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avatar_llopis

Accurate circuit diagram for different 464 PCBs?

Started by llopis, 22:59, 09 August 18

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llopis

I'm tracking down an issue with some non-working keys on a CPC 464 with a version 3 board, and so I'm looking at connectivity issues between the keyboard connector, and holy Batman, it doesn't look anything like the circuit diagram in the official CPC 464 book!


The AY pin 7 is not connected to both pins 8 and 9 in the keyboard connector. It actually isn't wired like that at all! It's wired like a 6128 (see second attachment).


OK, so maybe this kind of board is wired completely like a 6128? Noooooo... the 74LS145 (IC101) is mostly wired like a 6128, but pint 11 on the decoder goes to pin 1 on the keyboard connector!


As a matter of fact, even the PCB is misleading. The keyboard connector is labeled as an 18-pin connector, not 20!


To make things even more fun, I looked at the circuit diagram of the CPC 664 and it's different yet again!


What is going on here? Why is this part of the PCB so much in flux (it seems like a super straightforward part) and where can I find an accurate one for a version 3 board?

Audronic

@llopis
Here are 2 More from the Amendment Service Manual.
Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.

llopis

Thanks! I had missed that manual completely.

Audronic

Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.

llopis

Embarrassingly, it was something much simpler: the keyboard ribbon connector on the PCB needed some cleaning. Once I did that, everything worked like a charm. But this is all super useful info I'm archiving for future repairs.

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