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Old 24 June 2019, 00:11   #1
Vypr
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Dead A25000 memory card

I've finally managed to coax a dead A2000 back to life. It was initially sold to me as not working with a green screen at boot.

After replacing the PSUinternals with an old ATX PSU, replacing all the memory chips and after several weeks of headscratching getting the right mouse button to work (turned out to be a tiny bit of corrosion near the battery was causing that problem) The system is finally working solidly I am now turning to the two boards that came with it.

The first is a Golem SCSI card with an old MFM drive. I'm not even going to bother with that, the drive is most likely unsalvageable and it's highly unlikely I'll find a replacement drive of this type so I've replaced ti with an A2091 with a SCSI2SD card.

The other card is an old A25000 2Mb card which is non functional.
At the moment it is not being detected at all. On bootup the system Gurus immediately but will then boot into Workbench but the card is not present.
When running DiagROM, the autoconfig goes into a loop, constantly detecting the card and allocating memory space to it before giving up.
I put a scope on the data lines of all the memory chips and there is activity on them.

I don't have high hopes for this card as I think that the onboard memory chips were fried when the PSU went bad and it's likely it has fried this card too but I'd like to at least make the attempt to find out what has gone wrong.

Has anyone here had any experience with these cards?

Last edited by Vypr; 24 June 2019 at 00:12. Reason: spelling
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Old 05 July 2019, 15:25   #2
cpiac64
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test it whit anither diagnostic like Logica's Dialoga
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Old 05 July 2019, 21:18   #3
TjLaZer
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Dead A25000 memory card

Where to find this other Diag ROM?
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Old 11 July 2019, 01:15   #4
Vypr
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Well, I've recapped it, replaced all the memory chips and now it's not being detected at all. DiagROM no longer finds any card.
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Old 20 July 2019, 22:01   #5
Vypr
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After several weeks I now have it running proeprly. Since there isn't much info on troubleshooting this card, I am puttong my findings below in case it helps someone else.

Note: The A25000 and the A2052 are pretty much the same card, what works for me will work for this, it may also apply to the A2058 card which although using 1Mx1 chips for a full 8Mb, the board layout is identical.

I've attatched an image of the board showing how the memory chips are laid out. There are 4 banks of 16 chips, each chip stores 1 bit. The first 8 bits are on the left side of the board, the last 8 on the right. I have coloured each chip to show which bank it belongs to.

Red = Bank 1
Yellow = Bank 2
Blue = Bank 3
Purple = Bank 4

Each bank is 512Kb (2Mb on the A2058).

There are two jumpers on the board marked J1&J2, on the A2052 I could not find documentation on what they did anywhere but withe a bit of trial and error I found they enabled and disabled memory banks. The setting s are as follows:

J1 J2
On On - Bank1 enabled only - 512Kb
On Off - Bank1 and Bank 2 Enabled - 1Mb
Off On - God knows, when I tried it it decided there was 4Mb available
Off Off - All banks enabled - 2Mb

If you have memory problems and suspect faulty chips, you will need to desolder all 64 chips and I reccommend putting 16 pin DIL sockets in to make swapping chips around easier. Be careful of the decoupling capacitors between every row, they are easy to damage and can fall out if you are using hot air to desolder. To replace them you will need .33 uF ceramic capacitors with a pitch space of 5mm.

Check with a multimeter for continuity. Note that if there is a short on any of the address lines then the Amiga will not detect the board or anything downstream of it so be careful. You can find the schematic here: http://www.retro-commodore.eu/amiga-tech.

Once you have the sockets in place and checked for continuity set the jumpers to 512Kb and place chips in Bank 1.
Note that if there is a bad chip in bank 1 bit 1, Kickstart will report the board as defective.

I recommend using Amiga Test Kit (Formerly known as SysTest) to test the RAM as it will test each chip and indicate which one in the abnk it found defective.
Now it's just trial and error, swapping chips around till you have identified the defective ones

In the case of my board there were two broken traces and 14 defective memory chips
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