Scanner Types Wrong Characters
or Gibberish.
A scanner does not decide what a character looks like. It sends keystrokes, and the operating system renders them through the active keyboard layout, so a mismatch between scanner and till turns digits into symbols. These retail hardware troubleshooting guides cover the two fixes that settle almost every case.
What Wrong Characters Are Telling You
A scanner does not transmit letters and numbers but keystroke codes, and the operating system decides which character each code represents. When the scanner and the till disagree about that mapping, a healthy scanner produces output that looks broken.
This is a configuration symptom, not a hardware symptom. Every row below is resolved by changing a setting on the scanner or on the host. None of them is settled by replacing the scanner, because a fresh unit with the same defaults reproduces the identical output. Where the characters are right but nothing reaches the host at all, the fault is in a scanner that beeps but sends no data, and the rest of the set sits in the troubleshooting index.
| Symptom | Cause | Fix |
|---|---|---|
| Digits appear as !@# or other symbols | Keyboard layout mismatch between scanner and host | Set both sides to the same layout |
| y and z swapped, punctuation in the wrong place | A non-US layout is active on the host | Match the host layout, or switch the scanner |
| Extra characters arrive before or after the data | A prefix or suffix the application does not expect | Remove the prefix, set the expected suffix |
| Correct in Notepad, wrong in the POS application | The application expects a different suffix or character set | Correct the application-side terminator |
| Random symbols in the middle of a string | Baud rate or serial format mismatch on a serial model | Set 9600 baud, 8 data bits, 1 stop bit, no parity |
Two Fixes Cover Almost Everything
There are two directions in which to close a layout mismatch: change the scanner to suit the host, or change the host to suit the scanner. Try them in that order, because the first leaves the till's own settings untouched.
Make the scanner suit the system
From the scanner's configuration sheet, scan the entry that makes the unit send characters the host reads literally. On most desktop scanners this is the International keyboard entry, and some models describe the same behavior as ALT mode. Both send an unambiguous character reference instead of a raw keystroke for the active layout, which takes the host layout out of the equation entirely.
The codes differ between models, so use the sheet that came with your scanner. A code copied from another model may be ignored, or may set an unrelated parameter without any error being shown.
Make the system suit the scanner
Set the operating system keyboard layout to the one the scanner expects, which is a US English layout by default on most desktop scanners. On Windows this is under Time & Language in Settings, or through the language indicator in the taskbar.
If a till is shared between operators who type in a local language, changing the system layout is a poor trade, because the cashier's physical keyboard follows the same setting. In that case Fix 1 is cleaner: it changes the scanner and leaves the host alone. After any change, re-test in the application the operator actually uses, since a layout that reads correctly in a browser field may still fail in a POS application.
Establish the baseline first. Most desktop scanners ship with a US English layout, no prefix and a carriage return suffix only, and a baud rate of 9600 with eight data bits, one stop bit and no parity. Any of those being different from the host's expectation produces the symptoms above. Restoring defaults returns the unit to that known state; it normally requires scanning an enable-parameter-scanning code first, then the restore code, and both are printed in the model sheet.
Work Through the Layers in Order
The six layers run from the supply through to the scan engine. Wrong characters almost always sit at the configuration layer, but the earlier checks take seconds and stop you tuning settings to compensate for a cable that is only half seated.
Layer 1 — Power
A cabled scanner draws power from its host, so an under-supplied port shows up as dropped keystrokes rather than as a dead unit. A scanner that truncates a string, or that misses the first character of a scan, is sometimes drawing more current than the port will give it. Use a rear-panel port and a data extension lead.
Layer 2 — Cable
Reseat the cable at both ends with the host powered down, then try a different port. A marginal cable produces intermittent or partial characters, which is easy to mistake for a layout fault. Where the scanner has a detachable coiled lead, check that the connector is fully latched at the scanner body as well as at the host.
Layer 3 — Media, replaced by label quality
A scanner has no consumable, so the media layer becomes the label itself. Glossy or laminated labels reflect the illumination back into the sensor, and a partially reflective label can decode into the wrong characters rather than simply failing. Angling the scanner so the illumination does not bounce back, or moving it slightly closer for small barcodes, changes the read.
