AMSTRAD CPC6128 power up failure

[rpalmer]

Of course you can check it even easier: Just short the reset pin to ground for a second, if the CPC boots properly, then the reset circuitry isn't doing its thing at startup.

Bryce.

Also this seems quite contrary if cpc boots properly then how can reset circuitry be faulty? Did you mean if boots okay then reset is okay?

rpalmer

[Bryce]

The reset circuitry is only used for a cold start (power switch start). Shorting the reset line to ground would "re-synchronise" all the ICs and doesn't use the reset circuitry. Either way, if the short trick didn't make a difference, then the reset circuitry is probably fine.

Have you tried swapping the ROMs yet?

Bryce.

[rpalmer]

bryce,

I have tried swapping the roms and again no difference.

rpalmer

[Bryce]

There must be a broken trace somewhere on the PCB. There's nothing left that could be causing the issue.

Bryce.

[rpalmer]

thats something I have come to the same conclusion and will likely take some time to find.

rpalmer

[Bryce]

My guess would still be that it's somewhere around the ROMs.

Bryce.

[Audronic]

Ray P


The traces that I have found that were Open or Hi Resistance were not the same colour as the rest of the traces (Slightly Blackened).
This may be of some help, it may be easier to have a look first, than testing literacy hundreds of traces ? ? ?.


Ray W

[Bryce]

Then you may never get it running reliably. That's copper oxide under the silkscreen, happens when the computer has been in the damp for a long time. I tried fixing an SMS II with the same problem recently, but it got to a stage that it just wasn't financially worth continuing.

Bryce.

[rpalmer]

A little update from previous post.
I have finally socket-ted all of the chips on the motherboard (except for the 74LS27 and SED chips). These chips are party of Disk controller, so have assumed they dont impact the main CPC circuit.
I still have no joy after finally replacing the AY-3-8912 (thinking that maybe the 'CPU' signal from the Gate Array was somehow being affected by the AY-3-8912 and hence affected the 4 74LS153 chips for CPU/CRTC address select. The CPU line from the Gate Array is a 1MHz clock for the AY-2-8912 and is fed into the 74LS153 chips.

I now suspect there is something deeper in the PCB itself which is the issue (and suggested by the others).
Attached is the picture of the state of the motherboard. In the picture the RED means NEW chips, Orange means replaced capacitors, yellow means chips checked on a working CPC6128 and showed no problems.
rpalmer

[vasilisk]

I am no expert in cpc repairing, or repairing in general. What are these two connections for? (blue circle in attached image)
Just asking, because I have two 6128, different versions, and neither of them have these. I dont know if they are related with your problem. Just pointing it out.

[rpalmer]

vasilisk,
They are the links to define what is shown on power up/reset (namely Arnold/Awa/AMSTRAD/Schenider).
rpalmer

[vasilisk]

Thanks for the info. Hope you find the problem, since you replaced almost everything.