A4000 troubleshooting

[alenppc]

I have an A4000 motherboard that died after being in use for an extensive period of time (was on for about 7 days straight).

Premise:
- The board is completely recapped.
- No battery corrosion, no dead traces.
- Does not have the RTC diode fitted (never did).

Symptoms:
- At powerup the screen flashes alternating between green & grey.

I have tested all the obvious: chip ram reseating, chip ram socket resoldered, boot with/without various configurations of RAM/different simms plugged in, different CPU cards, different power supplies, different ROMs. The symptoms are always the same: green/grey alternating screen colours.

It is possible that a component died because of the heat buildup inside the case, but which one?

Currently, no components get particularly warm to the touch on the motherboard.

Any ideas?

[hese]

Originally Posted by alenppc

It is possible that a component died because of the heat buildup inside the case, but which one?

Alice, Bridgette and CIA can cause such problems.

[bebek]

And you have tried different CHIP memory ?

[alenppc]

@bebek yes, I have.

@hese I can try different CIAs but I have no spare bridgette or alice :| I will keep that in mind though.

[Loedown]

Warm the whole motherboard using a hair dryer and see if it boots with a ctrl-A-A

If it boots then you have a hot and cold fault, use freezer spray and the hair dryer to isolate the issue.

[alenppc]

OK, I made some progress. Found a broken via near the IDE chips that was causing the green screen at boot. Once patched, the board now displays green with no chip ram and grey with chip ram. Still no boot though, permanent grey screen. I looked for other broken vias/traces but did not find any. Will try the what Loedown suggested tonight.

2nd: I am also attempting to revive another board. It has really extensive leaked battery damage. After stripping and cleaning the affected area, I believe I have found most of the corroded traces and patched them with jumper wires. I replaced the SIMM sockets also, cleaned contacts underneath and patched corroded traces. I replaced U177 and U976, but the board does not boot: black screen. No green screen displayed with no chip ram. Can U177/U976/U975 be responsible for this?

[hese]

Faulty U975/U976 can be responsible for the computer not to boot.

[alenppc]

A small update that may help those encountering a similar problem; For the 2nd board mentioned above I replaced U177/U975/U976. Fortunately these parts are still manufactured and easy to find. A faulty U975 caused the screen not to produce proper sync. After replacing them I could see a clear dark grey picture, but still no boot. It also turned out the CPU slot pins needed to be reflown with solder. After doing so, the board now works.

Still no news on board #1. Permanent grey screen. Warming it up with a hairdryer made no difference. Tried changing CIA U350. No difference, will try reflowing the CPU slot pins like I did with #2.

[voyager_1701e]

Hi
Although this may have nothing to do with your problem I am currently restoring 2 a4000s. Both the boards had extensive acid leakage from the batteries and also electrolyte leakage from the caps.

Whilst you problem may be an active component simply expired its life....my experience suggests carefully examine all the areas close to all the caps and battery with a good strong light and good magnifying glass.

I am lucky I've had no eaten tracks that I've found so far. However by simple close examination I've found a couple of passives literally snapped in 2 but not visible to the naked eye. Also the condition of the solder joints on all components around these areas will give clues to whether there are or maybe issues.

I'm going to follow your thread with intetest!

Good luck

Ash

[alenppc]

On board #1 I found and replaced 2 ceramic caps that had blown up on the underside of the board, one close to the broken via. I suspect all this damage was caused by a faulty PSU.

In fact, after taking the PSU out of the case and testing it on its own, it was producing very unstable voltage. Shortly after, one of the capacitors inside the PSU exploded as well. I threw it away and replaced it with a new PSU. I wish I had done so earlier to avoid damaging the motherboard. For the time being it remains in its comatose state... I am not sure what else to try now.

For the #2, I found about 8 corroded traces, and other than the battery area damage and the CPU slot connector, it had no other damage.

[Loedown]

Originally Posted by alenppc

On board #1 I found and replaced 2 ceramic caps that had blown up on the underside of the board, one close to the broken via. I suspect all this damage was caused by a faulty PSU.

In fact, after taking the PSU out of the case and testing it on its own, it was producing very unstable voltage. Shortly after, one of the capacitors inside the PSU exploded as well. I threw it away and replaced it with a new PSU. I wish I had done so earlier to avoid damaging the motherboard. For the time being it remains in its comatose state... I am not sure what else to try now.

For the #2, I found about 8 corroded traces, and other than the battery area damage and the CPU slot connector, it had no other damage.

Ah yes, exactly why I use ATX supply for my A2000. I hope you can fix the board but I would suggest it may need many chips replaced.

[alenppc]

Another Amiga 4000 saved...

So, I still haven't had a chance to look at 4000 #1, but somebody asked me to look at another board (will call it #3).

It took a while, but I think I isolated everything. This one suffered badly from microfractures in the solder joints. Alternating dark blue/grey screen at boot and constant reset signal on/off, turned out that refluxing and resoldering Ramsey pins cured this problem.

I did the same for Alice, to cure graphics corruption on the screen after the machine was on for a few minutes.

Broken traces on the upper side of the board immediately adjacent to the CPU connector can also cause a green screen issue.