Start with a clean baseline
Print one controlled reference before cleaning, aligning, replacing ink/toner or reinstalling software. A repeatable defect on the same part of a DeviceOK reference is stronger evidence than a single bad document.
Live evidence
Relevant checks
Keyboard TestPress keys and verify that the browser receives the expected keyboard events.
→WebHID Device TestRequest a compatible HID device in browsers that support WebHID and display its browser-exposed product and vendor identifiers.
→4×6 Shipping Label Print TestPrint a 4×6-style reference label to inspect thermal/label sizing, clipping, barcode sharpness, and scaling.
→Browser Online Status TestCheck the browser online state, available connection hints, and a short round trip to DeviceOK.
→First sequence
Do the high-signal checks before risky changes
- 1
Test each peripheral independently
- 2
Separate network/POS app issues from input/output hardware
- 3
Use payment vendor support for secure card-reader errors
Decision points
What the result should change
If only one document prints badlyPrioritize application, PDF/font, scaling or document rendering before printer hardware.
If the same color/banding defect appears on controlled referencesMove to the printer's official maintenance/nozzle/toner/drum path.
If a local self-test is clean but computer prints are badPrioritize driver, queue, print mode, scaling or network path.
Browser can help check
- Observe keyboard-wedge scanner input
- Access compatible HID devices with permission
- Generate print references and test web connectivity
Browser cannot prove
- Diagnose payment-card reader security modules
- Bypass certified payment software
- Inspect proprietary POS firmware
Repair boundary
Know when to stop browser troubleshooting
- Do not repeatedly deep-clean inkjets without manufacturer guidance; cleaning consumes ink and can add waste-ink load.
- Laser fusers and internal high-voltage areas are not browser-serviceable.
- Use exact model consumables; similar-looking cartridge numbers are not proof of compatibility.
Used-device inspection
What to verify before paying or signing off a repair
- Print color/grayscale or fine-line references
- Check duplex/feed/ADF if the model has them
- Verify exact cartridge/toner/drum family and local availability