transfer, the appropriate ribbon. Close the cover and wait for solid green STATUS.
- Hold PAUSE and CANCEL together for two seconds, then release.
- Wait for measurement to finish and STATUS to return to solid green. Repeat the brief FEED test.
If SmartCal cannot recognize the roll, follow the model’s manual calibration procedure. A replacement roll of the same type, vendor, batch and size normally only needs one or two FEED presses to synchronize; recalibration is not required every time.
4. If FEED works, check the application and driver
Print a single label from the application that fails. Check physical page size, orientation, empty pages and copy count. For example, a 100 × 150 mm label placed on an A4 document is not the same as a 100 × 150 mm page.
Record settings before the job and compare them afterwards: the transmitted format can change configuration. For ZPL jobs, check design dimensions and DPI. The viewer helps inspect the layout, but cannot calibrate sensors or confirm physical feeding. Change one setting at a time and keep the original file.
5. Check several labels before repeating the batch
Test one label, then a short batch, such as five. Check quantity, alignment and content. If each FEED press works but one particular file brings the problem back, keep that file and review its settings with the application provider.
If FEED still fails after correct loading and manual calibration, the manual also identifies feed problems such as a slipping or damaged platen roller. Record the ZD421 variant, roll type and test results for technical support. Avoid starting with a factory reset that erases useful settings.
Frequently asked questions
Why is there exactly one blank label between prints?
The pattern alone does not identify the cause. If FEED works correctly, look for an empty page or incorrect format size in the job. If FEED also fails, start with media and sensing.
Does SmartCal waste labels?
It advances a few labels while measuring. That movement is part of calibration and does not mean a skip still occurs between each print.
Should I increase print darkness?
Darkness affects marking; it does not fix label-start detection. If every label is blank, that is a different symptom: also check thermal media, ribbon and print method.
Why does the problem return after calibration?
Check whether it returns with a particular job, a media change or a restart. That distinction helps you look for settings sent by the application, a different roll or unsaved configuration.
Related guides
Official references
About the author
Eduard Diaz
Eduard Diaz is an IT technician (development) at S-IE, an official Zebra partner with more than 20 years providing identification and labelling services. He builds and maintains EditorZPL to make working with ZPL and Zebra label printers easier.
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