Weird CPC664 Fault

[Bryce]

Pin14 is the 5V supply on the 74HCU04. The schematic is wrong. The correct pin is 8 as far as I know. So your scope measurement was on Pin14? If so measure the voltage on startup at some other point on the PCB (Z80 supply pin perhaps?) and see if the same dip can be seen. If the dip is only around the reset chip area, then something there (most likely a TTL chip) has a failed gate that shorts to GND when the input goes high or it's output is connected to a TTL chip that has an input shorted to GND.

Bryce.

[Audronic]

Hi Bryce

Thanks 

yes it was the power line ??

I have also Replaced the IC 110 74Ls132 and I have replaced the 0.1Mf cap C128 The timer cap with a 0.2 Mf cap
Thats all I had available. and Now it sort of works 
This is weird machine

If I replace the ROM-PC IC103 with a 40009 I am able to at least get a box with white screen.
But if I put the original in 40022 Intermittent Nothing.

Hmmmmmmm

Thanks

Keep safe

Ray

  

[Brocky]

id check around the buffers in/outs..
ls244 and ls373..