CPC464 no sound

[SilverGreen93]

Hi,


I just purchased a Schneider CPC464 at a really good price, but it was in the worst shape ever (will make a picture/review/restoration topic later).
I just finished cleaning all the parts, washing, dusting etc and the main board seems to be working, the keyboard is working, the screen is ok.
However, by testing the "DEL, DEL, DEL" press, I am not receiving any sound from the internal speaker. I cannot test the cassette interface because I have a bad belt and missing rubber piece on the drive wheel which I cannot seem to find a replacement for.
I traced the wiring to the speaker and it seems ok, the speaker itself is good, measured about 8 ohms.


So, I used an oscilloscope to take a look at the AY output (pin 1, output C, the other 2 have the same output) when pressing DEL key and here is the waveform attached. In my opinion there is something there, but the signal seems too low. I don't know if that's good or not as amplitude and frequency.
Do you have any suggestions where should I look next? Is the AY chip good? (The SOUND pin on the tape connector has a very similar waveform)


Thanks,
Mihai

[Bryce]

My first guess would be that the AY has died. Have you tried connecting the audio out to a set of powered PC speakers? If nothing comes out there, then the AY is definitely gone.

Bryce.

[SilverGreen93]

Thanks for reply. I will check that and come back.
Do you have a sample waveform from a working AY to compare? Still, I see that the AY is doing something...
Is there anything else to check before I order a new AY chip?

[SilverGreen93]

I've tested the output from the 3.5mm stereo jack through amplified speakers and it sound good. The "DEL, DEL, DEL" test passes.
In this case seems that the AY chip is not faulty. What to do next?

[Bryce]

Then you need to follow the signal... Check the connections to the tapedeck, then the input of the amplifier and the ouput of the amplifier.

Bryce.

[SilverGreen93]

Ok, I found the solution: The C309 on the cassette desk was faulty and the signal did not pass through. I replaced it and I have sound now.
Question: The sound seems to be a bit low. How loud should it be at max volume?
Also when using the SAVE command the sound is very low and I can't seem to save or load anything from cassette. Nothing can be heard from the tape deck when using LOAD or RUN. Is it something else wrong?

[Bryce]

Yes, there's a good chance that IC302 is damaged then. It's the only part that is used by both the sound and for amplifying the load/save signals.

Bryce.