iMac Not Turning On - No Diagnostic LED's Lighting

#1

Hi All,

Longtime reader of the site, but new to the forum and was hoping someone may be able to provide some advice.

I have a 2016 27" iMac - A1419

• 4.0GHz quad-core Intel Core i7, Turbo Boost up to 4.2GHz

• 8GB 1867MHz DDR3 SDRAM - two 4GB

• 1TB Fusion Drive

I went to turn it on the other day and it would not start, no activity, no chime. I did a reset and, still nothing. I unplugged the power cable and put it in a different point. It started up and I was able to login and get working, but within 1 minuted, it shut down again and would not restart.

I removed the power cable, waited 30 seconds and plugged it back in. It started again, but instantly shut down. I went through this process several times, with similar results.

Eventually, it would not start, but I could hear the fan going.

The next day, there was no fan noise, nothing happening, not matter what combination I tried.

For reference, I had also done the SMC and PRAM resets.

I ordered some screen tape, so I could remove the screen and check the LED's. 

I have removed the screen and plugged the cable into a socket, tried every combination of powering on methods and not one of the LED's lights up and there is no fan noise.

Any ideas, whether I will be luck enough for this to be just a power supply, or does this indicate a logic board failure?

Thanks in advance for any and all help.