diagnostic led blinks once when ac is connected

The Imac emc 2389 won't boot. There is no chime no beeps and just a black screen. I bought this computer used and non-working. I was told the power supply was bad. I swapped the power supply and ram from a working mid 2011 emc 2428, no difference.

I removed the glass and screen to access the diagnostic lights. Number one diagnostic led blinks once when I connect the ac cord then goes out. When I push the power button it blinks once more then goes out. No other leds light up. Any suggestions. I do have a multimeter and know how to use it. Thank you in advance

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Some others with this behavior no LEDs lighting, replaced power supply. dead. AC line filter?. You could remove the HD and see if you can boot to an optical or external drive. Or, put the HD in an external case and test it on another (working) Mac.

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I removed the hard drive and optical drive and tried starting the computer. Same results. I also installed a working hard drive still have the no.1 blinking led.

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You need at least one boot drive. Since removing the drive did not change behavior I lean toward a PSU (power supply unit) problem.

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Working on power supplies is very dangerous for a DIYer. To get an idea (this is not the correct power supply-but an example) look here to see what's involved in testing the output voltage. You are working with mains power, and capacitors that store enough voltage to kill! Do not work alone.

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Are you any further forward with this issue? It points to a bad PSU but unfortunately at this stage you cannot rule out a problem with the logic board either.

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