Beolab Penta MK3 displays dead

[Regenpak]

Veteran electronics engineer but first time poster here, hailing from Amsterdam. A good friend and B&O fanatic has four Penta mk3 displays that are all four dead. He sent them to me and because I have no B&O equipment I created PIC software (PIC12F683) to emulate a Beolink command. I did quite a bit of research online and found information to build a test command. I also compared it with the command from my friend’s Beocenter, and they were equal. Still no luck. Grounding the test pin (#36) of the micro makes the 12 characters show 12 times I-H-#-$ so the micro seems to be OK as is the display board with the alphanumerical displays. I am out of inspiration about what could cause the four displays to go dead. Power is OK, all capacitors have been replaced earlier on.

How do I fix these displays?

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[Regenpak]

I just realized something. The AUDIO/!VIDEO input is HIGH to unblank the display. When LOW in case of home theater it blanks the display but if the input has gone phut and always reads LOW for the firmware inside the 80C52 the display will never get unblanked. So if that is actually the case all four units are toast. There is current flowing out of pin#25 but being TTL that is always the case.

To troubleshoot further I will do some supply current analysis. If there is any processing going on this will show in the current going into the VCC pin #40.

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