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Apple Desktops Discussion of Apple's desktop machines including Mac Pro, iMac, Power Mac, and mini

Black Screen, Loud Fans, No 3rd Led, Help!?


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paulyd04

 
Member Since: Oct 03, 2011
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I bought a second hand mac from an older guy that wasn't working when I bought it. I thought being fairly handy with computers I might give it a go- it was a very cheap buy and as a last resort I believe I can part it out and still make money.

The iMac is a 2.33 20" Intel Core 2 Duo Machine. When I bought it, I plugged it in and all that would happen when you powered it on was the white light would come on, the fans would immediately turn on full blast, and that was it- fully black screen and no startup chime. Here's what I've done so far...

1. Resetting SMU by unplugging and plugging back in- no luck

2. Replacing the RAM with brand new ram- no luck.

So after that I took the lcd off to gain access and noticed the PRAM battery holder on the logic board was broken- a battery was loosely taped in with electrical tape. So I went out and bought a brand new battery and tried to boot the computer while holding the battery in place with my finger. Still the same thing happens- no 3rd led and immediately loud fans...

I've been doing alot of research and it seems like I might have a bad logic board but I hate to just give up at this point. I've now removed the harddrive and I was going to put it in an enclosure and see if it boots.

What else should I do? It is fully out of warranty (5 year old machine). Are there some other trouble shooting steps before I just part it out?

Some people say it might be a bad power supply but the first 2 leds come on fine and the fans spin very fast so the computer is getting power. I really need this computer to work as I planned on giving it to my wife for her to do work on.

Thanks!
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chscag

 
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Quote:
I've been doing alot of research and it seems like I might have a bad logic board but I hate to just give up at this point. I've now removed the harddrive and I was going to put it in an enclosure and see if it boots.
You've done some good research. The symptom you're describing is typical of a bad logic board. Since logic boards (even refurbished ones) are rather expensive, it may not pay to go any further in your repairs. Keep an eye open for a like machine that's not working and being sold for parts. Maybe you can pick up another where the logic board is still functioning.
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Head_Unit

 
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It could indeed be a bad logic board. However, I had a G5 with exactly that symptom and a new power supply fixed it. PS was turning the machine on, but not really enough power so I guess that perturbed the logic board or something.

Core 2 Duos sell around $400+ on eBay currently.

Power supply FOR A G5 was like $100-150; not sure about the logic board or PS for yours.

Take the thing to a good shop by you for diagnosis. You've pretty much done what you can do.
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paulyd04

 
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Hey guys... since i'm new here I can't post in the buy/sell/trade forum but wanted you all to know that I think I've isolated the problem to the logic board and so I've decided to part the computer out- have all kinds of stuff for sale- just message me if interested
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