Plaguey capacitors on PC mainboard.

[Etaoin Shrdlu]

I know there are some people with good electronics knowledge here, so I thought I'd ask. I've a Dell PC, maybe 8 years old. I don't want to throw it out, because it's 64-bit, and I'm a bit short of 64-bit stuff. But it keeps resetting itself, even with a newly-installed OS. I've tried reseating everything, which usually works for me, but not this time. There are about 6 leaking caps on the board. Has anyone here ever managed to repair a resetting PC by replacing such things?

[Martin Brown]

Yes. But it isn't for the faint hearted. I have done it once myself.

Are the capacitors actually leaking vital fluids or just deformed, bulging and at a rakish angle.

Try running a memory test to see if that is the root cause. The local memory capacitors seem to suffer the greatest stress on the motherboard.

Getting them out is interesting and inserting new ones into the vacant positions even more so. If you are experienced at soldering and have a decent iron and a steady hand then you stand a sporting chance of success provided you take antistatic precautions. Otherwise you will finish it off. See the thread about Electronics Advice for details.

Basically you need the right grade of high ripple capacitor at the right dimensions voltage and capacitance.

Not sure I would bother for an 8yo motherboard though. You can probably buy something faster than it from the likes of Morgan for ~£100-200.

[fred]

In article , Etaoin Shrdlu writes

Yes :-)

Whether you can do it yourself will depend on your skills with a soldering iron and your desoldering techniques.

Mobos are particularly tricky as the pcb designers break design rules by not placing thermal reliefs around cap pads (they use plain copper fill) which requires a lot of heat and good technique to repair.

I have access to good quality temperature controlled soldering irons of between 45 & 60W which I regard as essential for work of this kind.

I'm not one of those who advocates tacking caps onto pads as I believe the lead length will result in supply noise and reliability problems.

Quality caps can be had for under a quid each from CPC et al, as described in the recent 'Electronics Advice' thread.

I wont go into method, there are plenty of guides on youtube.

[Etaoin Shrdlu]

Okay, thanks chaps, I'll try it. I know it's not going to be fun, and could easily have been persuaded not to bother. I've done loads of soldering over the years, but yes, it has got much harder as I got older, more short-sighted, and things got smaller and more packed-in.

I've a pair of head-worn magnifiers, which helps immensely, but makes you look rather odd. And will use the small pointy bit for the Antex, of course.

[Etaoin Shrdlu]

Bulging at the top, and there is black crusty stuff around what look like cuts into the top face. There are four affected ones near to the CPU, and two near to the memory.

I always try and fix. I'm that mean :-)

[Etaoin Shrdlu]

I've an old Antex X25, and using it with the pointy bit seems to transfer much less heat at the end, in addition to it being more accurate.

[Brian Gaff]

Do you mean Sprague? They make caps. Well I guess you could try as they at least are not surface mount. Have you measured voltages or put a scope on the lines to see if its crud that is doing it? Resetting tends to usually be ram though.

Brian

[Etaoin Shrdlu]

I was referring to a phenomenon that became known as Capacitor Plague.

No, I'm just picking on these first as there is obviously something wrong with them.

I've put known good RAM in from another machine.

[fred]

Yep, a pointy tip wont help and 25W is borderline anyway for a filled power plane (huge heatsink).

In that situation, it may be that lying radial caps flat and tacking onto existing leads with them as absolutely short as possible may be the way to go. I absolutely hate it but sometimes you have to work with what you are given. If you go this way then cut away the body on the top side and leave the leads behind. The electrolyte is nasty so keep it off your hands or wear latex gloves.

Feel free to post your intended cap choice for a crit before buying but the Rubycon range from CPC reference in the Homeplug repair thread look very good.

[Etaoin Shrdlu]

I already have some with Nichicon on them, but I've no idea if they're any good. In the past, if I needed something like this, I always bought a few more. I don't have enough to replace all the ones I'm looking at here, but I thought I'd try the ones that look the worst first.

[John Rumm]

Yup done a few where they were odd form factors and hence difficult to replace.

Success rate around 75% - had some where in spite of having dodgy caps, replacement of those alone did not fix the problems.

[Etaoin Shrdlu]

Thanks, that's a good FAQ. I did get a cheap ESR (like £20) meter off eBay, but haven't had time to work out how to use it. The instructions, obviously written by someone in the Orient, are beyond me.

[Harry Bloomfield]

fred brought next idea :

If looks are not important - just burst the caps open, remove the debris and tack solder to the remnants of the legs.

[Stephen]

Talking of caps, I personally go for Panasonic FM and FC series. Can be got from the likes of Mouser, Digikey and Farnell.

[Etaoin Shrdlu]

That's interesting - I'll remember that for an emergency. Anyway, I've replaced about six of them. It's booted into the OS okay - I'll see how long it stays up.

[Etaoin Shrdlu]

The nackered ones I've taken out are Rubycon.

[fred]

In article , Stephen writes

Checking again, my main stock here is Panasonic FM which they interestingly claim has "40 % to 70 % lower impedance than FC series".

[fred]

Hah!, that'll teach me. As mentioned in another reply, on checking again, my main stock is Panasonic FM series. They appear to be better spec than either their FC or FK series but at the expense of case size. Again avail from CPC or RS Online.

The Rubys do still look to have a good spec.

[Etaoin Shrdlu]

Well I reckon anything would be better than what was in there before. Anyway, I changed the six worst-looking ones (one was an 1800uF that I replaced with a 2200uF, because that was what I had most of), and it's been running for a few hours now, which is longer than it managed before.

Of course, it might be just down to taking it apart and putting it back together again.

The pointy bit was good for clearing out the holes (used with a solder sucker), but useless for actual soldering in this application.

[John Rumm]

Well if you are measuring the cap out of circuit, you simply compare the reading with the expected value of ESR for the cap. A reading similar to that expected or lower is generally good. Higher usually indicates that the cap is failing. Some meters will also report other states such as open circuit or "leaky".

You can get the expected ESR values from the makers data sheet for the cap, however I have added a table here:

Which has typical values for standard electrolytics. You can use these as a baseline.