Resurrected dead motherboard (bad caps)

D

defuseme2k

[H]ard|Gawd
Joined
Oct 7, 2004
Messages
1,074
OK -- I've been through this a couple of times in various situations. I'm no eletrical engineer and in fact can take no credit here. Another active hardforum member and good friend of mine GoodBoy helped, or in reality, did almost all the work. I've searched the forums and around on the internet and apparently this just isn't that common of a practice outside of knowledgable electricians. There is SOME information out there though. Why I don't know, this has really proved to be worthwhile for me.

I had a dead system (obviously not my gigabyte ultra durable board :D). Not THAT fancy, but it was not something I wanted to throw away, plus I wanted to boot back into the OS to get data and look around to make sure I didn't miss anything. When I pushed the power button, the fans would spin for a second, a red LED lights up on the board, the fans stop and nothing more happens. After some closer inspection I notice 7 capacitors are bubbled up and some of them also had leaked. I had to stop and wonder if most people (most people... yeah what I mean is [H] people) at this point decide it is dead for good and take their losses? Anyway, after finding no noticeable burn marks or anything like that, I called GoodBoy up since we've done this before with success. You have to be extremely careful, but generally if you use the same type with the same or slightly higher voltage/capacitence it is OK just as long as the temperature ratings and such are at least on par with the original capacitor. Do your research first! What would have cost me hundreds of dollars to fix (it made no sense to find used parts or go super low end on new stuff), this was done for an hour or two worth of time and the parts (20-30 dollars worth). I guess cost also assumes you have time, a soldering iron, and all of the necessary tools (wick, etc).

Anyway, we heated the solder, pulled out the old cap, used solder wick / solder sucker to pull out the old solder, seated the replacement cap, soldered it in place, and then trimmed the excess from the leads. Rinse, repeat.

After all of the capacitors were replaced, I took it home, reinstalled it, and as expected from previous experience... it booted right up and has been running solid like nothing ever happened.

Anyone else do anything like this? I remember the huge thread about people baking their dead cards to reflow solder, but what about an obviously bad component?

--NOTE: I expect GoodBoy will probably post in here if any clarifications are needed in my post. As I said I'm not nearly as capable/knowledgable... it just happened to be my crap that died :(.
 
I have replaced a few capacitors on motherboards however I am an EE. Well at least I graduated with an EE and a CS degree in December 1996. I do not do much with my EE degree these days although I did have to provide maintenance for a few laser film digitizers about 1 decade ago. And for these I did have to use an oscilloscope to adjust timings and the response using potentiometers. I also had to replace an 1800 V dc supply, a galvanometer and a few lasers. Not much EE since then but 750 K lines of C++ code..
 
I've had only one mobo fail for something other than caps or MOSFETs, an ECS K7VTA3 v. 8. It just stopped during the flash of a CD writer and wouldn't restart. I thought the CD writer's BIOS was accidentally flashed into the mobo's ROM, but I mangled the mobo while trying to unsolder the ROM chip (with an iron and solder wick, not a heat gun) and forgot to read it before flashing it again.

Most of the cap-related mobo failures I've seen have been with the the voltage regulator for the memory chips, maybe because companies have been using better caps for the CPU voltage regulator.
 
I've replaced caps on motherboards quite a few times.

Back in the day I also bought a socket 7 board that had screwdriver slippage damage on it from the store I worked at. a few traces were messed up as well as a few surface mount caps and resistors were missing. I rigged it back up with all the traces patched and new surface mount pieces on it. It worked great for about 5 years or so before the board died.

I also have replaced bad caps in quite a few power supplies. I also replaced a voltage reg in a power supply when I was about 14.... that was sooo crazy long ago.

I've also fixed a few power bricks for video game systems, etc. Usually a cap or fuse is blown. cutting them open is the hardest part.

But yeah... replacing caps and other pieces usually costs me nothing except for a bit of time. I keep a stash of old broken electeronics to salvage pieces from when I need them.

I am not an electrical engineer either. Just learned from trial and error as well as doing a bit of research.
 
I've done this like 10 times now. Fixed every single one. In fact, one friend of mine will tell me, "that motherboard we fixed in like 2004 is still working!" every once in awhile. As far as I know every single one is still working. I used better quality caps, with higher uf and voltage ratings. 105c always.

I fixed my own server mobo, an old A7N8X about 2 months ago.

Fixed a guy at works 40 something inch LCD tv that had 2 bad caps on the power supply board.

Anything with large current thru the powersupply section and/or hot operating environment is going to be prone to caps bulging/leaking/exploding.
 
I've done a few motherboards and power supplies. I even bought a desoldering gun (Hakko 808) which helps tremendously if you use it correctly.

For the record I'm an EE, but doing this job is more about practice and technique than any special knowledge (other than how to pick the right replacement caps).

A good resource for this is here:

http://www.badcaps.net
 
Thats just some website selling a repair service. I know how to pick replacement caps.

Found some 10,000 hour mtbf @105C Panasonics from Digikey. Cost a bit more but worth it I think. In comparison some of the better Rubycon's are only ~2,500 hour rated.
 
I brought a 7600GS back to life twice doing this. First round 3 caps blew up, second round one more popped. So 4 replaced caps later, it's still running strong.
 
GoodBoy said:
Thats just some website selling a repair service. I know how to pick replacement caps.
Click to expand...

Yeah I've never used their service. The forums there are a good resource though. Lots of knowledgeable people, info on how to spot failing caps, what brands to look for/avoid, information on spec matching, etc.

Found some 10,000 hour mtbf @105C Panasonics from Digikey. Cost a bit more but worth it I think. In comparison some of the better Rubycon's are only ~2,500 hour rated.
Click to expand...

Yes the low ESR types, which are usually what you find around the voltage regulators, tend to have a lower MTBF. Combine that with the high heat around that area of the motherboard, and that's why these fail so often, at least up until everyone started using the solid state caps a few years ago. I haven't heard of any of these failing (then again, how would you know if one went bad...they probably don't bulge and leak like electrolytics).
 
My boss's 60" CRT projection set started having convergence issues. Ordered two new converge chips and about a dozen new resistors and spend an afternoon buried inside the tv. One month later it's still working fine! Finished that and he comes back with a 22" LCD that won't stay powered on. Cracked it open, saw a bulged cap, soldered on a new one and that has also been fine since.

One thing I will say is Radioshack desoldering braid sucks. Maybe my iron wasn't hot enough, but I had to constantly tin the tip of the iron to transfer enough heat through the braid to melt the solder point.
 
I did this for the ECU board in my old Dodge Stealth, saved several hundred dollars.
I have also replaced the Caps on the power supply board of a Samsung LCD that was flickering (apparently this is common with Samsung displays as they use cheap ass caps).

I agree that its funny these sort of repairs aren't discussed more as they are very cheap and you typically have nothing to lose on a component that is already broken.

Funny enough the only thing I have killed while soldering was a 1st gen Nano I was changing a battery in, damn two wires were too complicated for me.:p
 
Replaced the bad caps on my old VX922 monitor last year and the thing's been running like a champ ever since (very common problem with these monitors; google "VX922 bad caps").

I'm also contemplating replacing the STK chips in my parents' old Hitachi projection TV. It's starting to get the infamous convergence issues that cannot be fixed with the built-in "Magic Focus."
 
You must log in or register to reply here.
Back
Top