HP-67 1705A01636 [RB lower than RA, doesn't read but writes]

[albertofenini]

Hi everyone

this is a similar case to the one described in the post "HP-67 1706A00901 card reader test"
The unit is working but is not reading cards
We used the same procedure and measured CA/RA and CB/RB
Apparently CA/RA are good, CB is good, while RB seem a little low ...

Any suggestion will be greatly appreciated

Thank you very much and Take care !

Pictures : HP-67 1705A01636

[teenix]

It could be faulty sense chip RB output or CRC chip RB input if this is still connected.

It would be hard to determine which is which even if you isolate the RB pin, test again and the signal returned to a normal amplitude.

Swap the CPU board for a known good one and test again. If it works, the CRC chip RB input is probably faulty.

If the signal is still low, swap the sense chip, or board for a known good one and try again.

The capacitor on HBC would seem ok because the sense chip is detecting and conditioning the signals from the card.

cheers

Tony

[albertofenini]

Hi Tony

thanks for the reply,
I haven't swapped the CPU board yet,
but I have written a very simple program and recorded on a card
It was successfully written and successfully read on a known working HP-67
However It can be read on this unit ...

take care and thanks again !

[albertofenini]

Hi Tony Hi everyone

swapping the CPU has proven that everything else work as it should
I have captured RA and RB with the original CPU board and with a known working one
Although the don't look too different to me, as a matter of fact they are ....

This is the third case where the CPU board (I would imagine the CRC since everything else work)
is responsible for the malfunctioning

Other than buy the beautiful HP67 board replacement from Tony (which I will do anyway)
what can I try ?

Could it be a cold joint between the CRC and the board or a dirty trace ?

Thanks for help, take care !!

Updated pictures here : HP-67 1705A01636

[teenix]

(11-21-2021 03:48 PM)albertofenini Wrote:  Hi Tony Hi everyone

swapping the CPU has proven that everything else work as it should
I have captured RA and RB with the original CPU board and with a known working one
Although the don't look too different to me, as a matter of fact they are ....

This is the third case where the CPU board (I would imagine the CRC since everything else work)
is responsible for the malfunctioning

Other than buy the beautiful HP67 board replacement from Tony (which I will do anyway)
what can I try ?

Could it be a cold joint between the CRC and the board or a dirty trace ?

Thanks for help, take care !!

Updated pictures here : HP-67 1705A01636

With everything assembled, you could measure a CRC pin to the corresponding sense IC pin with an ohmmeter. You should measure 0 ohm or very close.

If it is the CRC chip, then the signals may look the same, but are not being processed properly.

I wonder if temporarily connecting a 100nF capacitor across the CRC power pins would help. That would be Vss [2] and Gnd [28]

Otherwise, only swapping the CRC chip would prove the problem.

cheers

Tony