Is my power supply faulty?

When I press the power button on my iMac it begins to start up, but halfway through the start chime it loses all power and needs to be unplugged before the power button can be pressed again. The screen always remains black.

First diagnostic LED is lit. Upon pressing power button second LED lights up, but halfway through the startup chime the third LED lights momentarily then the whole thing dies completely leaving no LED lights on until I unplug it and plug it back in.

iMac will boot up and run with the LCD completely disconnected, but not with it connected. When running LEDs 1-3 remain lit and I can see the iMac on the network and access it's shared folders ie. it appears to be running fine.

I found this link very helpful Is my LCD toast or is it my power supply?

but have got to the point where I am trying to figure out whether it is the power supply failing when the drain comes on from the backlight or the lcd that is causing the issue. The SMC and the PRAM have been reset and I have checked the ram modules and ruled that out (unless they happen to both be faulty).

The tech specs as provided by the everyman website provided no information on the PSU outputs but here is my serial number in case I'm doing it wrong 1784704tze4.

Having only a rudimentary knowledge of electronics my multimeter testing was as follows from the ribbon strip:

my reason for the pins selected for the common is based on this thread PSU providing enough voltage? for someone trying to work out a problem with the same power supply and as you will see they are vastly different.

The power supply is an OE Liteon PA-3241-02A1.

There does not appear to be any popped capacitors.

Below is the voltages I observed on the main power connector when the machine was in standby mode (LED 1 lit) with lcd disconnected, and in brackets with power on and 1-3 LED lit, lcd disconnected:

Pins 3-7 have continuity with earth pin on wall plug

• Pin #1 (closest to top of screen) Common

• Pin #2 0v

• Pin #3 0v

• Pin #4 0v

• Pin #5 0v

• Pin #6 0v

• Pin #7 0v

• Pin #8 +23.6v (+25.8v)

• Pin #9 +23.6v (+25.8v)

• Pin #10 +23.6v (+25.8v)

• Pin #11 +23.6 (+25.8v)

• Pin #12 +23.6 (+25.8v)

next

• Pin #1 (closest to top of screen) -23.6v (-25.9v)

• Pin #2 -23.6v (-25.9v)

• Pin #3 -23.8v (-25.9v)

• Pin #4 -23.8v (-25.9v)

• Pin #5 -23.8v (-25.9v)

• Pin #6 -23.8v (-25.9v)

• Pin #7 -23.8v (-25.9v)

• Pin #8 0v

• Pin #9 0v

• Pin #10 0v

• Pin #11 0v

• Pin #12 Common

next

• Pin #1 (closest to top of screen) 0v

• Pin #2 0v

• Pin #3 0v

• Pin #4 0v

• Pin #5 0v

• Pin #6 Common

• Pin #7 0v

• Pin #8 -23.8v (+25.8v)

• Pin #9 -23.8v (+25.8v)

• Pin #10 -23.8v (+25.8v)

• Pin #11 -23.8v (+25.8v)

• Pin #12 -23.8v (+25.8v)

next

• Pin #1 (closest to top of screen)

• Pin #2 0v

• Pin #3 0v

• Pin #4 0v

• Pin #5 0v

• Pin #6 0v

• Pin #7 Common

• Pin #8 +23.8v (+25.8v)

• Pin #9 +23.8v (+25.8v)

• Pin #10 +23.8v (+25.8v)

• Pin #11 +23.8v (+25.8v)

• Pin #12 +23.8v (+25.8v)

so there is probably a lot of irrelevant info there for someone who knows what they are doing sorry. Am I right in thinking that those are not healthy outputs and that the PSU is faulty?

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