Thermal ticket printer repair, doesn’t detect paper, optical sensor

[Chungalin]

This is from a professional scale RM-50 EL(M5), Gram Precision brand. It always complained out of paper.

There's a small optical sensor at paper path that detects it. It's a reflective sensor consisting of an IR LED plus a phototransistor. It detects anything white at 1mm distance.

First I thought that it was just dirtiness (it's from a butcher shop), but cleaning didn't improve. I made a bridge between phototransistor Emitter and Collector to defeat paper sensing while the replacement gets here.

After a lot of research, I deducted that original sensor was a Panasonic CNB10010xL (CNB10010SL for instance). While this sensor is obsolete, I found that Fairchild QRE1113GR is highly compatible. The only difference is flat corner placement in package.

Today I've changed it and it works OK.

[stj]

Re: Thermal ticket printer repair, doesn't detect paper, optical sensor

probably a weak led. you could have checked that with your phone camera.

[Chungalin]

Re: Thermal ticket printer repair, doesn't detect paper, optical sensor

Man, believe it or not, I tried that to no avail. I couldn’t deduct if the bad part was the LED or the phototransistor. With original bad sensor, I tried:

1) "Shoot" IR light directly to the phototransistor from a remote control. No reaction at output.
2) Tried to see IR light with a camera. Nothing.

Now, after replacement, I’ve tried the second thing again. Nothing at all. Perhaps the light is so faint that it can’t be detected by phone camera. It can see other IR light, like remote controls, but I never use it for diagnosing remotes.

[stj]

Re: Thermal ticket printer repair, doesn't detect paper, optical sensor

maybe the led is focussed to a sharp point in a specific direction.

[keeney123]

Re: Thermal ticket printer repair, doesn't detect paper, optical sensor

Do you have a schematic to the printer? Are you getting a 0.7 voltage drop on the anode cathode of the photo optic IC? This will tell you in which side the problem is. What are the symptoms of the printer?

[Chungalin]

Re: Thermal ticket printer repair, doesn't detect paper, optical sensor

Thanks keeney, but the problem is already solved by replacing the photo sensor with an equivalent. The printer is already assembled and ready to return to customer. I won’t do further checks.

The symptom is described in thread title: "doesn’t detect paper", always says "out of paper" error. I made a bridge between phototransistor E & C, and the customed used it for two weeks until I got the replacement sensor. I told them to everyday check the paper reel so it didn’t run out of it and force the feed gears.