Replacing Capacitors... - RC-Monster Forums

rawfuls · 10:54 PM

Going to endeavor into replacing a few capacitors, on a computer motherboard.

But need some insight to guide myself which capacitors to get.

This is going to be more of an experimental thing, considering it's a Pentium 4 motherboard, but hey, old computers are fun to play with!
And to keep myself busy during my Spring Break..

Took a few snaps of the ones I'm working with.

Ideally, I'm going to be replacing all the ones that look bad to ME, so ~16 caps in total.
Probably going to stray away from Radioshack because of the cost..

So what's the rule, higher uF, same voltage, or...?

Pictures:
http://s53.photobucket.com/albums/g6...%20Capacitors/

brijar · 04.03.2012, 11:24 PM

I just got done working at a place that fixes computers and they had me replace any of them that were even slightly round on top, as well as the ones that had stuff coming out the top. There were actually only two different types to replace, so we just had a large bag of those exact rated caps.
It seems to me that you should try to get ones with the exact same capacitance (uF) and the same or higher voltage rating. I'm not sure what to do about the VAR rating, if those even have that rating. Shouldn't be too hard to order a few from Digikey or even eBay that have the same ratings. Radioshack is definitely too expensive for that many caps.

rawfuls · 04.03.2012, 11:26 PM

Is going up higher uF going to do anything, versus going up higher voltage?

brijar · 04.03.2012, 11:32 PM

I don't know if the motherboard uses those caps for timing or for filtering. If they are used for timing, then changing the uF would throw it off. If they are just filtering capacitors, a small change in uF wouldn't be too detrimental I think. But since I am unable to tell from looking at the board, I would try to get the same uF or maybe a tad higher. But the same is ideal.
As far as I know, a higher voltage rating wouldn't affect it too much. It would probably just be a slightly bigger capacitor. It would change the resistance some, I think, but I'm not sure if that would prevent the board from operating.

See if you can find the ratings on those capacitors. I doubt it will be hard to find that exact rating on digikey.

rawfuls · 04.03.2012, 11:49 PM

Looks like i'll be searching for exact uF and voltage.
Since it's a little hard to tell with it still attached to the board, I plan on diagramming which I cap I pull from where, and to write the exact specs.

Hopefully I can finish it within this spring break and have a working P4 board.

brijar · 04.04.2012, 09:41 AM

Yeah that's a good idea to take a picture of the whole board and label each cap in the picture as you pull it out. You might save the picture in two different locations (flash drive and hard drive), just to be safe haha.
I found that rocking the caps out was the easiest and quickest way to get them out. I also rocked the new ones back in after trimming their leads shortly, since I wasn't very good at cleaning the holes with solder braid.
Be sure you note the polarity! The stripe/arrows point to the negative side of the capacitor. Good luck!

BrianG · 09:40 AM

Just a warning in advance; replacing caps on a motherboard is a ROYAL PAIN! There are several layers of copper, some of which are ground/power planes, so the board tends to wick away soldering iron heat fast. There is a fine line where the heat/power needed to remove caps is pretty close to the amount that will damage nearby components. To help minimize heat build-up, work on different sections between each cap removal/replacement.

As far as the capacitance/voltage rating: Very few caps (if any) are used for timing on a motherboard. The frequencies/duty-cycles needed are very precise and caps just aren't accurate or stable enough as they tend to "drift". Besides, timing caps are generally not electrolytic but are ceramic, tantalum, etc. So I would be 99% certain that all those electrolytic caps are for filtering.

Like was said, going up higher in voltage or capacitance shouldn't cause any problems, but they do get physically larger/taller which may interfere with other components, heatsinks, etc. So do try to get close to the same values, but do not go lower. No matter what, make sure they are low-ESR type (105ºC rating).

Good luck!

BrianG · 04.04.2012, 09:47 AM

On the one mobo I worked on, I used a sharpie and drew numbers on the top of the caps I wanted to replace, and then had a piece of notepaper that had those numbers and the rating of the caps. After doing it once, I will never again replace caps on a mobo. For the amount of time I spent on the thing combined with the price/shipping of the caps, I could have gotten a new mobo.

rawfuls · 04.04.2012, 11:54 AM

I've resoldered caps before, but only once or twice, so I wouldn't really know.

In any case, picking out caps was harder than I expected..
http://search.digikey.com/scripts/DkSearch/dksus.dll

so many options. LOL.
Which should I generally go for?

As an example, I used 3300uF & 6.3V, which are the ones right next to the processor.

BrianG · 04.04.2012, 12:30 PM

At the Digikey site, scroll down to "Capacitors" (of course), and select "Aluminum".

Then, select your filters:

- 3300µF
- 6.3v
- "through hole" mounting type
- Up to 105ºC rating (to select multiple options, click on one item, then hold the Ctrl key while selecting the others)

Click the "Apply Filter" button.

If the list is still too long for you, you can narrow it further by selecting acceptable physical sizes you can use.

BrianG · 04.04.2012, 12:33 PM

Another thing; you might want to Google "motherboard capacitor replacement kits". There are places that specialize in this type of thing and would have the right parts (or links to the right parts).

rawfuls · 01:25 PM

It's one of those old generic Elitegroup motherboards, but I will definitely try.

P4PB400 Caps...

Edit:

Finished removing all the caps, and left them all numbered.
Main issue i'm having is removing all the solder to make a perfect hole ready for a new cap.
Going to see if I can find a stainless steel pick, or maybe some tweezers..

Will probably order caps by tonight.

rawfuls · 02:10 PM

Here they are:

(4) 1500 uF 16V
(7) 3300 uF 6.3V
(5) 1000 uF 10V

from the looks of it, looks like I'll be needing these:
3300uF Cap:
http://search.digikey.com/us/en/prod...MPM-ND/2428105

1500uF Cap:
http://search.digikey.com/us/en/prod...1780-ND/756296

1000uF Cap:
http://search.digikey.com/us/en/prod...113-ND/2796072

Totaled to: $18.13, after shipping and tax, a little over $20.
More than I wished... but hopefully this will pay off.