I have some questions on replacing capacitors on the iMac G5 Logic Board

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MaxTek's picture
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Joined: Dec 20 2003
Posts: 702

I just got (for free) an iMac G5 17". Appears to never been opened. Ram, hard drive, airport extreme card, optical etc all present. Upon booting, I get all 3 lights on the motherboard. Fans spin normally, hard drive spins normally etc.

I can very slight images on the screen. I also see widgets pop up and down when the key is pressed on the keyboard.

After inspection of the logic board, I can see 3 caps that are bulding, 1 of them is leaking. It has half K caps and half of the + caps.

Apple's knowledge base says the LCD is bad since all 3 lights are lit on the logic board but the LCD is dark. My inclination is the 3 bulging caps.

So my question is about installing new caps. Taking apart the iMac is not an issue. I have dismantled many, many Apple products. But soldering is a different story.

Is it possible to do, if a person has never soldered on a logic board before? Will I find the right kind of solder and gun at Ratty Shack?

What do you think, and if you have a good step by step website please post it.

Thanks.

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eeun's picture
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Joined: Dec 19 2003
Posts: 1891
Sounds like you're replacing

Sounds like you're replacing components on the LCD portion of the board. It's a weak point for LCD monitors in general, and I've so far repaired about a half-dozen 'dead' LCDs by swapping out caps.

If you Google for replace LCD capacitors there's a bunch of tutorials.

A $14 Ratty-Shack iron (something like This )should do the job okay. Don't try to use one of the big soldering guns ;D.

You'll need some solder, preferably a thin non-acid flux-core, and I prefer to have additional flux to tap the iron into occasionally. That may not be normal procedure, but it works for me, and keeps the iron well tinned.

Replacement caps you should be able to find on ebay or Digi-Key. I'd recommend buying from a good domestic seller if taking the ebay route.

I have cheated and successfully used caps close to the bad cap's rating, but that was only because I had them on-hand. Make sure to match capacitance -and- voltage rating. A 5V cap won't last long in a 30V world. Getting a cap a bit higher than the bad cap's voltage won't hurt (IIRC, that was one of the fixes for the original Airport base station - replace the overheated caps with ones that had a 5V higher rating).

The caps you'll be replacing are polarized, so it's important to get the + and - the right way round. Orientation should be marked on the board underneath the capacitor, or you could mark the '-' position with marker before removing the bad cap.

Read a few guides, work slowly, etc. and I hope cap replacement does the trick. It's a sweet feeling when you bring one back to life.

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MaxTek's picture
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Joined: Dec 20 2003
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Thanks for the info and the l

Thanks for the info and the link for the soldering iron. What do you think about these two webpages on this issue?

First one is on the iMac G5 repair
http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php

Second one (same guy) is in detail about the soldering technique
http://jimwarholic.com/2009/09/soldering-tips-for-lead-free-solder.php

Since the iMac came complete, I really want to fix it and do it right the first time.

MaxTek

eeun's picture
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Looks like you've found a bet

Looks like you've found a better reference than I found Smile

I haven't knowingly encountered lead-free boards yet, and all my solder is still heavy metal, so I really can't offer any opinions or advice on that subject.

One thing I could suggest is once you get your iron, find a scrap motherboard or two and get acquainted with de-soldering the caps. Cut your chops on some scrap before doing the real thing. Soldering irons on their own are not good at removing chips and multi-pin components, so stick to caps and anything with just one or two connectors.

I rock the capacitors out when I remove them. I heat one pin while applying pressure to one side of the cap from the opposite side of the board, then switch to the other pin. Work it out slowly, and don't pull too hard or you can pull up traces from the board.

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Joined: Dec 20 2003
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Re: Looks like you've found a bet

eeun wrote:

I rock the capacitors out when I remove them. I heat one pin while applying pressure to one side of the cap from the opposite side of the board, then switch to the other pin. Work it out slowly, and don't pull too hard or you can pull up traces from the board.

Just get two soldering pencils. The last time I checked, the 15watt grounded soldering pencil at Radio Shack was less than $10.

Apply one soldering pencil to each side of the cap and lift it off when you can do so without applying any significant force. Be patient. It's better to overheat it a little than it is to pry the cap off the board and tear a pad away with the cap.

While the one pencil side to side method is doable, it is also the largest single cause of lifted and torn component pads. The extra $10 is well worth it compared to trying to repair a lifted or torn pad on the circuit board.