Imac24 computer- won't boot up-

Mar 13, 2009

- Yes the computer started right up & is running with no issues-- as an added test there appears to be voltage display mini leds, (green) on the bottom center of the motherboard. (visible thru the bottom vent screen by the memory chip cover). looks like 3 light up when power is correct, I only had one light before changing the power supply.

Mar 15, 2009

- Here's a few suggestions: There appears to be a couple different power supplys in the imac 24's - my suspect model had 2 large aluminum heat sinks on the bottom & sticking out the side. The burned part was visible immidiatly on top of the board (surface mount transistor), examine the power supply components for damage, including any capacitors. A swelled silver top indicates a failed cap from overheat and will need replaced. Likewise I have repaired many motherboards with the swelled capacitor problem. Using a voltmeter, check for presence of +5, +12, +3.3 volts coming out of the power supply to the motherboard and/ or to the hard drive when the computer is turned on. I think there is an addtional +24v to the display.
http://en.wikipedia.org/wiki/Serial_ATA for power pinouts to the sata drive. Also a bad component may rob power- a non-running fan could be shorted, try unplugging anything that doesn't start--hard drive power- dvd power- fans- or display- (to test without the display listen to see if the hard drive spins up)