radiounix wrote on 2020-12-15, 14:24:

Sure, but given a general lack of commercial repair services in the US, and a desire to keep equipment running a bit longer, you can reasonably expect people with minimal electronics backgrounds to attempt to do their own board level repairs.

I'm all for DIY and people can decide themselves if they can do the job or not.
It's just silly to start a project without the necessary tools. A cheap but usable hot air station costs $80 but it's absolutely vital if you want to work with computer parts. Replacing caps with a hot air gun feels like a dream compared to a soldering iron that can't even transfer enough heat to the solder pads.
If a cap takes 10 seconds to remove then it's absolutely pointless to leave known old/bad caps in circuit and risk damage to the board.
But it's just my opinion so people can manage their repairs however they prefer.

I have a hot air station, but for recapping I usually just heat both leads of capacitor with wide T12-K tip. Sometimes i just preheat the area with hot air and continue with soldering iron.

$20 T12 temperature controlled soldering iron with replaceable wide tip and DC power jack + 19V laptop power supply (and flux and/or fresh solder) is sufficient in many cases. At least it's much better than "... and now touch first pin, second pin, move the soldering iron back and forth, back and forth, wiggle the capacitor a bit" BS seen in some youtube videos.

adalbert wrote on 2020-12-15, 20:20:

I have a hot air station, but for recapping I usually just heat both leads of capacitor with wide T12-K tip. Sometimes i just preheat the area with hot air and continue with soldering iron.

Do you de-solder the holes or do you go straight to the re-insertion ?

douglar wrote on 2020-12-15, 20:32:

Do you de-solder the holes or do you go straight to the re-insertion ?

I re-insert caps without emptying the holes, but usually I wick away some solder from the top layer with copper braid and flux. Some solder still remains inside, but the holes are concave after that. It prevents capacitor leads from slipping away and makes it easier to insert them into the holes.

But if you need to remove the solder completely and you don't have desoldering pump, you can heat the holes and use stainless steel needle.

adalbert wrote on 2020-12-15, 20:44:

I re-insert caps without emptying the holes, but usually I wick away some solder from the top layer with copper braid and flux. Some solder still remains inside, but the holes are concave after that. It prevents capacitor leads from slipping away and makes it easier to insert them into the holes.

OK, great, thanks for the info/confession. I've only done one board and I did it that way and I felt guilty afterwards, but it was sure a lot easier to do when things are cramped.

The mobo also had a spot for a capacitor that was not populated. Probably not a good idea to populate it, I imagine. Or is it?

.

Not sure if this is too relevant to the discussion, but what kind of capacitors are these?

Up until now my recapping was limited to motherboards, but now I've decided to do some preventative maintenance on my AT power supplies and am not sure what to replace these with.

Munx wrote on 2020-12-16, 12:00:

Not sure if this is too relevant to the discussion, but what kind of capacitors are these?

Up until now my recapping was limited to motherboards, but now I've decided to do some preventative maintenance on my AT power supplies and am not sure what to replace these with.
P_20201216_105712.jpgP_20201216_105657.jpg

If you're talking about the reddish brown rectangular ones, I believe those are polyester capacitors.

Someone correct me if I'm wrong, but those rarely cause problems unless they are in a circuit where they are known to fail. I don't believe they degrade the way aluminum electrolytic caps do.

Unless there's a problem, I would only worry about aluminum electrolytic caps. Once in a while I replace a tantalum, but only if they cause problems (shorted or blown). If they aren't defective they last an incredibly long time. The only caps I always ALWAYS replace are Rifa X capacitors, but you likely won't find many of those in computers made after 1990. I've seen them in Apple iie power supplies, a Franklin 1000 and a Gridcase 386 industrial laptop from the late 80s (that one exploded... what a stink!). They can potentially be in some IBM PC\XT power supplies too, but the two I own have large polyester type caps instead.

Ozzuneoj wrote on 2020-12-16, 15:14:

If you're talking about the reddish brown rectangular ones, I believe those are polyester capacitors. […]
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Munx wrote on 2020-12-16, 12:00:

Not sure if this is too relevant to the discussion, but what kind of capacitors are these?

