Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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LED driver board smoked - but why?

Hi all,

My daughter's 2009 iMac lost its display over the weekend, along with a burning smell. When I opened the case (much easier than I expected) I found that the LED driver board had a couple of cooked components - the middle one of the three large transistors on the underside (Q2 in the image located at and the large inductor next to it looked brown as well (L2 in that image) as well as the diode SD2 on the other side. So clearly those devices are part of a power supply circuit which was trying to supply more than its rated current and failed.

My question is, if I replace this board with a new one, is it likely to fail as well? As in, did it happen because of a short somewhere else? There doesn't seem to be other damage but I do know the front of the computer was wiped down with a damp cloth earlier in the day. It was working for at least an hour after that, but still.

If anyone knows the setup of these machines well, could you suggest where to look for possible problems? Or should I just replace the board and cross my fingers?

Thanks for any advice,


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Matthew Kirkcaldie, sounds like a short limited to the LED driver board. I would only replace that one.

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Thanks for the reality check! No liquid mark on the board, but who knows. Anyway, I will have a careful look over everything before putting it in. Is it OK to power up the machine with the case open so I can keep an eye on the replacement board?


that should be fine.


Thanks again - part arrives later in the week so I will report on how it goes.


Sounds good and keep us informed.


Replacement board went in without a hitch and didn't blow out when I fired it up. These machines are so nice to work on compared to the previous gen white iMacs. Thanks for your help oldturkey03.


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Matthew Kirkcaldie will be eternally grateful.
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