A3640 problem & A4000 questions

[Olecranon]

Hi Everyone,

I just purchased my first A4000 system and it looks like it's going to be a nice machine.  The system currently has an A3630 CPU card installed.  The person I purchased it from gave me an A3640 board and a couple extra A3630 boards that he said he couldn't get to work.  I was able to get the two A3630 boards running, but not the A3640 board.

Does anyone have any suggestion?  I set the jumpers on the A4000D motherboard from INT to EXT for the clock, but that made no difference.  I believe all the jumpers on the A3640 are closed and its set to maprom enable.  Oh, it's a version 3.1 of the card.

A couple other questions.

System has 3.0 in ROM.  Can I run WB3.1, WB3.5, or WB3.9 with KS3.0 or do I need to upgrade to the 3.1 ROM?

Thanks for any suggestions.

[A4000_Mad]

You can install and use WB3.1 with 3.0 ROMS but you will need 3.1 ROMS for OS3.5 and OS3.9. Hmmm....Not sure about your A3640 as you have tried the jumpers in both INT and EXT.

A4000 Mad

[Bazzaq]

Did you change both sets of jumpers>

CLK 90 Clock Source J100 1-2 Internal (020/030)
                         2-3 External (040)
CPU Clock Source J104 1-2 Internal
                      2-3 External

I can't recall what mine is set to but it was basically the opposite of the 030 setup.

[AMC258]

Depending on this board's history, it could be fried.  I have come across several fried A3640's that were used in A3000s without any cooling modifications.  The 68040 runs really hot, almost as hot as an Intel chip.

[Jeff]

Some A3640's also had some caps installed backwards at the factory. I have at least one rev 3.1 like that. Sometimes replacing the small surface mount capacitors can bring them back to life.

Good Luck,
Jeff

[Olecranon]

After some examination of the board, I'm starting to wonder if 3 out of the 5 capacitors are shot.  I used to be a PC Computer tech and saw lots of boards with bad capacitors.  Usually the caps would be bulging with electrolyte leaking from the top.  These dont look like that, but the metal contacts look corroded.  Two of the five look fine.

I let the A4000 sit a black screen for awhile and the 040 chip never increased in temperature.

Has anyone done a capacitor swap on one of these cards?

I found some good info here, but it would be nice to talk to someone who has done it.

http://joj.home.texas.net/amiga/amiga00.html

[Olecranon]

Jeff wrote:
Some A3640's also had some caps installed backwards at the factory. I have at least one rev 3.1 like that. Sometimes replacing the small surface mount capacitors can bring them back to life.

Good Luck,
Jeff

Ok, looks like we might be on to something here.  The instructions I have state that I need 22uF 16V leaded radial capacitors.  Anyone know if I can pick something like that up at radio shack  :-)

I might go ahead and give it a shot.  My soldering skills are above average, hehe

[amiga92570]

https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=193009&pa=193009PS

[AMC258]

Radio Schack will have the condensers.  Keep in mind that the voltage rating has to be at least 16V, not exactly 16V.  So, if you get a 30V one, that's OK.

[Jeff]

Look very carefully at the polarity, some are MOST LIKELY in backwards from the factory. These are probably the ones that are corroded at the bottom and have failed.

They are surface mount and the pads on the A3640 lift very easily so you have to be careful. Perhaps practice on a junk board with similar parts and get comfortable if you haven't done this style before.

Good Luck,
Jeff

[Matt_H]

3 of the 5 capacitors on the 3640 have the polarity reversed because the silkscreening on the PCB is wrong - those are probably your bad ones.

I started a thread on this last month - there might be some good details and links in there as well.

I didn't trust my soldering skills, so I had Amiga Center correct it for me. Still waiting on the postal service to deliver the thing, though!

[Olecranon]

Matt_H wrote:
3 of the 5 capacitors on the 3640 have the polarity reversed because the silkscreening on the PCB is wrong - those are probably your bad ones.

I started a thread on this last month - there might be some good details and links in there as well.

I didn't trust my soldering skills, so I had Amiga Center correct it for me. Still waiting on the postal service to deliver the thing, though!

How much did the repair cost you Matt?

[Olecranon]

amiga92570 wrote:
https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=193009&pa=193009PS

Thanks for that link.  I'm not really should how I would solder that.  I haven't worked with surface mount caps before.  I'm thinking I might just get a few trusty ole radial style ones and bend/cut the leads.  

[Zac67]

Resoldering new caps is rather easy, but removing them can be hard (to the pads). I clipped the upper part of the caps, removed the plastic base and then desoldered the rest - killed two pads that way, which I had to repair afterwards.

Reportedly the easiest way is to use two soldering irons to desolder both sides simultaneously.

ALL but the very last A3640s had reversed caps. After the design was finished, they were added just before production began - and C= didn't notice until years later...

[Olecranon]

I received a quote from Amiga Center that repairs would not exceed 70E (about $91 USD), but I can send it in for a free diagnostic.  I would guess that capacitor replacement would be fairly cheap?  

Then I probably need to add shipping to/from France on top of that (not sure how much that is).  I only paid $150 for computer, so I hate to spend another $150 just to get the 040 up and running.  I'm also a little concerned about trying to purchase another one of these with the problem being so widespread.

Any suggestion?  I've never dealt with Amiga Center before.  Should I attempt the repair myself, then send it in if I fail?