CPC 464 no signal on monitor

Josip · 20:52, 19 February 24

Recently got another CPC464.
Motherboard is MC0046A, Z70378

First there was no power at all, but it was some damaged traces on power jack, sorted this and replaced connector.
I got power but nothing on monitor, not signal at all.

Tried to swap CPU but same problem, checked some clocks and seems to be ok, got 16Mhz on 40007, reset seems ok (high when i press reset goes low than high again).

Only chip that is hot on touch is 40007, maybe he can be culprit?
Also with 40007 in place there is significant voltage drop, getting aroung 4.65V, without chip around4.9V
This is somehow is point me that 40007 is bad?

Done some googling but cannot find nothing helpful.

Can bad ROM cause nothing on screen, that chip i can easly replace with eprom.

Only GateArray and CPU are socketed.

Bryce · 21:22, 19 February 24

Hi,
I'd start by checking the solder joints and traces to the monitor socket and clean the socket contacts too.

Bryce.

Josip · 21:51, 19 February 24

Solder joint looks good, also sockets, no sign of corrosion.Video jack have good grip.

Bryce · 09:06, 20 February 24

Have you any equipment to measure the signals on those pins?

Bryce.

Josip · 10:16, 20 February 24

Yes i have oscilloscope.

Bryce · 11:06, 20 February 24

Then check if there are signals on R, G, B and Sync. And check the same on the monitor side, the spiral cable is known to break inside.

Bryce.

Josip · 11:38, 20 February 24

I do not have original monitor.
Will check those signals

Josip · 20:16, 20 February 24

Ok, tried with dandanator, checked on mine working cpc what need to be pressed.
As i can hear, games starts, i can hear sound over speaker, seems that computer works ok, keyboard reacts because i can start game.

So probably CRTC is dead?

Bryce · 21:00, 20 February 24

Not necessarily, the Gate Array is what actually produces the monitor signals. Check pins 39 and 40 on the CRTC with your scope. They should be producing the H and V-Sync. If they are missing, then it's the CRTC that's bad. If they are there, then it may be a gate array problem. Of course, if you have a second CPC with the same GA, then you can just swap the chips as they are socketed and see if the monitor output works with a good GA.

Bryce.

Josip · 08:10, 21 February 24

I have on order new gate array and CRTC, should arrive in next few days, so will see what is the issue.

Josip · 18:25, 28 February 24

Gate array replaced, machine is live again.

Thanks for help.

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CPC 464 no signal on monitor