Amstrad CPC464 motherboard

[Acsi]

Why did I get myself into this... I think because through hole tech is my limit and I really enjoy getting things working again.

Anyway there was a untested CPC464 motherboard for sale on our local auction site and I took a punt.

Did it work? No of course not as I've already exhausted my luck on that front but what the hell you brought it to hopefully get it going.

Initial test 8 hot RAM chips and no CLK on the Z80 and nothing on the 40007 which splits a 16MHz signal. And according to my logic probe nothing on the 74HCU04 which provides the 16MHz clock from a 16MHz Crystal.

I wound up replacing all of RAM chips as they failed in my chip tester and most of the 16MHz circuit except for the 74HCU04 which I didn't have a spare for and no joy so bit the bullet and got a vRetro replacement.

So now I get a 4MHz CLK on the Z80 but now the ROM chip got boiling hot so out with it and in with a socket and a 27128 which gives me this occasionally (other times no signal).

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So the next suspect is the MC6845 but I also ordered a TMP8255AP-5 chip as well just in case and have removed the chips and installed sockets for when they arrive which leaves me where I am currently at.

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[rubber_jonnie]

I don't really know the CPC464 very well, but I did wonder what power you're using for it? AFAIK it should be 5v in and is usually supplied by the monitor, and there is no regulation on board, it's all done at the PSU.

Since you've had so many hot IC's I thought it would be worth checking you don't have 9v going into it.

[Acsi]

Yep 5v but I suspect someone has maybe plugged in a 9v or 12v which would explain all fried chips.

[Acsi]

I found an Amstrad Diag rom and have tried that in the board and I get a consistent couple of screens.

This

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Followed by this where it will sit on with some of the pixels on the top line changing colour occasionally.

IMG_6700.jpeg (32.75 KiB) Viewed 82 times

Will need to wait for the couple of chips I've got coming to arrive for now.

[rubber_jonnie]

Yep 5v but I suspect someone has maybe plugged in a 9v or 12v which would explain all fried chips.

Worth a check, but sounds like you may be right in terms of it being over-volted.

[Dlfrsilver]

You did most of the job already. What remains are the roms (that's why they are hot, because they are shot!).

You need to burn new ones.... and remove the old ones, best is socketing them.

[Acsi]

Yep dead rom was removed and I have burnt a new one and a diag rom.

6845 arrived today and now the dial rom makes more progress showing 8 dead ram chips but they test ok so I'm thinking one or more of the logic chips that control the RAM.

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[Acsi]

Half way with the ram connected logic chips and the first 74HC153 I removed is faulty according to my chip tester, 3 more to go but they will need to wait.

[Acsi]

Four dead 74hc153's later (replaced with 74ls153s as that's all I could get local) and woohoo

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Now what to do with this board?

[PhilC]

That's great @Acsi