HP-65 goes on hold after reading a card

[albertofenini]

Hi Tony
We did it in the past and it worked out so they are compatible

However, we did the following right now :
Replaced the HP65 sense amplifier with one from a working card reader for HP41
The test sorted out the same results, WA good WB dirty
We then excluded the card reader on the HP65 de-soldering WA WB pins where the card reader interconnect the logic board
Same as before WA good WB dirty
Looked like we found the culprit in the CRC right?

Well we put this logic board in another unit and while the display fault was consistent (all g segments on) the read and write operation was perfect

This would exclude the hybrid ....

We tried the opposite, we put a known working logic board in the faulty one and the display was acting crazy with random zero’s appearing

Since it’s also Tuesday 17th ... we immediately took the good logic board out

In summary if this board in an other Unit works, and in this even isolating WA WB from the card it doesn’t... where could it be the trick ?

I would not say traces on the logic because if this was the case it would have been consistent across different units, the sense amplifier has been changed twice and this one is known to be working ...

Card reader pcb has been tested and it is very clean ...

What are we missing ?

Thanks and take care !!!