HP-67 - 1612A03018 - Card Reader Advice Requested (was HP-67 - strange behavior)

[teenix]

(09-18-2019 09:34 PM)albertofenini Wrote:  ciao Tony,
How can we identify the fault then ?
Would you suggest to replace all of them ?
Would an HP97 be a possible donor ?
Last, sorry for all these questions, what could we compare between a working unit and this one in
order to find out what could be possible wrongs (voltages, waves ?)
Thanks again to everyone !

It could be a difficult one, I wish I could pull a rabbit out of the hat :-)

If it is a ROM problem it would try replacing ROM 0 or ROM 3. My first try would be ROM 3 (smaller - easier to replace).

However, it may not be a ROM issue as such. It could be a problem with a component (cap, resistor, diode etc) that "changed" after being cleaned and has upset the works.

Firstly, I would go back to things you have tried in the past and run your CRO over the board and see that clock signals appear to work ok, and power supply voltages are good. It might be something simple like a poorly operating capacitor.

The HP-97 ROMs are a different kettle of fish. They have the printer code embedded as well as other changes, different keyboard etc.

cheers

Tony