Cpc 464 keys not working

Circusvoltaire · 17:46, 28 January 24

Hi guys, I'm Davide from Italy and I'm a new member. I bought a used 464 but none of the buttons work...I opened and cleaned the membrane and the small springs but I didn't solve the problem. What do you think went wrong?
Thanks so much!

Rabs · 17:56, 28 January 24

Quote from: Circusvoltaire on 17:46, 28 January 24Hi guys, I'm Davide from Italy and I'm a new member. I bought a used 464 but none of the buttons work...I opened and cleaned the membrane and the small springs but I didn't solve the problem. What do you think went wrong?
Thanks so much!

Welcome, Davide, hopefully you can get it fixed.

Circusvoltaire · 18:06, 28 January 24

Quote from: Rabs on 17:56, 28 January 24
Quote from: Circusvoltaire on 17:46, 28 January 24Hi guys, I'm Davide from Italy and I'm a new member. I bought a used 464 but none of the buttons work...I opened and cleaned the membrane and the small springs but I didn't solve the problem. What do you think went wrong?
Thanks so much!
Welcome, Davide, hopefully you can get it fixed.

Hi Rabs thanks so much for your help!

Rabs · 18:14, 28 January 24

No problem.

There are loads of people on this forum with far more experience than me, so think you are in the right place.

Circusvoltaire · 18:15, 28 January 24

Quote from: Rabs on 18:14, 28 January 24No problem.

There are loads of people on this forum with far more experience than me, so think you are in the right place.

Rabs · 18:24, 28 January 24

So guess the CPC powers on ok to the Ready prompt but none of keys at all work?

Common faults include a faulty AY-3-8912 PSG, but I have also encountered faulty 8255 PIOs. Problem is fixing both of these involves desoldering and replacing the the faulty ICs. So hopefully it's something to do with the keyboard membrane.

Often with faulty AYs and PSGs you see random text appear even without the keyboard connected, like this. Do you see anything like this?
You cannot view this attachment.

Circusvoltaire · 18:27, 28 January 24

No Rabs, i can't see any chars on screen, also with keyboard disconnected..

Circusvoltaire · 19:34, 28 January 24

Rabs I was following your advice and while I was measuring the pins of the 8255 I saw corrosion on the pins!

Rabs · 20:00, 28 January 24

Well that's not good. Could be the issue. Good luck.

Circusvoltaire · 21:40, 04 February 24

Hi Rabs, thanks for your help!
you were right, it was the 8255 with the corroded pins!
This is the repair video :

https://www.youtube.com/watch?v=46CTAw54tA8

Rabs · 22:09, 04 February 24

Well done, nice video. As you can see from my dead IC pulls its normally the AY.

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Cpc 464 keys not working