Repair Log – Amiga 1200

In a tantalizing tale of solder, accelerator cards and ham fisted muppets, Womble takes us step-by-step through the analysis and repair of what was supposed to be a very unhealthy Commodore Amiga 1200HD.

A bit of a break from Arcadia but much the same kind of work involved…

My regular search for interesting faulty stuff on eBay threw up a gem last week, a faulty Amiga 1200/HD-40 unit. The seller had photos of it connected to a Commodore 1084 monitor via the video port and reported that it just gave a completely blank screen. Another photo in the set was of the back with the trapdoor open showing the underside of an unknown expansion board.

Going by the eBay photo and by trawling through all the A1200 expansion card photos on www.bigbookofamigahardware.com I was pretty sure that the card was a GVP A1230 Jaws-II accelerator as the pattern of SMD components and the general layout was correct for what would be visible through the open trap door. A very decent card and worth a fair bit on its own.

Had they actually specified what the expansion board was it would have gone for a lot more, but the hammer came down at a bargain price for a minty looking A1200, with a PSU, mouse and manual, even without the accelerator card.

So I ended up with a stone dead A1200 on the repair bench, with a partially identified accelerator card.

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If I was right then the card should have two SIMM slots on the other side, but GVP used proprietary SIMMs on their cards which are ridiculously expensive to get hold of these days so I was hoping the slots were populated with something.

As the seller had already tested it with the right monitor (even owning one suggests he knows enough about the Amiga range to not make stupid mistakes when testing gear) I decided to strip it down for inspection before powering it up again. I also did not want to try to get the accelerator card out without seeing what was going on from the other side as it is a ridiculously tight fit.

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WTF? – a 130MB 3.5″ HDD bodged inside instead of the correct 2.5″ HDD on an official caddy? It was held in place by two strips of bent metal and was resting on the motherboard on a bit of roughly cut plastic sheeting. The PC style molex connector power leads were bodged onto the inside of the power connector. All in all pretty nasty.

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First glance of the accelerator card confirmed the score!

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It is a GVP 1230 Jaws II card with a pair of 4MB GVP SIMMs, which seem to go for $50 each on eBay, and thankfully it was free from battery leaks.

So, to get a baseline test it was stripped back to a bare bones A1200 to rule out hard drive faults and accelerator card issues.

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Sadly it was still dead, no signs of life on the screen, even the noise from the HDD when it was still installed was just the standard HDD spin up and head noises, no signs it was being used by the system.

On closer inspection of the PCB it was clear I was on the trail of a hamfisted muppet, for reasons unknown someone had been in here beforehand, and decided that a lot of the solder joints would benefit from the application of their soldering skills, and here I am using the word “skill” quite wrongly.

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In this manner they have converted dozens, if not hundreds of perfect factory joints into blobby, crystalline, ugly and potentialy bad joints. There seems no specific logic to what they were doing, as if they tried a few here, a few there, probably with optimistic power up attempts in between.

There was also signs that someone less clumsy had been here too, a slight scratch on the board had been investigated by scraping off the lacquer either side to check continuity across the scratch.

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This is actually neatly done, but the area should be treated with new lacquer to seal it again, I assume they gave up on it at this point.

So I checked the voltage levels first then went back to the board inspection and quickly found the prime candidate for the fault.

Among the chips the had been touching up were the surface mount 74LS245s at U45 and U47, there are four of these in a column on the board and he had decided to improve the soldering on one and a half of them, not sure why only one chip and half the pins on another.

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What he had actually done was to completely hose the soldering on U47.

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Pin 13, i.e. the third pin in from the left is missing all the solder, this is what happens if you touch up old solder joints without using flux, the solder gets sticky and clingy and you end up dragging it away from the joint on the iron. Pin 12 isn’t much better but it is still attached, pin 13 is just resting on the pad, which may work for a while until oxide built up at the touch point.

As soon as I applied the slightest pressure to this pin the system booted to the “insert disk” screen.

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So the joint and all others on the two messy 74LS245 chips were tidied up to complete the fix.

With the hard drive reattached it booted into workbench happily.

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On plugging in the accelerator card I was greeted with a blank screen, this was remedied by reseating everything on the card, the 68030 CPU, the clock crystal and both SIMMS.

A complete removal from the card and re-insertion scrapes away the 20 year old oxide layers restoring the contacts. With that reinstalled the system booted in about half the time.

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The PCB needs some rework, to tidy up the nasty soldering on a lot of the components, it also needs to be cleaned around the worked on areas as there is a lot of flux residue from areas that were resoldered rather than just reheated dry. some of the capacitors are probably a bit past their best, but only one shows sign of a slight leak which shows up as a slight furring of nearby solder joints.

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Future plans include, the bodgy workmanship clean up, obtaining a 68882 PGA Co-Processor chip for the expansion board (I could potentially replace the 40Mhz 68030 with a 50Mhz one on this card but I probably wont bother). I will also fit a CF flash card in place of the HDD, I actually do have a 2.5″ drive on an official A1200 HDD caddy for some unknown reason so will fit the CF card on that.

Heres the official caddy and drive from a 1200 and the one they had crammed in.

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Both my 2.5″ HDD and the 3.5HDD are pretty loud, the current draw from the 3.5″ drive causes some image instability when it is accessing data, which is a design flaw on the board that I could rectify, but with a CF card the current draw will be minimal so the problem will likely vanish anyway.

Anyway – a quick reassemble and time for a full test…

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…with the title of choice for all my 8 and 16 bit repairs when possible…

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…Treasure Island Dizzy!!

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All in all a damn fine eBay score!! I suspect the bad contacts on the expansion card resulted in a flaky Amiga, which led to the internal investigation and the random solder touch ups, which upgraded it from a flaky Amiga to a dead one. Its never a good idea to do this to anything electronic, your chance of finding a bad joint if you can’t see it by eye are slim and your chances of introducing new ones is very high.