HP82104A Card Reader repair - help needed

[Rsponholtz]

Hi everyone,
I was emboldened by all the information on repairing the HP82104A card reader (youtube video, article, etc) for the HP41C calculator, so I dived right in. Things went fairly well and I used the proper silicone tubing for the wheel and rebuilt the coupling. After putting things together enough to test, the reader pulls the card through, but immediately after the card starts moving, the calculator says "CARD ERR". Thinking this was a card I wrote about 20 years ago, I took a new card and did a "XEQ WSTS" which seemed to complete ok. When I try to read that card back in, I still get a "CARD ERR".

I used my multimeter to check the actions of the photodiode and the little switches, and everything seems to be working fine - looking at the white circuit board I get continuity on the rightmost two contacts when I push the card in far enough to make contact with the first switch. I get continuity on the third and fourth contacts from the right after the card moves a bit (i.e. hits the second switch), and I get about 6 volts between the last two contacts when the card is moving - this appears to be the signal from the photodiode.

So now I'm a bit stuck. I've looked at the service manual here, and it appears that I need the ET-11966 service module to make progress directly with the calculator-based troubleshooting.

I tried fiddling with R5 a bit to see if changing the speed of the motor might help. The speed of the card motion did change, but I still got "CARD ERR" every time.

Anyone have ideas on what the problem might be, or how I can debug the problem?

BTW here's what I have on-hand to tackle this:
41CV and a pack of old magnetic cards
a good multimeter
a Tek 465 oscilloscope (very old & non-storage),
a function generator, frequency counter and a power supply
some PCs (obviously)
I also have a couple of raspberry PIs and an Arduino that might be able to lend a hand :-)

Also, does anyone have a source for the actual PDF of the service manual?

Thanks for your help!
Ross