Up until now my recapping was limited to motherboards, but now I've decided to do some preventative maintenance on my AT power supplies and am not sure what to replace these with.
P_20201216_105712.jpgP_20201216_105657.jpg

If you're talking about the reddish brown rectangular ones, I believe those are polyester capacitors.

Someone correct me if I'm wrong, but those rarely cause problems unless they are in a circuit where they are known to fail. I don't believe they degrade the way aluminum electrolytic caps do.

Unless there's a problem, I would only worry about aluminum electrolytic caps. Once in a while I replace a tantalum, but only if they cause problems (shorted or blown). If they aren't defective they last an incredibly long time. The only caps I always ALWAYS replace are Rifa X capacitors, but you likely won't find many of those in computers made after 1990. I've seen them in Apple iie power supplies, a Franklin 1000 and a Gridcase 386 industrial laptop from the late 80s (that one exploded... what a stink!). They can potentially be in some IBM PC\XT power supplies too, but the two I own have large polyester type caps instead.

Thanks for the info. I guess I'll leave the polyester caps alone then. I'd still like to replace the electrolytic ones since I got some spares and the simple layout means it shouldn't be too hard.

Yeah, as long as you're sure there's nothing still holding a charge in the PSU, it's pretty straight forward to replace caps in one of those. Just be sure of polarity when installing new caps... match the polarity of the old caps, not the markings on the board. I've seen a couple devices over the years where the - line on the capacitor was clearly going into a + on the PCB, and yet it worked for 10+ years, so the markings were incorrect.

Also, I like to look up the series of whatever capacitor (like "nicon xyz") is in there and then compare it to what I have to be sure they are the comparable. You wouldn't want to replace low-esr caps with standard capacitors.

Miphee wrote on 2020-12-15, 06:43:

That's what I call a religious belief based on nothing, an argument for the sake of the argument. Not my problem, it's OP's decision.

Not a religious belief at all. Caps do fail at different rates for a variety of reasons. It is ultimately the OP's decision, but it's also worth understanding a little about how electronics reliability works so the OP can make an informed decision.

Ozzuneoj wrote on 2020-12-16, 15:14:

If you're talking about the reddish brown rectangular ones, I believe those are polyester capacitors.

Those are film caps. Likely not safety rated, so if the PSU has any in the voltage transient filter between the big primary capacitors and the power cord socket you may have an electrical hazard.

Ozzuneoj wrote on 2020-12-16, 15:14:

Someone correct me if I'm wrong, but those rarely cause problems unless they are in a circuit where they are known to fail. I don't believe they degrade the way aluminum electrolytic caps do.

Again, they can fail improperly in the event of a high voltage transient, although the one in the picture should be after the TVS device and therefore no problem. However, the presence of an unsinked four diode rectifier and missing filter choke makes me think the MOV/TVS diode is missing on this unit as well.

Ozzuneoj wrote on 2020-12-16, 15:14:

Unless there's a problem, I would only worry about aluminum electrolytic caps. Once in a while I replace a tantalum, but only if they cause problems (shorted or blown). If they aren't defective they last an incredibly long time. The only caps I always ALWAYS replace are Rifa X capacitors, but you likely won't find many of those in computers made after 1990. I've seen them in Apple iie power supplies, a Franklin 1000 and a Gridcase 386 industrial laptop from the late 80s (that one exploded... what a stink!). They can potentially be in some IBM PC\XT power supplies too, but the two I own have large polyester type caps instead.

I would classify Fuhjjyu as another "always replace" brand. Ceramic caps can also be problematic due to their tendency to fail short, but that's only a concern if the board is actually malfunctioning.

Miphee wrote on 2020-12-15, 07:27:

That doesn't mean that the rest of the caps (not just the leaky-bulgy ones) shouldn't be changed.

Which is why it's useful to apply reasoning to your decision. Do your best to estimate the condition of the capacitors based on all the information at hand. If you're unsure, pull some caps and test them, then make your decision.

I still have fully functional Chaintech motherboard with G-Luxon caps from capacitor plague era, which are considered to be incredibly crappy. All while I have two identical Gigabyte motherboards from the same era, with fancy Nichicon caps, which failed on spectacular level on both.

