Beware of Bad Capacitors (source of much bizarre behavior)

[motech]

I've run into 2 motherboards in the last month that had
bad capacitors on them (Bulging, Leaking or both) that
was causing wierd power problems, and startup problems.

I heard about this one on the web about 6 months ago, yet
haven't seen anything personally until just now.

One mb was a Gateway OEM board.

Just giving everyone a heads up again on an old issue. ;)

[TallCool1]

I've run into 2 motherboards in the last month that had
bad capacitors on them (Bulging, Leaking or both) that
was causing wierd power problems, and startup problems.

I heard about this one on the web about 6 months ago, yet
haven't seen anything personally until just now.

Here's a posting I wrote a little while ago...

I have been an electronic technician for forty years and a computer technician for about 25. I am considering putting together a Guide to Replacing Motherboard CPU Capacitors -- but until then I will share some tips. Please be sure to read this guide IN ITS ENTIRETY before proceeding.

I STRONGLY recommend the use of Panasonic (Matsushita) FC series electrolytic capacitors. Why? Not only are they the best available, but they are quite easy to obtain from Digi-Key http://www.DigiKey.com.

I have done business with Digi-Key for over 30 years. During that time, over 90% of the elecrolytic capacitors I have purchased for repair and fabrication have been Panasonic from Digi-Key.

The FC series are low equivalent-series-resistance (low ESR) 105-degrees-C capacitors. This means that the high ripple currents that flow through them in this application not only flow more easily (a Good Thing), but also that less of this current is dissipated as internal heat (also a Good Thing). "Normal" capacitors are rated 85-degrees-C and are just not up to this kind of stress.

Use a 30-40 watt soldering iron. I also recommend the use of the Radio Shack catalog number 64-2060 45-watt Desoldering Iron with the catalog number 64-2062 Heavy-Duty Desoldering Tip (tip erosion happens rather quickly with the stock tip; the heavy-duty tip is iron-clad and holds up well). You need LOTS of heat to desolder the caps, as a motherboard is a multi-layer printed circuit board (PCB) with a large area of copper as a ground plane. I also recommend the use of 63/37 eutectic-alloy solder for best results, though 60/40 is OK too. Digi-Key has the solder, as well. If a group of guys with the same problem pool resources, you can buy the caps in bulk and share the tools and solder.

Make sure that the caps you obtain for replacement match (as closely as possible) the originals' physical size -- measure them. In the values these boards use, they are available in two styles -- short & wide and tall & skinny. Most boards use tall & skinny. Typical Digi-Key part numbers are P10202-ND for the "tall" 1500mFd/6.3V cap and P10204-ND for the "tall" 2200mFd/6.3V cap. This will give you a starting point for a site search. You can also download all or parts of the Digi-Key catalog in PDF format.

Practice, practice, practice! I recommend that you get a hold of a scrap motherboard (especially 486-based or later) and work with it until you feel comfortable enough to move on to the real thing -- it's REALLY easy to damage a PCB with excessive heat. Here's the procedure that I have used in the past:

* Using the soldering iron, add a little solder to each of the connections that you will later UNsolder. This ensures a vacuum seal and good flow for the desoldering tool. This also reduces the need for added rosin flux.

* Using the desoldering iron, carefully remove the solder from each connection. Give the joint enough time to melt all the way through, but not enough to burn the board -- this is where the practice pays off. Be sure to clear the solder from the iron's nozzle after EACH connection.

* Once the connections are unsoldered, GENTLY rock each of the caps to ensure that they are unsoldered BEFORE pulling it out of the PCB (there's not much in electronic repair that's more disheartening than pulling up a trace along with the part). If it's still stuck, try applying the soldering iron TO THE LEADS ONLY while rocking the cap to free it. If it's STILL stuck, add solder to the connection and desolder it again.

* If a capacitor leaked crud from the bottom instead of venting, all is not lost. Get some distilled water (best, though tap water will do) and mix it with baking soda (the electrolyte is basically boric acid). Apply the baking soda solution to the affected area and scrub (gently) with a toothbrush. Rinse the area with clean water (carefully, don't let the bicarbonate spread around), blot dry with a cloth or paper towel, then use compressed or "canned" air to blow water from under components. Follow this up with 91% or 99% isopropyl (not methyl) alcohol on a cotton swab (a good source for this is isopropyl drygas -- Iso-Heet, for example -- which is available at auto parts stores); this will remove rosin flux and other impurities. If the drygas has a skull-and-crossbones on it, it contains methanol and should not be used.

I think that's enough for now, except to say, "WATCH POLARITY!" Reversing polarity on a high-value electrolytic capacitor can cause the device to explode -- literally. The board is clearly marked, but a diagram is STILL a good idea.

Disclaimer: The user assumes all responsibility for the results of this guide. I am not responsible if you damage or burn up your board, or if it fails to work once repaired.

[motech]

Exactly the information I want for when I get a chance
to fool around with that stuff!!

THanks :)

I don't think I would rate myself qualified to
do that and still have it reliable :)