HP-65 1605A02841 - weird display and card reader issues

[teenix]

(11-14-2020 12:16 AM)albertofenini Wrote:  Hi Everyone,
this an update of an older post, basically this unit has an hybrid pcb and a keyboard/led pcb with this issue :

When used with its own hybrid the display turns on the requested segments for the requested digits PLUS all the decimal points and all the C segments

When used with any other different (known working) hybrid the display turns on the requested segments for the requested digits PLUS the decimal points
and the C segments for the digits actually used plus the one after the last one

I think the pictures will better describe the situation

All of the waveforms have been taken using a known working hybrid logic board

Quite surprising all the waveforms are of the correct form and value

What could it be the problem ?
There are no open coils but we don't know how to test if some coils are shorted together

Unluckily we have not taken the waveform for Anode segment C when it should not be on, like when the display is showing a 2

Thanks in advance for any advice !

Pictures : HP-65 1605A02841 - wrong display behavior

All DP LEDs on indicate a low battery voltage condition.

If the batteries and Vbsw on the anode driver are ok, then the 220K resistor near the anode driver may be open circuit or faulty.

cheers

Tony