Dead CPC 464

VincentGR · 22:30, 29 March 19

So it was dead while the dude sold it as working.
Anyway, I got 4.78V at pin 8 on RAM chips, swapped them with new in sockets just in case.
Z80, 40010 work, tested them on my 6128.

The screen is black but sometimes I have this:

https://www.youtube.com/watch?v=8fRuy6nQ_74

The flickering is NOT from my camera, this is what you get in real life.

Thanks in advance.

tjohnson · 08:56, 30 March 19

Video not working

VincentGR · 09:46, 30 March 19

Quote from: tjohnson on 08:56, 30 March 19
Video not working

Oh, is it now?

ComSoft6128 · 09:52, 30 March 19

It's working on YouTube but not via the Forum.

Cheers,

Peter

Bryce · 12:39, 30 March 19

Stick a scope on pins 39 and 40 of the CRTC and see if it's producing sync signals. If one of the is missing then the CRTC is bad.

Bryce.

VincentGR · 12:55, 30 March 19

I don't have a scope Bryce, I've only tested the voltage on CRTC too.

Bryce · 16:45, 30 March 19

Then measure the voltages on the two pins.

Bryce.

VincentGR · 18:29, 30 March 19

Yes I only did that, 4.9V.

Bryce · 19:52, 30 March 19

4.9V on the sync pins? Or is that the supply voltage? Pins 39 and 40 should be giving V and H sync signals. Both are active high, so you should be reading a lot less than 4.9V. Try measuring them with the multimeter. If they are very close to 5V or 0V, that could indicate an issue.

Bryce.

VincentGR · 14:30, 01 April 19

Pins 1 and 20 have 4.9V.
39 and 40 0.12V...

Bryce · 14:35, 01 April 19

That sounds reasonable. Possibly a 74LS153 has failed?

Bryce.

VincentGR · 15:22, 01 April 19

8 -16 gives voltage? 5V?

Bryce · 07:38, 02 April 19

Quote from: VincentGR on 15:22, 01 April 19
8 -16 gives voltage? 5V?

On what chip? If it's the CRTC then you have an issue. Pins 14 and 15 aren't even connected to anything!

Bryce.

VincentGR · 08:50, 02 April 19

I was talking about 74LS.

Measured all chips on board, voltage is ok.
Dunno, I might swap crtc and rom

Bryce · 09:01, 02 April 19

Measuring supply voltage only tells you that they're getting power and that they don't have a major short circuit. But don't just swap things for the sake of it. It could be a simple trace break or bad solder joint.

Bryce.

VincentGR · 17:05, 02 April 19

So re soldered all connections and checked every line, nothing.
Swapped CRTC to another machine and worked.
The last chip is the ROM.
I hope this is it because then I'll have to replace LS chips

VincentGR · 15:13, 03 April 19

Good news everyone!!!

AMSTRAD 40009 => Dead
1x RAM IC => Dead

CPC is working

Thank you all.

gerald · 16:36, 03 April 19

Quote from: VincentGR on 15:13, 03 April 19
Good news everyone!!!

Uh-oh, I don't like the sound of that.

VincentGR · 16:59, 03 April 19

Lol.

With a dead ram ic, I had the same screen like with a dead Z80.

BTW is there a post with faulty screens here?
If not we must make one with photos and possible problems.

Bryce · 08:03, 04 April 19

I'm not sure that a faulty screen page would help that much. The CPC isn't like a C64 which has about 10 different screen "clues" to the failure, it has only three or four and all of them can point to multiple things:

- Completely blank screen - Possible problems: Power, CPU, GA, CRTC, clock circuitry, reset circuitry, broken trace, short circuit. In fact almost anything on the PCB or PSU.
- Blank screen with square in the middle - Possible problems: CPU, CRTC, RAM, Multiplexer IC's, ROM IC, buffer IC's, broken trace.
- Non-synced screen (what you had) - Same as above.
- Screen that stops just before the ready prompt appears - AmDOS ROM or any part of the disk system.

Bryce.

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Dead CPC 464