Author Topic: Gray screen of death  (Read 3906 times)

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Offline Marq

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Gray screen of death
« on: 17:37, 01 February 13 »
I'm continuing my efforts with the fried CPC 6128 and have confirmed that at least that the 40010, the CPU and the small socketed chip that says "PALandalotofnumbers" are all fine. All I'm getting is an empty gray screen with a black border. Is this some symptom of a well-known failure in, say, the boot process?

Offline Munchausen

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Re: Gray screen of death
« Reply #1 on: 18:01, 01 February 13 »
What did you do to it?!  :o


I have a fried CPC6128 somewhere... I accidentally plugged 12V into it instead of 5 (was using the 12V line to power a small LCD and got the lines swapped - :( - wont make that mistake again). Now all it displays is a garbled mess of green and pink with a blue border, IIRC. No idea what's wrong with it, it doesn't make a beep when you press del and it doesn't make any sound from the disc drive when you type "cat" so I think it's very dead. Suspect ROM and/or RAM and probably other stuff too.


Considering some of the parts are impossible to get now I figured it would be easier to actually replace the whole thing than try to fix it. I did find that you can get RAM on ebay for an extortionate amount, and the ROM can probably be replaced if you can source an EEPROM programmer.


Good luck though, if you get it working I'd be interested to see if I can resurrect mine! What did you try so far?

Offline Marq

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Re: Gray screen of death
« Reply #2 on: 18:12, 01 February 13 »
My 6128 died under very similar conditions: I powered it with 9V that I happened to have set to a transformer after using a Spectrum earlier. Initially it produced a pink/blue screen but now it has turned into gray/black. I've swapped the 40010, the CPU and the PALsomething between the corpse and a working 6128 and confirmed that they are ok. I probed the CRTC a bit and it seems to give something sensible-looking out. Starting to suspect a memory failure, but couldn't find any hot RAM chips so far.

Offline ralferoo

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Re: Gray screen of death
« Reply #3 on: 18:26, 01 February 13 »
If you're getting a stable screen with a border, then you know that the CPU, ROM and CRTC are all working correctly and at least some of the gate array is working too. Which pretty much leaves only a RAM issue or damaged PCB tracks as the culprits. "RAM" is more complicated than just the RAM chips - I've also had a CPC where one of the the memory address line multiplexors was fried.

Offline Munchausen

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Re: Gray screen of death
« Reply #4 on: 18:30, 01 February 13 »
When you say stable I presume this doesn't apply to the garbled mess on my screen (though border is stable I think)?

Offline Marq

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Re: Gray screen of death
« Reply #5 on: 18:52, 01 February 13 »
If you're getting a stable screen with a border, then you know that the CPU, ROM and CRTC are all working correctly and at least some of the gate array is working too. Which pretty much leaves only a RAM issue or damaged PCB tracks as the culprits. "RAM" is more complicated than just the RAM chips - I've also had a CPC where one of the the memory address line multiplexors was fried.

Thanks, this at least gives some pointers as to what to try next. I guess I could measure the voltage going to the memory chips next before starting to gauge them out. At least it would be very useful to detect which one has died.

Offline arnoldemu

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Re: Gray screen of death
« Reply #6 on: 19:38, 01 February 13 »
I'm continuing my efforts with the fried CPC 6128 and have confirmed that at least that the 40010, the CPU and the small socketed chip that says "PALandalotofnumbers" are all fine. All I'm getting is an empty gray screen with a black border. Is this some symptom of a well-known failure in, say, the boot process?
I've seen something similar when the PAL doesn't work correctly.

you can put in some wires to disable it and connect them into the socket. I can't remember the connections, but look at the schematic.

on reset, the gate-array will set the border to black and leave all the other colours unchanged. so this explains why the border is black.
the size of the screen indicates crtc is ok.
it's grey, seems to indicate the rom is mostly ok.

check the int line on the z80 is not stuck, or at least the gate-array is clearing the int, if it's got stuck it's looping over the same thing again and again.

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Offline Marq

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Re: Gray screen of death
« Reply #7 on: 19:49, 01 February 13 »
I've seen something similar when the PAL doesn't work correctly.

you can put in some wires to disable it and connect them into the socket. I can't remember the connections, but look at the schematic.

on reset, the gate-array will set the border to black and leave all the other colours unchanged. so this explains why the border is black.
the size of the screen indicates crtc is ok.
it's grey, seems to indicate the rom is mostly ok.

check the int line on the z80 is not stuck, or at least the gate-array is clearing the int, if it's got stuck it's looping over the same thing again and again.

I put in a PAL from a working machine and nothing changed. In addition I swapped the suspect PAL to the working 6128 and it still worked. Could check the interrupt line, though.

Offline protek

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Re: Gray screen of death
« Reply #8 on: 08:46, 07 February 13 »
My 6128 died under very similar conditions: I powered it with 9V that I happened to have set to a transformer after using a Spectrum earlier.
Was it just the voltage or was the polarity also wrong? Spectrum has a negative center pin, you know. Don't know if it makes any difference in the troubleshooting but I thought I'd mention it.

Offline Marq

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Re: Gray screen of death
« Reply #9 on: 09:41, 07 February 13 »
Was it just the voltage or was the polarity also wrong? Spectrum has a negative center pin, you know. Don't know if it makes any difference in the troubleshooting but I thought I'd mention it.

I don't quite remember how the polarity was. Probably I changed that but forgot to change the voltage.