Receipt printer printing blank, garbled, or not at all: POS troubleshooting

Store operations · 8 min read

"The printer is broken" is three different problems wearing one coat. A printer that feeds out blank paper is usually healthy hardware being fed the wrong paper. A printer producing streams of random symbols is usually healthy hardware receiving data in a form it does not expect. And a printer doing nothing at all is usually a routing problem — in an LS Central store, the job may never have left the hardware profile, the Hardware Station, or the terminal itself. The fixes do not overlap much, so the first job is naming which of the three you actually have.

Name the symptom first: blank, garbled, or silent

One more observation worth making before touching anything: is it one terminal or every terminal? A fault on a single lane points at that lane's printer, paper, and profile assignment. The same fault appearing everywhere at once points at something shared — and hardware almost never fails in unison.

The 60-second paper checks (blank and faint)

Thermal printers — the type at most registers — have no ink. They print by heating a coating on the paper itself, and that single fact explains most blank receipts:

1. Do the fingernail test. Scratch the paper firmly with a fingernail. Thermal paper leaves a black mark; ordinary paper does not. If there is no mark, the roll is bond paper, and no setting in any system will make a thermal printer print on it.
2. Check the roll direction. Thermal paper prints on one side only. On most printers the paper should feed from underneath the roll. A roll loaded the other way feeds perfectly and prints blank, because the print head is heating the uncoated side.
3. Close the lid until it clicks. Many printers only press the paper against the print head when the lid is fully closed. A lid resting shut but not latched produces blank or very faint output.
4. Try a fresh roll from a different box. Thermal paper reacts to heat: rolls stored somewhere hot — a warm van, near an oven, in direct sun — can pre-darken or print weakly. Store rolls somewhere cool and dry. If a fresh roll prints perfectly, the old roll was the problem and you are done.
5. Know your printer type. Impact printers — the Epson TM-U220 and Star SP700 are the examples most often named — print through an ink ribbon onto plain paper. On an impact printer, print that fades and then disappears usually means the ribbon is worn or missing, and loading thermal paper expectations onto it sends you in the wrong direction.
6. Check density last, not first. Some printers and POS systems expose a print density or darkness setting; turned down, receipts look washed out. Low density makes print faint — it does not make a correctly loaded thermal roll come out completely blank, so rule out paper and direction before reaching for settings.

The self-test: cut the problem in half

Receipt printers can print entirely on their own, without the POS, the network, or any driver. The Epson TM-U220 reference describes the procedure and why it matters: make sure the printer is off and the roll paper cover is closed, hold down the FEED button while turning the printer on, and the self-test prints the printer's settings; press FEED again and it prints a pattern using its built-in character set, ending with a completion line before cutting the paper. Details vary by model, so check your own printer's manual for its exact button sequence — the principle is the same across brands.

The self-test checks the printer's control circuits, mechanisms, print quality, control software version, and switch settings, and it is independent of any other equipment or software. That independence is what makes it the most valuable test on this page:

• Clean self-test, bad POS receipts: the printer, its head, and its paper are proven good. The problem is in the other equipment or the software — driver, model selection, serial settings, or the LS Central print path. Stop cleaning the print head.
• Blank or faint self-test too: the fault lives inside the printer/paper combination. Go back to the paper checks, clean the head, and suspect a worn head if a known-good roll still prints faintly.
• No self-test at all: power or printer hardware. Check the adapter before anything else — on common Epson models the power cord can disconnect from the brick in the middle of the cord while both ends still look plugged in.

