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iMac G3 - Bulging Capacitor? C905 on the Power Supply Board v.2
Posted by: Alex on 2017-10-01 02:46:07
Hi

I just need a second opinion and potentially a little help locating a part.

I am taking apart an iMac G3, cleaning and inspecting after I found a compromised battery. While going through the process I discovered that the largest capacitor on the Power Supply Board, Ver. 2 appears bulged to the touch and visually. Now, I did try to locate this part and it appears available in bulk which I don't want, I only need one but I was thrown off by the 400wv designation. What does wv mean?

Could someone confirm if this is indeed a bulged cap and if you think it is, where can I find one?

It reads SMH 470uF 400wv (M) 85°C (location is C905 on the Power Supply Board v.2)

Pics of the cap.

IMG_0804.jpg

IMG_0799.JPG

IMG_0802.JPG

Thanks in advance for your expertise advice.

Kind regards

—Alex
Posted by: IlikeTech on 2017-10-01 04:50:17
WV means working volts, so you probably want to use a 500 ish volt cap.

Try these:

http://www.mouser.com/Search/m_ProductDetail.aspx?United-Chemi-Con%2fEKMZ451VSN471MR40S%2f&qs=sGAEpiMZZMsh%252b1woXyUXjyU7r8F9vEKYsDDe%252b4Sy6oE%3d

http://www.mouser.com/Search/m_ProductDetail.aspx?United-Chemi-Con%2fEKMZ451VSN471MQ55S%2f&qs=sGAEpiMZZMsh%252b1woXyUXjyU7r8F9vEKYXpdYFqx6Hbs%3d

Be sure to check the dimentions of the cap you are replacing.
Posted by: joethezombie on 2017-10-01 05:54:11
I’m not so sure that guy is bulging. Some of the larger caps have a vinyl cover over the top hiding the actual can. Since i see no venting lines, I would imagine that is the case here. if you press down on the top, does it spring back up?
Posted by: Alex on 2017-10-01 08:22:43
Hi joethezombie

In fact yes, pressing down on the cap does a little bounce back in return.

How could I test the cap to ensure it is working. I am waiting for my first multimeter to arrive. It's a cheapo until I can afford a proper Fluke. Any tips on testing it? Do I have to desolder it to test it? Yes I am truly basic with multimeters. I plan to learn cause it's just so cool to know.

Thanks IlikeTech, I appreciate the links.
Posted by: IlikeTech on 2017-10-01 08:54:13
Yes, you do have to desolder it, because you can't test in circuit.  Also, the proper capacitance does not mean it is not leaky.

No problem for the links! 🙂

Posted by: joethezombie on 2017-10-01 11:23:10
That big capacitor is probably the very last one that I would suspect as bad.  In my experience, it's always the smaller guys that start leaking.  If you're not having specific issues with the supply, I personally wouldn't change it out.  But IlikeTech is right.  To properly test it, you'd have to remove it.  And at that point, why not just replace it.
Posted by: Alex on 2017-10-01 12:38:31
Iliketech

I am curious, you appear to suggest that a cap can be leaky even if it measures ok. This could mean that caps are leaking without knowing it. With the analog/video boards taken out is there a sort of test to check what might be leaking but not yet detectable. I would think that perhaps putting a piece of paper or a toothpick or some other small probe that could absorb a stain could be one way.

I have often heard that bulging is a sign of a failing cap, thanks for the added tip joethezombie.

I can't test the entire computer until I get the replacement logic board that I just purchased on eBay. Hopefully it will all be ok. This machine is pretty old now, 1998 or so, I imagine changing caps on machines of this vintage is probably a worthwhile investment. Thoughts? 
Posted by: IlikeTech on 2017-10-01 16:10:19
Leaky in multiple ways. They can leak under the cap itself, but they can also leak voltage. I don't know much about that but I know it is a problem with tube equipment. I don't know enough to tell you if it is a problem with this. Chemicon makes good caps, so I'm not sure I would worry about that one. I would, however change caps if I has a problem when you get your new logic board.
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