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Old 18 April 2009, 23:49   #1
r.cade
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Amiga 3000 Resurrection

Hi guys,

I found an old A3000 at a thrift store a year or two back and it seemed to work fine. Left it transferring some data over night and woke up to a stone dead old friend.

Further testing showed it was shorted somewhere on the board- the power supply would come on with drives on it, but immediately shut off when plugged into the board. I replaced all the caps and removed all the chips on the board one by one to try to find the fault to no avail. I put it on the shelf in digust.

Fast forward a couple years and I got sick of seeing it there dead on the shelf. I ordered a new ATX power supply converter from nathan @ amigamaniac.com and covered my eyes and powered up. Immediately, C870 and C872 near the ZIP sockets got red hot, smoked, and blew up into tiny bits. I powered off, clipped the remains of them clean, cleaned off the burned section of the board and it now powers up with nothing else exploding.

Any idea what would cause that? There were no chips in the ZIP sockets and I don't see any short circuits near there...

I'll see about replacing those and see if new ones blow also.
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Old 19 April 2009, 00:50   #2
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Those old electrolytic capacitors are evil! They can be the culprits for the Amiga not working.
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Old 19 April 2009, 17:30   #3
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Yeah, but these are MLC (multi-layer ceramic). I've never really seen them go short before...
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Old 19 April 2009, 23:08   #4
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Apparently not so rare. Yet another thing to look for on these old computers.

http://www.calce.umd.edu/whats_new/2001/Ceramic.pdf

Unfortunately there are probably 100 of these on an A3000 board. They are used to decouple every single chip on the board.

I guess this board could have been in a very hot or very cold environment for over 12 years. When I found it, it hadn't been used in that long according to the file dates on the hard disk (which still boots).
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Old 20 April 2009, 00:44   #5
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Thanks for the link R.Cade! I read electronics in school, and a bit in my further education, and there they mostly pick up on the failures that Electrolytics are subjected to. So the cheramics blow up as well, eh? Very interesting.
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Old 20 April 2009, 04:28   #6
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Quote:
Originally Posted by r.cade View Post
Yeah, but these are MLC (multi-layer ceramic). I've never really seen them go short before...
They go short due to stress, they crack and very easily internally, creating the short. I worked for < insert large electronic manufacturing corporation here > in their production area and on a board for < insert car manufacturer here > they had a string of about 50 capacitors close to the edge and with the gentle technique of jamming the finished board into their shells, they wondered why we got returns for shorted parts.

Paul
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Old 20 April 2009, 22:56   #7
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Paul: LOOOL!!

Haha, well, it's a complete mystery, now isn't it?
Seriously tho... I would suppose that the cure for some of the "manufacturing-problems" were eventually, hrrrm, corrected?
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Old 21 April 2009, 02:18   #8
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I disassembled and reassembled it to clean it the night I bought it. I wonder if I bumped those caps with the frame. The way the A3000 internals fit together is sort of unruly.

Anyway, parts are on the way to replace them and find out. I also tore out most of the floppy controller logic as well looking for the short a year back, so I need to replace some of the TTL logic there. Nobody really sells the DM74LS chips that are on the board, only the SN74LS types. Hopefully that'll be OK.

Last edited by r.cade; 21 April 2009 at 02:25.
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Old 22 April 2009, 05:28   #9
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Those "SN" parts are OK!

You really will not mind who made the part! All you need is the part is the same type.

But if you want better parts, look for "54LSxxx" instead of "74LSxxx" ones. 54 prefix means military grade of TTL chips, they have more voltage-tolerance and are better "abused" without frying themselves.
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Old 24 April 2009, 02:09   #10
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It lives. Replaced caps and they didn't blow again or do anything strange. Rebuilt the floppy controller logic and it works fine also. I'll leave it on all night again and see if it croaks.

At least I know the A3000 PSU will cut off when any problem occurs.
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Old 24 June 2009, 15:34   #11
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This machine is still running strong except for an odd video problem (that existed before the cap shorting).

There are odd lines on the bottom of the screen when the built-in flicker-fixer is used, but only in high-res laced modes.
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Old 24 June 2009, 16:20   #12
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this truely is a great recovery drama.... better than watchin' the TV!!!!

awesome stuff m8.... next time though.... PICTURES!!!!!!

*ahem.... some hardware pr0n pics please
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