Garbled output: the printer is hearing the wrong language

Garbled receipts mean data arrived and was misinterpreted. The suspects, in order:

1. Wrong model selected. When a POS holds the wrong printer model for the physical printer, output comes out as random symbols. Correct the model to match the printer actually on the counter, save the change, power cycle the printer — off for around 30 seconds, then on — and reprint.
2. Wrong or mismatched driver. Where the terminal prints through a Windows printer, the driver must be the one for that printer. In LS Central's WinPrinter setup, the printer record points at a Windows printer by name in the Printer Device Name field, and a partial name is matched to the best fit — convenient, and an easy way to end up printing through a near-namesake printer or driver after hardware changes.
3. Serial settings mismatch. On serial-connected printers, when the computer's baud setting does not match the printer's, you get output that does not resemble what was sent: random characters, an unusual mixture of special characters, and inconsistent spacing. A parity mismatch looks subtler — some characters missing or replaced while word spacing stays roughly right. Match the settings at both ends; guessing values one at a time produces every variation of garbled.
4. A printer swap nobody finished. A replacement printer of a different model inheriting the old printer's model selection, driver, or profile assignment is the classic garbled-after-maintenance story. If the timing matches a swap, re-verify the whole assignment instead of troubleshooting the new printer as if it were the old one.

Print head cleaning sits in this section too, for faint and streaky output: with the printer off and the power cable unplugged, open the cover and wipe the thermal print head and platen roller with a cotton swab lightly moistened with isopropyl alcohol or ethanol, then let everything dry completely before testing again. Use the printer's original power adapter while you test — an incorrect adapter is a documented cause of faint and blank output, and substituting adapters mid-diagnosis muddies every result.

Nothing prints at all: work the LS Central side

If the self-test is clean and a Windows test print works — or the printer works from another terminal — but LS Central receipts never arrive, walk the print path:

1. Confirm which printer the profile names. To serve as the main POS printer, a printer is linked on the terminal's Hardware Profile: the profile's Printer field selects the POS Printer type, and in the POS Printers FastTab a line with the Job and Sub-Job fields left empty links that printer for all print jobs. A line scoped to specific jobs, or a printer linked on a different profile than the terminal actually runs, quietly reroutes or drops receipts.
2. Check the Hardware Station. Hardware Station is the device service LS Central dialogs with for OPOS and other retail devices, and Printer is one of its supported device types. If the service is stopped, pointed at the wrong host, or holding a device list from before a printer swap, a healthy printer stays silent. Re-detect the hardware rather than trusting a hand-edited device list.
3. Check power and error states at the printer. The most common causes of a printer not printing are power issues: power cycle it, secure and re-seat the cables, and confirm paper is installed and feeds. Read the LEDs before resetting anything — a paper error state and a flashing error state (which can indicate a jam) call for different fixes, and note that printing also stops when a thermal head overheats, resuming on its own once it cools.
4. For network printers, confirm the printer is still reachable. Check the network cable is seated at both ends and the printer's network status light is on, then confirm the terminal can still reach the printer at the address its configuration expects. If network equipment or the printer was replaced since the lane last worked, treat the address as suspect until you have verified it against the printer itself.
5. Remember the drawer. On a printer-driven cash drawer setup, a dead printer path is also a dead drawer. If the drawer stopped at the same moment as the receipts, you have one fault, not two — fix printing first, then work our cash drawer guide if the drawer still misbehaves.

What success looks like

Finish with the printer's own evidence, not the POS's optimism: one clean self-test kept in hand, then two consecutive receipts from the POS that are complete, legible edge to edge, and correctly formatted. On a lane with a printer-driven drawer, the drawer should also kick on the cash sale you use as the second test. If the self-test is clean but POS receipts are still garbled or missing, the printer is exonerated: keep the self-test printout, note which terminal and profile you tested, and escalate the profile, driver, and Hardware Station configuration as a software fault rather than ordering a replacement printer.

FAQ

Receipts went faint over a few weeks. Paper or printer?
Gradual fading with the same paper stock points at the print head: clean it as described above, then test with a fresh roll. If a known-good roll still prints faintly after cleaning, the head is likely worn — that is a repair or replacement decision, not a settings one.

Only special characters and totals look wrong; the item lines are fine.
Partially correct output still counts as garbled. Model, driver, and character-encoding mismatches typically corrupt some characters while others survive, and a parity mismatch on a serial printer replaces individual characters while spacing stays plausible. Work the garbled section in order.

The printer works from Windows but not from the POS. What now?
The printer, cable, and driver basics are proven. In LS Central, check the POS Printers assignment on the hardware profile the terminal actually runs, and the Hardware Station device list — the job is being routed somewhere, or nowhere, above the printer.