A3000 repair

[James1095]

So after not doing much Amiga related for a while, I found myself in possession of a nice looking Amiga 3000. Unfortunately the battery leaked and did some damage but I caught it before it got as bad as most of the pictures I've found online. Unfortunately it acts essentially dead. I've verified the power rails all look good and gotten as far as observing a roughly 1-second burst of activity on the buses and ROM enables when power is applied or I manually assert the _FAIL signal but then it goes dead. The clocks are still active but the address and data buses are static. I'm not real familiar with the Amiga architecture but my suspicion at this point is that it's starting to load the ROM and then crashing. Are there any common issues that can cause this? I was under the impression that the area around the battery is primarily video circuitry so I haven't yet desoldered any of the ICs in that area to inspect closely for hidden damage but it cleaned up pretty well and I don't see any rotted out traces. Does the Amiga have any sort of built in diagnostic like the POST codes on a PC? The machine was found in a hoarder house that was being cleaned out so I have no knowledge of it's previous status.

[kirk_m]

So after not doing much Amiga related for a while, I found myself in possession of a nice looking Amiga 3000. Unfortunately the battery leaked and did some damage but I caught it before it got as bad as most of the pictures I've found online. Unfortunately it acts essentially dead. I've verified the power rails all look good and gotten as far as observing a roughly 1-second burst of activity on the buses and ROM enables when power is applied or I manually assert the _FAIL signal but then it goes dead. The clocks are still active but the address and data buses are static. I'm not real familiar with the Amiga architecture but my suspicion at this point is that it's starting to load the ROM and then crashing. Are there any common issues that can cause this? I was under the impression that the area around the battery is primarily video circuitry so I haven't yet desoldered any of the ICs in that area to inspect closely for hidden damage but it cleaned up pretty well and I don't see any rotted out traces. Does the Amiga have any sort of built in diagnostic like the POST codes on a PC? The machine was found in a hoarder house that was being cleaned out so I have no knowledge of it's previous status.

http://www.skepticfiles.org/cowtext/comput~1/ami-init.htm

[Acill]

A3000 issues like this a really hard to nail down. Its one of the few machines I despise working on. I have been able to fix several, but with acid it can be deep issues in that area. I would start with pulling all the chips and making sure 100% of the traces to all sockets are good. You can find the schematics online here: http://www.amigawiki.de/doku.php?id=en%3Aservice%3Aschematics

[James1095]

Well that schematic is certainly a lot nicer than the one I was squinting at yesterday. Tonight I pulled the hex inverter at U477, it was pretty nasty but actually tested good out of circuit. I found an open trace between that and the phase pot on the back so I cleaned the area, installed a socket and repaired the trace. There was some corrosion in the socket for Denise so I replaced that too. The video circuitry seems a bit more lively now but the CPU is still not doing much. I removed the ZIP RAM that was installed and moved the extra chip RAM over into the fast RAM DIP sockets in attempt to eliminate RAM as a cause but that made no difference. Whatever is happening it's not getting very far, I can power cycle the machine or manually assert the _FAIL signal and it gives me less than a second of activity and then the CPU hard locks with no activity on any of the address or data lines, it's very consistent. I never get anything at all on the screen although I did get valid sync and a few random white bars at one point after I reset it. I think that's just a case of the lights are on but nobody's home. The video circuitry is running but with the CPU crashed there's nobody at the wheel.

[Acill]

Do you have a CPU board you can test with? Replacing the soldered on 030 is difficult but not impossible on the 3000. USe a hot air desoldering station if you attempt it and try using some of the chipquik stuff. It makes it very fast and easy, but its messy to remove that junk once done.

[matt3k]

I have seen a dead 030 throw yellow screens (just like if the daughter card was removed), don't know if that helps.  Acill is right, test with a cpu board to make sure.

I have seen lots of 3000s in my life, from my experience the PALS going bad and bad traces/vias are 99% of the failures I have seen.  Caps never go bad on the 3k.  I doubt it is the CPU.

The real nice thing about the 3000, if it is well maintained and never had a battery leak, and the PALS were replaced with GALS, the darn things never fail.  Make sure that you diligently clean the board, the acid leaks everywhere, so neutralize the entire board otherwise you may have future problems.

[James1095]

I don't have any other Amiga parts to try so that's not an option unless somebody wants to loan me a CPU board for testing. I am capable of surface mount rework but I'd really prefer to avoid it unless I'm quite certain the CPU is bad, especially since I can't just go out and buy a 68030. I hadn't thought of the PALs failing but if the code is available my device programmer does support at least some of those, what part(s) are appropriate for replacing them?

[Acill]

I think the code is available from Dave Haynie's site. I will look when home from work if you cant find it. I know he released the code for the 3640 boards.

[James1095]

I found a German site with the jdec files but it didn't say what GALs to use. I've worked with FPGAs and CPLDs but PALs and GALs are a bit before my time so I'm not all that familiar with them. Does anyone have a list of specific part numbers that are known to work?

I don't suppose there's anyone in the greater Seattle area with a CPU card we could try in this thing? I'd be happy to bring the machine by sometime to mess with it. I just have nothing to test the parts in and no spare parts to swap for diagnostic purposes. With what Amiga parts tend to cost, I don't want to just blindly throw money at it and hope something fixes the problem.

[matt3k]

Save yourself lots of time and pickup a set of GALS.  They are cheap.

http://www.amibay.com/showthread.php?65230-Amiga-3000-GALS-to-replace-PALS-For-Sale&highlight=GALS

Even if they don't fix the problem, they will run cooler once you fix the rig.

[James1095]

Cool, that thread has a list of part numbers that will work. I'll make sure my programmer supports them and then I'll buy some blank GALs, looks like they're still cheap.

[James1095]

So while I'm waiting for the new GALs to get here, I found the Amiga diag ROM which looks very promising. http://www.diagrom.com/

I found a place that has some 27C400-150 EPROMs, will those be fast enough to work in a 25MHz A3000 or do I really need the 105ns ones the author of the test ROM is using? Another potential option is to make an adapter for some 4Mb PLCC32 flash chips I have but I've got too many irons in the fire already.

[James1095]

Well I got the new GAL16V8D's and programmed them with the code I found for the A3000 PALs. Unfortunately it made no difference, although they do run quite a lot cooler than the old PALs did. Looks like I need to wait for the EPROMs to come so I can make some test ROMs. Hopefully that will provide some clues of what to check next.

[TjLaZer]

Did you fix it?  I see an A3000 for sale in the Seattle area on eBay now  

http://www.ebay.com/itm/Commodore-Amiga-3000-Working-With-New-Battery-/132010755276?hash=item1ebc7444cc%3Ag%3AxqcAAOSwA3dYM8UU&nma=true&si=jlGN0%252FWePa9fZt6sK%252F%252BPq7euEs0%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

[Acill]

Well I got the new GAL16V8D's and programmed them with the code I found for the A3000 PALs. Unfortunately, it made no difference, although they do run quite a lot cooler than the old PALs did. Looks like I need to wait for the EPROMs to come so I can make some test ROMs. Hopefully, that will provide some clues of what to check next.

That test ROM is John Hertell's work. He is a good friend of mine from Sweden. If you join the Commodore Amiga group on Facebook you can get in touch with him and get some direct support. The ROM works fantastic too, and he updates the code a lot, so plan to reflash that eprom several times, lol!!