VG crop sensor issue

[emhmotorsports]

Hi everyone, my crop sensor seems to have recently stopped working on my VG-640. I've pulled it out, scrubbed it up with isopropyl alcohol, but no luck. When in the service menu looking at the output, I'm seeing 3.5V when over the crop mark and 2.0V when I slide a blank piece of white vinyl under it. Does anyone know what these voltages should typically be?

The fact that there is a state change leads me to believe that the sensor hasn't failed (light sensors tend to not do anything when failed), so really wondering what I have going on here... Any advice is appreciated

 

[emhmotorsports]

Sooo...it seems it will take 3 weeks to get the parts. I couldn't wait that long. So there appears to be a potentiometer on the circuit board connected to the crop mark sensor - it must adjust something! As I turn it completely one way, the voltage goes to 3.5V. As I turn it the other, voltage goes to 0V. This must be the droid I'm looking for! Being that the highest voltage I see is 3.5V, I'm assuming this sensor drives a CMOS level input circuit. The lowest acceptable level for logical '1' is 2.0V and the highest acceptable level for logical '0' is 0.8V. So I played with the potentiometer until I got 3.0V on black and 0.2V on white. BINGO! It is now recognizing the crop marks again!

If anyone is having issues with their VG recognizing crop marks, I suspect this potentiometer may be the culprit. It takes very little effort to rotate the potentiometer, so I suspect these all get out of adjustment after some period of knocking about on top of a moving cutter/print head. It also takes very little rotation to make a big difference in output. I put a piece of tape across the face of it to see if this will help it keep it's adjustment.

Ugh, this would all have been so much easier if Roland would just let me buy/see the service documentation...