Home/Scanners/Why a barcode will not scan
What has actually gone wrongA barcode that will not read is one of four things, and only two of them are the scanner. Before you buy another one, it is worth thirty seconds establishing which — because one of the four is free to fix and one of them is in a completely different machine.
This is what thirty-five years of answering that phone call sounds like, in the order the answers usually come.
The commonest cause of a barcode that will not scan is not in the scanner at all. It is in the printer that made the label, and it is usually three metres away.
A thermal printhead is a row of tiny heating elements, one per dot across the label. When one burns out it stops making a mark, and every label after that carries a white line running down it in the direction of printing.
If that line crosses the barcode it cuts every bar it passes through. The scanner is being handed a barcode with a gap in it and there is nothing to decode. It will not read, and no amount of trying a different scanner will change that.
Hold one up. A hairline white stripe running the length of the label, in the same place on every one, is a dead element and the head is finished. It will not come back and it does not need cleaning.
It also explains the thing that makes people doubt themselves: the same barcode scans perfectly off the screen and not off the label. The data was fine. The printing was not.
What a replacement printhead costs, and the other symptoms →
Corded scanners fail from age and physical abuse, and they fail in two places. Telling them apart takes about ten seconds and decides whether it is worth any money at all.
The commonest one, and the cheapest. A cable that has spent five years trapped under a cabinet door, or hanging over the edge of a counter with the weight of the scanner on it, eventually gives up inside the insulation where you cannot see it.
A cable is a part, not a repair. It comes off and a new one goes on, and on a scanner somebody was about to throw away that is usually the whole story.
A worn trigger switch shows as intermittent scanning — the laser or the imager only lights up sometimes. Pull it and watch the front of the scanner rather than the screen.
The real tell is behavioural. If you have found yourself squeezing it four times, or tapping it on the desk to get it to fire, that is the trigger and no cable will fix it. Most people recognise themselves in that sentence.
On a cordless scanner the pack is what fails first, and the way people work around it is worth describing properly — because it works, and because it is not a fix.
Watch a busy checkout when the scanner freezes. The operator pulls the battery out, shakes it, puts it back in, scans the pairing barcode on the base station, waits a few seconds and carries on — fast enough that the customer in front never quite works out what happened.
It works, and not for the reason it looks like. Taking the battery out is a hard power cycle, and the pairing barcode re-establishes the Bluetooth link to the cradle. The shake does nothing. Reboot and re-pair is the whole trick, and it is worth knowing because you can do it deliberately instead of hopefully.
And it is a stay of execution, not a repair. It buys the queue. The problem comes back, usually soon, because the pack is old — these scanners are typically several years into being worked twelve hours a day, seven days a week, and handled roughly. Replace the battery. If a new pack does not fix it, the scanner itself is done.
Why the pairing barcode lives on the cradle. It has to be somewhere you can point a scanner at while you are holding the scanner, and the base station is the nearest flat surface there is. On Zebra cordless scanners that is where you will find it. If the cradle has gone missing, the same barcode is in the product reference guide — and we have most of those on file.
This is the part most suppliers will not tell you, because the honest answer loses them a repair job.
Cheap, quick, and often something you can fit yourself. If a worn cable is the fault, replacing it is obviously worth doing on any scanner still earning its keep.
Also a part rather than a repair, and the thing that brings most cordless scanners back from the dead.
That is a repair, and a repair has labour in it. A barcode scanner under about $500 is close to a disposable item — the assessment, the freight and the labour come to more than a new one costs, and the new one arrives with a warranty.
It is also what actually happens if you try. Most online resellers will not handle it at all — they pass you back to the manufacturer to quote, and you find out in three weeks what somebody could have told you in a sentence.
All of the arithmetic above assumes it is your money. If the scanner is still inside its warranty it is not, and the answer changes completely. Tell us when you bought it before anything else.
The same arithmetic runs on printers, with bigger numbers and the same shape. What a repair costs and when it stops being worth it is set out on one page rather than repeated here.
Last, on purpose. It is genuinely interesting and it almost never tells you why yours has stopped working.
A laser scanner sweeps a single dot of red light across the barcode and measures how much comes back. Bars absorb, spaces reflect, and the pattern of those changes is decoded into the number. It reads one line at a time, which is why it wants to be roughly square-on and why it cannot read anything printed as a square.
An imager takes a picture and decodes it in software. That is why it reads QR codes and DataMatrix, why it reads a barcode upside down or at an angle, and why it reads a code off a phone screen where a laser sees only glare. Nearly everything current is an imager.
Which matters far less than people expect. The mechanism is not usually the reason a barcode fails — the label, the cable, the trigger and the battery are. If you are choosing rather than fixing, what it has to read and how far away decides it, and that is answered in three questions on the scanners page.
Tell us what the label looks like, what the scanner does when you pull the trigger, and roughly how old it is. Between those three we can usually say which of the four it is without seeing it — and whether it is worth any money.
