Please help a failing brain!

[Loose rivets]

I removed the 3300 mic capacitors from my HP PC motherboard, and set about finding replacements locally. I may as well have moved to the middle of a desert. I won't bore you with the bizarre conversations I had in Tex-Mex.

It has to be said my short term memory is failing me. The caps would be the same as the other ones on the PCB . . . right? White circle to the negative stripe? Not on this HP. I looked in dismay as I realize I'd made an assumption.

This site is unequivocal. Neg to the semicircle of white. The 640 is the opposite on all the others, and I'm not sure about the ones I took out.

:ugh: :ugh: :ugh:

Yep, I beat myself up a lot these days.

Capacitor Lab - Types of Capacitors - Radial Electrolytic Capacitors (http://www.capacitorlab.com/capacitor-types-electrolytic/)

Can't find any good specific pictures of the actual MB. Pavillion a 640n

Anyone know for sure?

[Bushfiva]

Negative stripe to the white semcircle. On the motherboard I'm looking at, there's also a plus sign near the opposite half of the circle for most of the board markings.

[Loose rivets]

I was so flummoxed, I went back for a third look. No question, all the white stripes with a negative sign on them are on the Opposite side to the white semicircle.


Looking on the web, I now see the 1.5 gig I've been using for years, can't possibly work. I gig max.


The thing is, this little HP is astonishingly well built in terms of case structure, and indeed is reasonably fast - considering. It is almost perfectly silent, the fan only giving a burst during startup. It then cruises, despite the room being at 80 f most days.

Using this much higher spec Foxconn board and a new drive is like being a visitor in a strange land. I want my little HP back.:{

Anyway, the caps wont be here for a few days, as they have to be shipped from the real world to this cactus infected oven. One last bang before bedtime. :ugh:

[Milo Minderbinder]

If its of any use, the motherboard in that would appear to be an ASUS K8N8X-LA (Diablo)
Just done a search, but can't find any images good enough

Motherboard Specifications, K8N8X-LA (Diablo) HP Pavilion a640n Desktop PC - HP Customer Care (United States - English) (http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&cc=us&dlc=en&product=426323&lang=en&docname=c00064822)

[Loose rivets]

Thanks for the link, I'll keep that handy.

I did find one HP board in the early hours this AM One could JUST see the marking on one cap the way they are on mine.

Could HP have marked the MB against convention? Also, after many sites confirming the convention, and in the dead of the night, I began to wonder if they'd all been put in the wrong way round!

(There are about 20 more with this reversed marking.)

Because electrolytics of this capacity are difficult to check with an AVO 8, I got inconclusive results from charging the one good condition one. (of 6) It did however, charge in the correct direction, and maintained voltage when measured with a DVM. Whereas the messy ones seemed to have reversed and furthermore, leaked in both directions. This reversal thing rings a very, very distant bell. It just makes more :confused: when trying to be certain.

Should have been such a simple little job - assuming non of the other MB layers are allowed near the full-thickness holes. They wouldn't do that, would they?

I

[Milo Minderbinder]

"They wouldn't do that, would they?"
this describes how the caps are fitted into the board
Badcaps.net - Cap Removal (http://www.badcaps.net/pages.php?vid=32)
They do connect to various layers but it seems as long as you have solder IN the hole - no gaps - you should be OK. Also read the link you posted yourself above re the fitting


Re the board labelling
see this
Badcaps.net - Cap Installation (http://www.badcaps.net/pages.php?vid=33)
Don't forget your board is made by Asus

".....If you look at the marking on the motherboard where the old capacitor once resided, you will notice a 'half moon' white shaded area there. The lead that is in that white area represents the NEGATIVE pole of the capacitor. On the actual capacitor, the negative side is clearly marked with a 'minus' sign running down the NEGATIVE side. ..........
This does not always hold true on all motherboards! Some boards, especially most Asus boards, are reverse marked on the silkscreens, the 'half moon' area is actually the POSITIVE pole!! Pay attention to the markings on the board AND the markings on the original caps as you remove them!! As a rule though, the white shaded area represents the NEGATIVE pole, just make sure you check yours as you remove the old caps!"



and from Capacitor Lab - Types of Capacitors - Radial Electrolytic Capacitors (http://www.capacitorlab.com/capacitor-types-electrolytic/)
"Not all PCBs follow this rule though. ASUS actually uses the white shaded part to indicate the positive lead on their PCBs, which is quite confusing."
............................................................ .......

For interest, theres a dedicated bad caps forum at
Badcaps Forums - Salvation For Your Hardware! (http://www.badcaps.net/forum/index.php)

and heres another long forum thread on the topic of bad caps in PCs
The Mother Board :: View topic - Bad bad capacitors (http://www.motherboards.org/forums/viewtopic.php?t=101830&postdays=0&postorder=asc&start=0)

[Loose rivets]

Superb links. Thanks very much. Glad to know I'm not inverting my opti-neurological-physiology. :eek:

Wish I'd ordered my parts from him.

And WALLA!! You will have a clean . . .

And the bloke's obviously Canadian! :p