Layer 4 — Driver
In keyboard mode the scanner borrows the operating system's own keyboard driver, so there is nothing to install and the layout setting is the whole of this layer. In USB-to-serial mode a driver is required, and the COM port it creates is the one the application must open. A scanner replugged into a different port can leave the application pointing at a port that no longer exists.
Layer 5 — Software
This is where most wrong-character faults live. The application interprets the incoming string against its own rules: which characters it accepts, how long the field is, and what terminator ends the entry. An application expecting a carriage return that receives a carriage return plus a line feed often stores the value and treats the trailing character as a new field.
Layer 6 — Hardware
A failing scan engine, a dirty or scored window, or an internally damaged cable is the last possibility. Substituting a known-good scanner of the same interface settles it in one step: if the replacement produces the same wrong characters, the fault was never in the scanner.
The Key Discriminator
One test splits this fault in two, and it takes seconds. Run it before changing anything, because it decides which half of the repair you are in.
- 1Open a plain text editor such as Notepad and click inside the document so the cursor is blinking.
- 2Scan a barcode whose correct value is known, ideally one you can read by eye.
- 3Compare the characters in the editor with the characters printed under the barcode.
Wrong in Notepad as well
The mismatch is between the scanner and the operating system, so it appears everywhere the scanner types. This is the case for the layout fixes above: change the scanner to suit the host, or the host to suit the scanner, and the editor output corrects itself first.
Correct in Notepad, wrong in the POS
The scanner is emitting exactly the right characters. The application is interpreting them against a different expectation, almost always a suffix or a character-set assumption. This is the discriminator: the problem is the POS suffix expectation, not the scanner.
If the output is wrong everywhere, the mismatch is between the scanner and the operating system and Fix 1 or Fix 2 applies. If it is correct in the editor but wrong in the till, the scanner is already doing its job, and every change made on the scanner is a change in the wrong place. That is why these calls so often end in a needless replacement: the unit was reading and delivering correctly, while a suffix setting in the till went unexamined.
Repair or Replace
Almost every wrong-character case is configuration. The table below separates the faults you can settle at the till from the small number that genuinely need a new unit.
| What you see | Replace the scanner? | Correct action |
|---|---|---|
| Digits become symbols in every application | No — keyboard layout | Apply Fix 1 or Fix 2 |
| Correct in Notepad, wrong in the till | No — POS suffix expectation | Correct the terminator in the application |
| Wrong everywhere after both fixes; scored window | Maybe — confirm by substitution | Clean first, then fit a known-good unit |
| No beep, no illumination, no output at all | Yes — likely hardware | Confirm the port with another device, then replace |
You can do this on site
- · Scan the layout entry to enable International keyboard or ALT mode
- · Restore factory defaults, then re-apply the layout
- · Clean the window with a soft brush and a lens cloth
Contact your supplier
- · The configuration sheet is missing and a parameter has to be changed
- · A scored or damaged window that changes reads after cleaning
- · A scan engine that no longer decodes reliably
- · An internal cable fault, where a known-good scanner behaves correctly
Warranty and self-repair
No check in this guide requires opening the scanner, so nothing here affects warranty cover. Where a repair elsewhere does involve opening a device, doing so does not by itself void cover for non-human-induced defects, and a fault unrelated to the work stays eligible.
Damage caused during a repair is not covered: a window scored during cleaning, a connector broken at the board, incorrect parts, or liquid ingress. Replacement spare parts carry their own warranty period, which is one year.
Safety boundaries
- · Power the host down before reseating a cable or moving a scanner between ports.
- · Clean the window with a soft brush for dust and a lens cloth for smears. Do not spray liquid into the housing.
- · Do not use cleaning solvents on the window; water is the limit.
- · Do not open the sealed scan head. A decoder fault is a supplier matter, not a field repair.
Related Troubleshooting Guides
If the scanner reads but sends nothing, or the connection drops in and out, the guides below cover those neighbouring cases.
Scanner Beeps But No Data Appears
The read succeeds but nothing arrives — interface mode, suffix and port checks.
Printer Prints Gibberish Characters
The same family of fault on the output side — driver, baud rate and protocol.
Wireless Scanner Keeps Dropping Connection
Reads succeed and then stop — receiver placement, pairing and battery state.
Browse Barcode Scanners
Cabled and wireless models with the interface modes described above.