Capacitor help (calling all EEs)

[Len]

Been having big problems with my FIC 503+ mb for a while now. Just discovered the problem. A capacitor near the CPU that I bent over so I could install a GORB on my K62 finally broke. I think I can handle soldering in a new one but I have a problem ...

The original capacitor was 6.3v 1500 uF. The only replacement ones I could find were 470 uF, 1000 uF and 2200 uF, all 16v.

Which one should I use? I know the higher voltage isn't an issue. Should I go with the 2200 uF? Is it possible to combine the the 1000 and 470 to get 1470 which I would think is close enough to 1500? If it is possible how should the two capacitors be connected? Series? Parallel? Pos-to-pos & neg-to-neg? I have no idea. TIA.

 

[Yomama]

It's a while ago that I learned this stuff, but I remeber that capacitors have to be in parallel to enhance the capacitance. I do not remember what happens when they are in series though. Anyhow you should be ok if you put the 1000 and the 470 in parallel, as that should give you about 1470. Don't worry anout the missing 30 uf, that's only 2% and most of these parts an circuits are designed to have tolerances of 10% and more.

Yo

 

[Hoot]

If it's near the socket, there's probably a good reason. Typically to filter and decouple one of the CPU voltages. Given that scenario, I'd go with the 2200uf. I have added capacitance (in parallel) to the different voltages that my CPU uses in an experiment to see if that enhanced stability. Unfortunately, it didn't, but the lesson also learned was that having slightly more capacitance than the board was originally designed to use was not detrimental to performance either. There are certainly some circuits on a motherboard where an exact value of capacitance it essential. Given the value tolerance of electrolytic capacitors and the fact that the one you trashed was 1500uf, chances are very good that it is not in one of those circuits.

Hoot

 

[Len]

I soldered on the 2200 uF capacitor last night but unfortunately the computer is still having the same problems. Nothing has changed since adding the capacitor. No improvement at all. I'm going to try a reinstall of Win98 just to be sure.

Is it possible that running the PC for a couple weeks with the broken capacitor has caused permanent damage to some part of the motherboard?

 

[Hoot]

That is definitely a possible scenario, but my gut feeling is that you have some other problem. It only takes a small, subtle problem to stop a complex beast like a mobo. Reseat everything; Clear the cmos; Reload your parameters; Try again. Maybe, if you have a digital multimeter handy, check the PSU output voltages for DC and AC content.

Hoot

 

[JimmyG]

You need to replace the capacitor with an exact replacement. Most circuit designs are called "point" designs and changing the value of one part can make the entire circuit unstable. Try to duplicate the manufacturer too! Even changing the manufacturer of a part can spell doom. Try the link below for a source for parts:

https://search.newark.com/product_search.phtml

 

[wolfman]

2 capacitors in series of the same mfd and voltage half the mfd and double the voltage rating. +to-. tying them +to+ creates a nonpolarized cap. same ratings or -to-.

 

[Deviant]

Wolfman is wrong about the non polarised capacitor. It will work for a while but there is a problem. Electrolytics have a high value of capacitenance for their size, because they use an thin oxide layer as a dielectric medium. This needs a correct polarity of voltage to stay formed. When reversed it breaks down over time. Also an electrolytic dielectric can break down after a long period of storage if a correct polarity charge isn't applied to reform the oxide layer.

 

[proze]

personally, i'd put the 1000 and 470 in parallel to get my 1470... the voltage is fine, you needn't worry about that. the caps are definitely electrolytic (on my mobo anyway), so just make sure you solder both +s and both -s to the right nodes.