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Old 14 January 2017, 17:07   #1
Vypr
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A1200 boot issues

I just recently bought, in auction, an A1200 fairly cheaply (Around £70). System was in good physical condition but unfortunately will not boot, I suspect it is a caps problem but was hoping for a 2nd opinion.
Symptoms are as follows:

When booting , it usually goes to a black screen, however on occasion I will get:
a Solid Yellow screen
A solid red screen.
Standard white, black, grey then corrupted graphics.

I have tested the Kickstart ROMs in a working system and they are fine, I tested working Kickstart ROMs in this system and get the same problem.

I also plugged in Working M-tech 1230/28 accelerator and again, got the same symptoms.

Pic of board below:


Any ideas?
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Old 14 January 2017, 17:13   #2
Pat the Cat
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Hmmm... I would change the 3 tall capacitors around the power supply input. One of em looks bulged to me.

It's probably not the only fault, but it might be - wobbly power input gives wobbly running conditions (different faults reported, etc).

Also, check for odd bits of metal causing shorts, bad connections, similar.
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Old 15 January 2017, 15:20   #3
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It's normally the small SMT capacitors that fail rather than the tall ones, and provided your PSU is good, the machine should run fine without them anyway. I would look carefully for any leakage around the small aluminium SMT capacitors - it's the leakage from them that will corrode tracks and cause problems. It's hard to tell from the photo whether that might be the case or not.
It's worth ruling out the PSU as well if you have another one handy, as Pat said, funny power causes strange things to happen. My gut feeling is for a bad solder joint on one of the major chips that's upsetting the bus.

East Kilbride eh? I'm in the southside of Glasgow so if you wanted me to give you a hand with it, feel free to drop in
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Old 15 January 2017, 16:50   #4
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I have tried another PSU with the same results. I have a 1200 brick and an ATX to Amiga convertor box so the power input should be fine.
Daedalus, if you PM me your address, I'd be happy to arrange a time to drop it in. If you do recapping services, I have another two (possibly 3 if I can dig it up) A1200 boards that could do with some attention.
I'd give ti a go myself but my hands are a bit too shaky to attempt this kind of fine soldering work.
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Old 19 January 2017, 11:00   #5
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Well, thanks to Daedalus for taking the time to look at the board, I think the problem is with Alice. I found that if I put pressure on Alice, specifically at the bottom right of the chip, I can change the boot symptoms from straight black to light grey followed by a random error colour, most commonly yellow but sometimes blue, green and occasionally red screens.
Also, Alice can become very warm to the touch at boot, not burning hot but noticeably warmer than the other chips.
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Old 19 January 2017, 12:19   #6
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Oh dear Alice does get quite warm so I don't know if that alone points at a fault, but given that the behaviour changes like that, it does indeed sound like a fault with Alice.
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