iMac G5 gurus - Please help - C903 keeps bulging

[Player2]

Hello all,

I've been reading the forums here for some time, and I've acquired a great deal of knowledge here. This is my first time posting though.

I've got here two iMac G5 motherboards, with ambient light sensor, no iSight. Part no. 820-1747-A. I recapped both of them with Nichicon HZ caps. After running each of them in a test computer for 24 hours, both of them are bulging the same cap. The location in question is C903, in the grouping below the RAM slots. Value is 1800 uF @ 6.3v. I replaced the cap again on the first board, tested again, bulged again.

Is this a common problem? Is the silk screen on the board wrong? I am positive that I installed the cap correctly, according to the board. Any help is greatly appreciated!

[kc8adu]

Re: iMac G5 gurus - Please help - C903 keeps bulging

fire it up and check voltage at these caps.check polarity too.

[Toasty]

Re: iMac G5 gurus - Please help - C903 keeps bulging

Pictures of the failing caps area please. Pull the cap(s) and get a clear pic of the board silkscreen also.

There should be plus(+) signs on the board. The stripe on caps is the negative(-).

Looking at the board with the RAM to the right with the caps below, if this is the version with the coil to the left of the caps, then both those caps should have the striped side pointed towards the RAM slots.

Check your power supply also. If it's from the same pre-2006 batch, it will probably have blown caps also.

Toast

[Player2]

Re: iMac G5 gurus - Please help - C903 keeps bulging

Thank you both for your replies. It turned out I did reverse the polarity (three times! ) There is a + symbol on the - side of the cap, however it was for the small cap immediately adjacent which I did no replace. It's working fine now. If only all manufacturers would just shade in the negative side of the pad...

I did replace all of the caps in the PSU as well and it's working great.

[ratdude747]

Re: iMac G5 gurus - Please help - C903 keeps bulging

Good job! imacs are not cheap... drop some cash on caps and you have a better imac than a brand new stock one could ever be. should be just like you first got it.