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Old 15 November 2018, 15:36   #1
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Faulty A500 Rev 6a board, help needed.

I have an A500 rev 6a (1MB chip RAM upgraded) board that is driving me crazy.

The board boots to WB 1.3 OK, all the RAM appears present and it passes multiple, long Memory Doctor tests. Everything appears fine until I run specific demos or games.

For example, the State of the Art demo will run for a couple of seconds, but freeze just before the music starts. Armalyte will appear to load, but again freeze just before the music starts. The problem is the same every time - a complete freeze with the power LED flasing 5 times, no guru or error messages.

Wizball, Rainbow Islands, Parasol Stars and many others all run perfectly.

The thing is, if I press down on the board in the area highlighted in the picture, both SOTA demo and Armalyte will run OK, until I stop pressing, then the system freezes.

I have replaced the Agnus, CPU and ROM sockets and swapped out all the main chips with a known working set, but it made no difference at all.

Since flexing the board seems to fix the issue, I thought maybe a dry solder joint or even a crack in the board itself. I re-flowed everything that looked even remotely suspect and I have been over every mm of the board many times, but can't see anything obvious.

Any help appreciated.
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Last edited by Agrajag; 15 November 2018 at 19:58.
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Old 15 November 2018, 19:22   #2
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I had similar issues with occasional lockups and graphics glitches in some games and demos, and I also replaced my Agnus socket (which did have a crack) but to no avail.

I did notice however that one of the pins on the Agnus chip itself felt a little loose! So, I ordered a new Agnus on ebay and that completely solved my problems. Been running perfectly fine ever since. Maybe you're having the same problem?
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Old 15 November 2018, 19:54   #3
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I tried a replacement Agnus from a working system, but the problem remained.

I'm beginning to suspect that it may be audio related. When I get to the point at the beginning of the SOTA demo where there's a pause and no music, I stop pressing the board and the demo runs until the music starts again. Then it locks up. The Lockups aren't occasional. They occur at exactly the same point each time.

I'm not sure how the audio could lock up the system, except for a bad Paula maybe, but I have tried 3 different Paula chips and it's exactly same, so it can't be that.

I'll experiment some more.

Last edited by Agrajag; 15 November 2018 at 20:08.
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Old 16 November 2018, 02:36   #4
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All custom chip DMA (including audio) is routed through Agnus, so you can't just write it off like that.

Visually inspect the Agnus socket under magnification, including the pins on the bottom where they are soldered to the motherboard. Measure resistance from each pin to another location on the board.
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Old 16 November 2018, 16:34   #5
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I would simply replace the Agnus socket at this point. It is the most likely cause.

EDIT: Oh you already did that... Is this issue exactly reproducible every time at the exact same place in the two titles? You might have to buzz every track.

Last edited by kaffer; 16 November 2018 at 16:39.
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Old 16 November 2018, 19:38   #6
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I spent a few hours probing the Agnus socket to various points around the board and I couldn't find anything wrong.

This board is far more trouble than its worth, so I think it will end up as a parts board.
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