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[HELP] CPC6128 Black screen after +12V accidental "injection"

Started by Salvo B, 11:05, 22 June 18

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Salvo B

Hello friends
Really sad to write this..
Some weeks ago I've made a mess... I was moving some things on my desk and I've accidentaly touched with the +12V psu connector the PCB of an M4 board connected to my CPC while was turned ON.
Now the machine just gives me a blank black screen (LED on)... I'm definitively not a pro on reparations, so I've just tried to replace the Z80 as I've read on the service manual (was one of the possible problems). Unfortunally this didn't solved anything.
I've no other machines for swapping chips and I'm not able to check passive components or anything else...I've already writed to the good old Duke for servicing the board (I'll send you ASAP, maybe with my CPC board), but I really need someone who can help me repairing my beloved.
Please anyone out there? Bryce? Duke himself? I can ship the board or we can do some test togheter...

Duke

Quote from: Salvo B on 11:05, 22 June 18
Hello friends
Really sad to write this..
Some weeks ago I've made a mess... I was moving some things on my desk and I've accidentaly touched with the +12V psu connector the PCB of an M4 board connected to my CPC while was turned ON.
Now the machine just gives me a blank black screen (LED on)... I'm definitively not a pro on reparations, so I've just tried to replace the Z80 as I've read on the service manual (was one of the possible problems). Unfortunally this didn't solved anything.
I've no other machines for swapping chips and I'm not able to check passive components or anything else...I've already writed to the good old Duke for servicing the board (I'll send you ASAP, maybe with my CPC board), but I really need someone who can help me repairing my beloved.
Please anyone out there? Bryce? Duke himself? I can ship the board or we can do some test togheter...
You can ship me the mainboard aswell, and I'll check it up, but beware return shipping costs is expensive from here (probably about 28 euro!).

Salvo B

Quote from: Duke on 11:18, 22 June 18
You can ship me the mainboard aswell, and I'll check it up, but beware return shipping costs is expensive from here (probably about 28 euro!).
Thanks Duke, I know about the shipping costs, thats the reason why I'm looking for other solutions!

Duke

Quote from: Salvo B on 11:20, 22 June 18
Thanks Duke, I know about the shipping costs, thats the reason why I'm looking for other solutions!
Start by feeling out if some of the RAM chips get (very) hot, its probably first thing to go with over voltage.

Bryce

You can send it to me, I'm in Germany so the postage should be quicker and cheaper.

Bryce.

Salvo B

Quote from: Bryce on 12:09, 22 June 18
You can send it to me, I'm in Germany so the postage should be quicker and cheaper.
Thanks Bryce, I'll be glad if you can send me your address in a private message so I can estimate the postage.
@Duke I believe that shipping the M4 board only will cost significatively less... I'll let you know when I can organize me...
Thanks both! :)

Bryce

Sorted :)

And the culprits were: The Lower ROM, the CRTC and the FDC765. All had failed completely, however, you're extremely lucky, everything else seems to have survived the abuse. I'll give it a full test later to make sure everything works as it should.

Bryce.



VincentGR


Bryce

Quote from: VincentGR on 19:38, 15 July 18
Another one saved!!!


BTW, someone raped a 1084  ;D

Actually it's the rebadged Highscreen version of the 1084. It was sold by a German electronics chain back in the day.

Bryce.

VincentGR

Yeah, seen that "philips - commodore" case even on acorn machines.

Bryce

Meh, not quite there yet with the repair. Sound, keyboard and tape loading are ok, but CAT gives the "Press Play then any key" line, which means that ROM 7 is dead too :( I'll swap it out later. Then just the upper 64K to test and it's back to its original state.

Bryce.

Bryce

ROM 7 swapped and upper RAM has also passed all tests, so I can declare this board as finished, now I just need to take a look at the crazy 3in drive you sent me. It spins at 565rpm no matter what adjustments you make :D

Bryce.

||C|-|E||

Quote from: Bryce on 20:04, 16 July 18
ROM 7 swapped and upper RAM has also passed all tests, so I can declare this board as finished, now I just need to take a look at the crazy 3in drive you sent me. It spins at 565rpm no matter what adjustments you make :D

Bryce.
You can install a variable resistor in there and adjust the motor with it  :laugh:

Kris

Quote from: Bryce on 20:04, 16 July 18
ROM 7 swapped and upper RAM has also passed all tests, so I can declare this board as finished, now I just need to take a look at the crazy 3in drive you sent me. It spins at 565rpm no matter what adjustments you make :D

Bryce.

I would be interested in your findings about this drive if you are successfull to fix it ;)
I still have a CPC6128 with a strange drive behaviour (measure with RPM software give results from 300 to 600 RPM on a cycling manner).
Thank you

Bryce

Quote from: ||C|-|E|| on 10:42, 17 July 18
You can install a variable resistor in there and adjust the motor with it  :laugh:
There's already one in there, it's just not doing what it should. However, the drive has a bit of a history. The lid is missing off the top and someone tried to fix, well I'm not sure what they tried, but they managed to break a corner off the PCB and rip some tracks off too, so the motors current random results isn't suprising.

@kris: With your drive you may have dry joints to the index sensor. Usually directly at the socket on the main floppy PCB. This will cause the exact symptoms you are describing.

Bryce.


Bryce

Crazy stuff... I just repaired the floppy drive, and among other things (the damage to the PCB mentioned above), the "fixer" had resoldered the power wires the wrong way around!! Despite this, it now works again! Without anything having been damaged from the polarity mix-up. They don't make things like that any more.

Bryce.

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