A2000 help please

[stephen_usher]

Well, it seems to be executing code anyway. Whether it's correct code we don't know, but it's very likely that the DiagROM is running but getting stuck when trying to set up the serial port. You have put a terminal in ther serial port haven't you?

It could be that it's got far enough now to output some diagnostic information as you've fixed the chip select line on the CIA.

[Steve_w]

Well, it seems to be executing code anyway. Whether it's correct code we don't know, but it's very likely that the DiagROM is running but getting stuck when trying to set up the serial port. You have put a terminal in ther serial port haven't you?

It could be that it's got far enough now to output some diagnostic information as you've fixed the chip select line on the CIA.

That's exactly what I thought, connected the serial port to my laptop, still no luck with output.

[Steve_w]

Well I'm getting somewhere now, after speaking to guy I am repairing it for again, I thought the custom chips were all know good chips, turns out he has not tested them, they came with the board.

I tested them in a working A500 rev board, one CIA is faulty (green screen) and the Agnus chip had dirty pins which initially after installation in the A500 rev 5 produced the same error I am seeing with the A2000, a black screen. After cleaning the pins and retesting in the A500 the A500 booted to KS screen, so not a dead Agnus, just a dirty one.

I put all the chips back into the A2000 minus the faulty CIA (U301 is empty at the moment) and it booted Diagrom !!! :D :D :D

So now to figure out from this what DRAM or one of the many logic chips may be faulty. It seems D0-D6 are stuck, almost a complete logic chip.

RAM error.jpg

[stephen_usher]

Probably one of the transceivers... or could be the control signals for the outputs given that it's all ones and the outputs are tristated, meaning that if the output isn't enabled the bus will be pulled high... Hmm... There are only pull-ups on the memory side on the Amiga I think, so that would suggest the CPU -> RAM direction.

[Steve_w]

Yes okay, D0-5 are pulled high, but D6 is pulled low, so either U105, U106? I've already replaced u603 on the bus side. U603 and U604 also have pull up resistors was well.

Is there a way to determine which one, U105,U106?

[stephen_usher]

I would suggest desoldering, socketing and then testing the chips in a tester. If they pass then you know that they aren't the problem and you can just put them back on the board.

[Steve_w]

I would suggest desoldering, socketing and then testing the chips in a tester. If they pass then you know that they aren't the problem and you can just put them back on the board.

When I got home today I tried piggy backing the chips, that worked !!! :D

piggy back.jpg

Now I have an address error, its like I'm inching towards the finish line here :lol:

address_error.jpg

[stephen_usher]

If you're still piggy-backed then it could just be an address pin not correctly connected. I'd desolder the original RAM, fit sockets and put the chips in there... maybe test the originals too in a tester just in case.

[Steve_w]

If you're still piggy-backed then it could just be an address pin not correctly connected. I'd desolder the original RAM, fit sockets and put the chips in there... maybe test the originals too in a tester just in case.

Yes I'll do that next, although when probing the address pins A9,11,12 on the CPU, they are pulled low the others have activity.

[stephen_usher]

Check U601, that 74LS245 is bidirectional and if faulty could pull those lines down potentially.