Ozzuneoj wrote on 2020-12-16, 20:57:

Just be sure of polarity when installing new caps... match the polarity of the old caps, not the markings on the board. I've seen a couple devices over the years where the - line on the capacitor was clearly going into a + on the PCB, and yet it worked for 10+ years, so the markings were incorrect.

According to badcaps.net, that would be Asus. But there could be others.

This happened to my T3200SXC PSU with 30 year old caps. I couldn't identify which ones leaked, because the entire board was covered in electrolyte. IIRC it used mix of Sanyo and Elna RSH LongLife capacitors for smaller caps and nichicon for big caps (rather good brands, as it is $8000 computer). I just cleaned that board, put into storage and fitted replacement PSU, as that seemed to be easier than repair. But maybe it's just broken soldermask and copper tracks would still be fine.

I wonder how often old/bad capacitors can cause this kind of damage to the PCB? Most of the time the electrolyte just seems to dry out and not leak on the board.

gdjacobs wrote on 2020-12-17, 17:07:

Which is why it's useful to apply reasoning to your decision. Do your best to estimate the condition of the capacitors based on all the information at hand. If you're unsure, pull some caps and test them, then make your decision.

My reasoning is simple: I want to do a good job. It's not mandatory to replace all caps on old boards, I just sleep better at night this way.
It comes from my CRT TV/radio repairing days where replacing all caps was pretty much mandatory because it solved the majority of problems.
I'm pretty sure that a bunch of unexplained stability problems could be fixed with a full recapping even if those caps looked fine.
I'm not going to convince anyone to spend money on an old mainboard and others are not going to convince me not to replace old caps.
I'll leave it at that.

Miphee wrote on 2020-12-17, 19:56:

I'm pretty sure that a bunch of unexplained stability problems could be fixed with a full recapping even if those caps looked fine.

Sure, caps are the cause of stability problems more often than not. If replacing the caps on your CPU power phases resolves the stability issue, there's not much incentive to change out the caps elsewhere. Swapping all caps isn't wrong per se, but it's money and, more importantly, time which I can spend elsewhere.

gdjacobs wrote on 2020-12-17, 21:30:

Sure, caps are the cause of stability problems more often than not. If replacing the caps on your CPU power phases resolves the stability issue, there's not much incentive to change out the caps elsewhere.

There is: it's hard to tell which one causes the stability issue. So either you start replacing them one by one or you replace them all and call it a day. I'm not going to leave 20 years old elcos and bad brands in a circuit when it takes maybe 30 minutes to replace them all. Money is not everything when it comes to repairs.

Miphee wrote on 2020-12-18, 07:59:

There is: it's hard to tell which one causes the stability issue.

It's usually easy to tell which group of caps contribute to the stability issue either based on logic or by pulling one or two from the set and testing them.

gdjacobs wrote on 2020-12-18, 20:09:

It's usually easy to tell which group of caps contribute to the stability issue either based on logic or by pulling one or two from the set and testing them.

Yes, if you are familiar with those groups. If not then it's easier to replace them all and ¢50 for a standard Panasonic low-esr elco is very cheap. It costs maybe $8 total to replace all elcos on a board, even cheaper in bulk. It's pointless to cut costs there.

Miphee wrote on 2020-12-18, 20:31:

gdjacobs wrote on 2020-12-18, 20:09:

It's usually easy to tell which group of caps contribute to the stability issue either based on logic or by pulling one or two from the set and testing them.

Yes, if you are familiar with those groups. If not then it's easier to replace them all and ¢50 for a standard Panasonic low-esr elco is very cheap. It costs maybe $8 total to replace all elcos on a board, even cheaper in bulk. It's pointless to cut costs there.

On a motherboard, it's pretty easy to know which caps are doing VRM duty as opposed to those installed for decoupling. On a PSU, you can always tell primary bulk caps from output filters. Knowing where the most electrical stress and poorest air flow is doesn't take a genius.

Replacing caps which are unlikely to fail in a human lifetime is, to me, nothing but pointless make work. I'd rather spend my limited time repairing components that have failed or having fun.

Replacing caps IS fun! 😉
It's a hobby after all, not a chore.