Gray screen of death

[Marq]

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?

[Munchausen]

What did you do to it?! 


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?

[Marq]

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.

[ralferoo]

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.

[Munchausen]

When you say stable I presume this doesn't apply to the garbled mess on my screen (though border is stable I think)?

[Marq]

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.

[arnoldemu]

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.

[Marq]

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.

[protek]

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.

[Marq]

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.

[fuselage]

 Hello All,
 
 I found my old CPC6128 after 16 years and decide to adapt a new power supply from an old mini desktop PC. (+5V and +12V (with negative pin in the middle!))  It works! Then my next step was to adapt a 3,5” floppy disk. Also this worked really good, but only for about 10 min. Then I got the same border black and centre grey screen.
I connected LK5, LK6 and LK8 without the PAL. But still the same gay screen. I checked the INT (Pin 16) from the Z80 it is on ground, so it is high or? What can I do next? I need some help…
Fuselage
 

[TotO]

As I know, black border and grey screen mean that no ROM was found at boot.

[gerald]

As I know, black border and grey screen mean that no ROM was found at boot.

No, No, No 
That usually mean the ROM is OK and initialized the CRTC / GA ) but the ram is failing.

[TotO]

Buuuu... If I plug the X-MEM with the working RAM and unworking ROM, I got it. 
(but sure, you are probably right... don't take care about my post)

[Fuselage]

So, I checked the INT signal on the Z80 ...there is nothing. Directly after turning on the CPC there is a short high signal then low again. I checked also the interupt generator and I think there is a failure in the GA 40010. I get a Signal from the HSYNC from the IC 108 but there is no output from the 40010. I read this documentations:devices:gatearray [Grimware] last night.

[Fuselage]

Here my further experiences with the repair of my old 6128....

So, I get some spare parts frome France (thanks to Cent pour Cent!Great Service!): a GA and a Z80. I changed the GA and nothing happend, I changed the Z80 and I got a classic 1.1 basic screen again!    It was alive again! So I changed my old GA and found out, that the GA was not damaged although I get no signal from the INT to the Z80 (I posted before). Everything was fine..then...
After I connected my ext. 3,5" floppy, still happy that a |b and a cat give me some files on the ext. floppy. 2 min later I get some colorful ASCII in the screen and again after a reboot only a gray screen with a black border....
My next steps now: buy a new Z80 and looking for a good ext. floppy wiring plan....

[Bryce]

If you were able to "CAT" and see files, then the drive is wired properly. I'd be more worried about your power supply. What are you using to power the 6128?

Bryce.

[endangermice]

I presume you've got nothing you can use to test either CPU? I'm with Bryce, check your power supply before doing anything else though I would have thought the memory chips would have been fried before the CPU. Of course that may be your problem now, the power supply might be failing to supply the correct voltage at random intervals.


It's also possible that there is a bad connection on the CPU socket that you disturbed when replacing the CPU. It might be worth swapping the socket or at least checking the solder joints and the spring pins in the current socket. I'd also check the continuity between the actual pins on the CPU and the corresponding joint on the bottom of the board. Of course it's also perfectly possible that one of the board lines is also broken though I'd say this is less likely.


It's also possible that the CPU isnt the problem and that a connection issue exists elsewhere, again disturbed somehow when you swapped the CPU. Socketed components are your first port of call.

[Fuselage]

 My CPC6128 is alive again! 
Igor, bring me the video camera and don’t forget the Aspirin for my head!
 
@Bryce I´m using a switching power supply for the CPC6128 and also for the ext. floppy.
5V with max.5A and 12V with max.300mA.
 
I had a very nice and helpful email conversation with [centpourcent] and the result was:
 
CLEANING! Every socket, Z80, GA etc. and also the centronics plugs on the back and [important!] the power switch beside the volume wheel. I used WD-40 contact spay and a hard hair brush.
And now everything work perfect! Also the ext. floppy. (There was no failure in the ext. floppy wiring.)
In addition I use the “old” chips again, so no one was burned, just bad contacts.
Thanks to all helpers and this great forum!

[Bryce]

Aaarrrgh WD-40 is NOT a contact spray! It's a water displacer for loosening rusty bolts and will mess up these old switches in the long run. Always try to use a real contact cleaner when cleaning retro parts.

Switchmode supplies have their advantages, but may also be the cause of random crashes or other problems due to the fact that they are relatively noisy. If you've no problems, then all is ok, but if you do get problems, always revert to a linear supply to see if that solves them.

Bryce.

[Vuselage]

Sorry forgot my password and waiting for a mail to reactivate my account.. so Vuselage
Everything is safe...
Here in Germany we can buy a special contact spray from WD-40, it was not the classic once I use normaly for cars.
Search: WD-40 Specialist 11 oz. Electrical Contact Cleaner Spray
My Apple IIe and Ti99-4A are loving this spray! And it is very soft to all plastic...

But you are right, the switching power supply is not the best choice. After a hole day I got a fancy screen again and now again gloomy gray.....
So building a classic copper monster...

[Bryce]

Ok, the name "WD-40" confuses, most people associate that with the original WD-40, better to just say contact spray.

You've swapped between "Fuselage" and "Vuselage", maybe that's what's causing your Password problems?

Bryce.

[Vuselage]

Yes, something went wrong with my account or better my password.
Yesterday I create an account and my second try to log in failed due to the password... strange. I allways get the message that my wasspord is wrong...
I can not log in and I´m waiting since yesterday for an e-mail with a new login password. I want to answer your mail...

[TFM]

Did you recently change your PW? Then try to use the last version. Or ask Gryzor for help. 

[Bryce]

He only joined 3 days ago.

Bryce.