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CPC 664 black screen : dead crystal oscillator ?

Started by reno, 01:18, 28 April 23

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I've just bought a 664 that shows no video output.

I checked voltages at the CPU, RAM and AY : 4.3V
Then with a scope I checked the clock signal at pin 6 of the Z80 : nothing periodic ! Ahaa interesting !
I'm new to this scope and wasn't 100% sure I was getting the settings right, but I have another 664 I can compare with and I did get 4Mhz there, so something definitely wrong with the broken one.
So I checked the crystal oscillator : getting 16Mhz on the working 664 with (IIRC) 1Vpp, and nothing at all on the broken one.

I'm not sure what to do next : is the crystal dead for sure ? Or something else that feeds it ?
The tracks don't look great in this area (actually the whole board is like that), but I've got continuity to the next components.

Any help appreciated !
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Have a look at my Black Screen 664, hopefully you don't have as many problems as me. I spent a long time tracing and fixing tracks. 


The absolute minimum voltage for most of the CPC's IC's is 4.75V. So if you only have 4.3V it's highly possible that many chips aren't doing what they should. Get the voltage fixed first. Most likely dirt on the input socket or power switch.


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