Duo full cap job - from fail to 'no way....' and finally hooray!

[Game-Tech.US]

Ok, I did a full cap replacement job for a guy with cd audio problems.
When I got it he had already started and the cd was unplugged from the mobo so I didn't test it at all, but HU worked fine. So I said screw it and went ahead and replaced all the caps. Then I went to test it before I put it all back together, HU still worked fine, but without a HU it wouldn't boot to the bios screen, it would give me the solid color screen like a dirty hu or whatever. PISSED!
I spent a whole evening looking at old threads of other ppls experiences with duo problems and fixes, but none really fit what was happening on this one.
So I kept thinking about how it was just like a hu problem and went back and started really looking at the connector, clean, the pins to the mobo, no shorts from solder blobs or component leads cut and landing in a bad spot and not getting cleared out from the wash etc. Then I spotted a possible issue:

Meter confirmed continuity, crap, the solder mask apparently wasn't enough to stop what was prolly a super sharp cap lead and it was messing with the signal trace.
In the end an easy fix, but man was I frustrated for a long time...

[turbokon]

Sometime something so small can be easily overlooked. Congrats bro for finding the problem and fixing it.

[Drakon]

I've done stuff like that in the past.  I accidentally bridged the green line in my supergun to something else so I basically lost the colour green.  My duo when I added s-video for some reason the luma line broke connection so the s-video image was going in and out of working.  A little resolder and all was good, it just happens like that sometimes.

When wiring up eproms to superfx carts sometimes I'd have a connection or two not working....so I made this:



You need patience for this sort of work.  But if you have enough patience it usually works out.

[NightWolve]

Cool! Congrats! So another Duo saved from extinction!

I guess I've decided to use the electrolytic capacitor kit that I just bought for the component mod to do a full cap replacement while I'm at it as well. I'm not steve, and you need some expertise when replacing with more expensive ceramic/tantalum caps, plus the higher cost would be hard to justify. I did a full cap job on my SNES with ceramic/tant, just 12 caps, $11 bucks with shipping and I got some weird results with the Luma output afterwards... I'm not confident about that idea no more, but anyhow.

Drakon, I see you have an image of a SNES board with SRAM. Does that chip match the 2 Sony RAM chips on a SNES mother board by chance ??

[burn_654]

Yeah, I had many nights of headscratching over a stuck duo until I found a bit of damaged trace. It's easy to overlook.

That's an interesting diagram Drakon...I was looking into some snes repro'ing, may just have to file this for future troubleshooting

[jelloslug]

I had a problem like that when I put new caps in my TE.

[thesteve]

spotting this sort of thing is really just part of the job.
its quite commmon on region mods to have shorts or loose wires prevent boot

[Drakon]

Man you have no idea how helpful that guide is.  Wiring surface mount to dip is easy to mess up so it's really handy to be able to test that you didn't break a solder pad.

Yeah, I had many nights of headscratching over a stuck duo until I found a bit of damaged trace. It's easy to overlook.

That's an interesting diagram Drakon...I was looking into some snes repro'ing, may just have to file this for future troubleshooting

The worst is when something you mod works for a while and then fails randomly.  I had a couple of caps blow on my av famicom audio circuit, even though they had worked fine for a month or so.

[HercTNT]

spotting this sort of thing is really just part of the job.
its quite commmon on region mods to have shorts or loose wires prevent boot

So true. steve just got done fixing my duo with just such a problem.
Congrats on saving another duo!