Weird issues with A4000

[shovel]

I have a 4000/040 desktop that (apart from some minor configuration issues when first I got it) have been working just fine for many years.
At some point this week, something happened.

It started with workbench drawer windows freezing, and then freezing the OS completely. The system could be restarted by keyboard, but everything froze again when I opened any disk/partition window.

I was thinking that maybe there was something loose inside, IDE-connector, CF-card or such. So I opened the case and checked everything. I reseated a few connectors but couldn't really find anything distinctive.

I started the system again and could actually open disks, drawers and files. But suddenly the monitor went black.

Fast forward an hour and I came to the conclusion that the VGA output no longer works, and the audio output level is very low and heavily distorted. I can get video from the large video connector, connected to a TV via SCART, but the image is distorted with lots of horizontal lines. See photo.

I have tried taking every expansion card out (VGA, NIC and SCSI), but it makes no difference. I'm no expert on Amiga hardware and I'm clueless right now.

What happened here and are there anything I can do about it?

[Boing-ball]

You haven’t mentioned this but has the following been performed in the mainboard:

1).. Original Varta Barrel battery been removed?

2).. Have the Capacitors been replaced with new ones?

From what you are describing, makes me think you have failing Capacitors or a Leaking Varta Battery causing havoc.

[shovel]

The battery was removed when I first got it, probably about 10 years ago. The remaining mess from the battery was later neutralized/cleaned up in 2015.

The capacitors were replaced in 2015, on both the main and CPU board. The CPU board also had some of them reversed, if I recall correctly. I think there were some CIA chips that got replaced too.


I still have the original PSU in original condition. I just measured the voltages at the PSU connector and they seem ok, with 12v being a little low at 11.9.

[Boing-ball]

Capacitors replaced with good makes? I.e Japanese ones like, Panasonic etc..?

[shovel]

I can't determine what the SMD caps are but the thru-hole ones says nichicon.

The guy who did it wrote:

I use professional tools and supplies, and brand capacitors (Panasonic, Nippon Chemicon, Rubycon etc.).

[Boing-ball]

Yep. Nichicons are a good make.

The only thing is if the corrosion is still present under the board layers and has started to spread causing connection problems.

Failing that, check for any loose chips in there sockets.

There maybe also an issue with board bend. Where the board is not sitting correctly in the case and causing connection issues.

[Castellen]

Hard to say without a few measurements, but the clues suggest it might be an open circuit line in the register data or address bus.  Use a scope to check for normal looking activity on all lines of DRD and RGA at U400 and U450, usually not too hard to spot.

If there has previously been a lot of battery corrosion, this can damage the vias around the left hand side of the SIMM sockets, and some of those are part of the data/address bus that might explain your symptoms.  I doubt you'll visually be able to see anything useful, it'll need measurements to see exactly what's going on, after which it's easy enough to locate and repair an open circuit via for example.

Not sure if this is one of the boards I've worked on previously or not, but either way, feel free to contact me for repair options if you can't figure it out.

http://amiga.serveftp.net

[Tumbleweed]

This will help you check traces etc:

https://www.amigapcb.org/index.php

I used it extensively to fix my A4000D battery damage. Board had battery removed years ago and had been repaired - RTC and audio (leaky caps). Turned out I had broken traces and a problematic Buster. I got a set of Diag Roms and spent hrs with my multi meter checking traces; resistance; voltage and capacitance until I narrowed it down.

Alternatively you can get someone to repair the board for you. Castellen fixed my 3000T a few years ago and its been working great ever since. 

Weed.

[shovel]

Thanks for the information, I'll have a look at what was suggested above but I don't think I will be able to do any repairs myself.

The bottom case may have been slightly warped, a workshop had it some time ago to make some modifications and they weren't very careful. I will loosen all the screws and see if it makes any difference.

Not sure if this is one of the boards I've worked on previously or not, but either way, feel free to contact me for repair options if you can't figure it out.

http://amiga.serveftp.net

It was a guy in Denmark that did the previous work.
Where are you located?

[shovel]

Well, still not sure what is going on. I loosened all screws holding the mainboard and made sure there was no tension in it.
Then I turned on the power and everything seemed normal again, including audio?

I will try to reassemble everything in steps, including all the zorro cards and see at which point the problem comes back, if it does. Like several people mentioned earlier, sounds like it could be some internal connection problem?

Also, what is usually recommended: keeping the original PSU and replace the capacitors or swapping it out for something newer (SFX/ATX?)

[Castellen]

It was a guy in Denmark that did the previous work.
Where are you located?

I'm based in New Zealand.  The guy in Denmark (Jozsef) sends me his complex jobs for repair, though he's great with capacitor replacements, etc.


From your latest description, there's probably either a solder joint, PCB track or via that is cracked, causing the intermittent problem.  You might be lucky in that if you keep the main board in that position then it might be OK, or perhaps the fault will show up again.  These intermittent problems can often be unpredictable and difficult to track down.


Regarding the power supply, I'd recommend keeping the original one.  The design is fairly reliable, fit for purpose, and it's easy to replace the capacitors as needed.  Plus you don't need to mess about with modifying anything.

[Boing-ball]

Well, still not sure what is going on. I loosened all screws holding the mainboard and made sure there was no tension in it.
Then I turned on the power and everything seemed normal again, including audio?

I will try to reassemble everything in steps, including all the zorro cards and see at which point the problem comes back, if it does. Like several people mentioned earlier, sounds like it could be some internal connection problem?

Also, what is usually recommended: keeping the original PSU and replace the capacitors or swapping it out for something newer (SFX/ATX?)

Sounds like Board bend and there maybe micro fractures or dry solder joints.I don’t think a PSU is going to sort this….

You can either get the board accessed for the issue. Or go one further and have the chips etc.. Transplanted onto a re-Amiga ACILL 4000 Motherboard.

[mechy]

Reseat the kickstart Roms and the accelerator.  hopefully its just a bad connection. Inspect the PSU connector and plug pins for bad contact.