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nkear5 01-28-2011 07:20 AM

iMac G4 20" (USB 2.0) will not turn on
 
I recently purchased a non-working 20" iMac G4. The seller described the iMac as having a problem related to the logic board.

I re-assembled the iMac and plugged it in to see the problem for myself. After resetting the PMU, if I pressed the power button, the fan in the base would turn on. Nothing else happened. After a few minutes the fan would not power on either. If I put my ear near the screen or base, I can hear a faint, high-pitched electrical whine, which should indicate that power is being supplied to the computer.

Would you agree with the seller that the problem is likely to do with the logic board, or can you think of another problem? Would replacing the PRAM battery do any good? I am prepared to purchase a new logic board or power supply and am capable of installing it myself.

Thanks.

pigoo3 01-28-2011 07:29 AM

Quote:

Originally Posted by nkear5 (Post 1176751)

Would you agree with the seller that the problem is likely to do with the logic board, or can you think of another problem? Would replacing the PRAM battery do any good? I am prepared to purchase a new logic board or power supply and am capable of installing it myself.

Yes it most likely is the logic board or PS. If it's broke it's broke.:(

As far as a new logic board or PS...unless you can find them at a very low price or if the cost is not a problem...then go for it. But depending on the model iMac G4 you have...in it's present condition...it may be worth $50 bucks (for parts)...maybe less. In 100% working condition it's only worth around $100-$125.

I'm pretty sure a logic board will cost more than that...and power supplies are expensive as well for such an unusually shaped computer.

Good luck,

- Nick

nkear5 01-28-2011 07:42 AM

The 20" model usually fetches quite a bit more due to its rarity, but in this case, I am looking to fix it for personal use, not re-sale. I found prices for either part before I purchased the computer. The trouble is determining which one to replace.

pigoo3 01-28-2011 07:58 AM

Quote:

Originally Posted by nkear5 (Post 1176758)
The 20" model usually fetches quite a bit more due to its rarity, but in this case, I am looking to fix it for personal use, not re-sale. I found prices for either part before I purchased the computer. The trouble is determining which one to replace.

Yeah...the 20" models are less common. Hopefully you found a good source for reasonably priced replacement parts. If it were me...trying to choose between a bad logic board or a bad power supply...I would go with the bad power supply.

Power supplies are more likely to go bad than a logic board assuming:

- no one spilled liquid on the computer
- no heat or cooling related issues
- or there were no electrical problems/surges that the computer was exposed to in it's former life/lives.

I'm assuming you've checked the logic board for any "burn-marks" indicating any possible issues.

Good luck,

- Nick

MacMan886 01-28-2011 08:37 AM

Does anyone know if the G4 iMacs have the same capacitor problem as the later G5 iMacs? If they do, I recommend that you pull apart the iMac to see if there are any swollen/leaking caps on the logic board or on the power supply.

If there are any, replace them with brand name ones that match the specs on the side of them....if you don't know how to solder, take the board or power supply to a TV repair shop, and they will be glad to replace them at a small cost.

I've replaced caps before on computers that wouldn't turn on, locked up frequently, had video problems, etc. and it fixed them.

However this may not be your case... you just might have a bad logic board or power supply in general.

pigoo3 01-28-2011 08:40 AM

Quote:

Originally Posted by MacMan886 (Post 1176774)
Does anyone know if the G4 iMacs have the same capacitor problem as the later G5 iMacs?

Not as far as I know. Some model G5 iMacs & some eMacs were the computers mostly affected by the capacitor problem.

- Nick

nkear5 01-28-2011 08:53 AM

Quote:

Originally Posted by MacMan886 (Post 1176774)
Does anyone know if the G4 iMacs have the same capacitor problem as the later G5 iMacs? If they do, I recommend that you pull apart the iMac to see if there are any swollen/leaking caps on the logic board or on the power supply.

If there are any, replace them with brand name ones that match the specs on the side of them....if you don't know how to solder, take the board or power supply to a TV repair shop, and they will be glad to replace them at a small cost.

I've replaced caps before on computers that wouldn't turn on, locked up frequently, had video problems, etc. and it fixed them.

However this may not be your case... you just might have a bad logic board or power supply in general.

I had to assemble the iMac myself, so I did check the logic board while I had it out. All the capacitors are solid capacitors and there are no signs of damage to them.

MacMan886 01-28-2011 09:14 AM

Ahh, then you are probably looking at a logic board or power supply failure. I don't have enough knowledge on the flat panel iMacs to tell you how to test the power supply or anything. Hopefully someone can help you out.

All I do know is that there is quite a few of these iMacs on eBay that have the same symptoms, so it seems to be a common problem.


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