Chosen Solution
I tried SMC reset, opened up the 2011 21.5” iMac, reconnected the power cables. I only see LED #1 turned on that indicates power. I reseated the CPU as well and even replaced the CMOS battery. Doesn’t turn on - No fans spinning, no chimes / sounds and no display. What could the issue be? How do I find out what’s gone wrong? A few questions: Could a bad GPU prevent it from turning on?Could a bad CPU be the issue?Will it turn on without HDD?How do I test the power supply unit and will the diagnostic led turn on in case of bad power supply?Could it be the Logic Board? PLEASE REPLY AS SOON AS POSSIBLE Thanks, BTW Update (02/11/2021) @danj When I disassembled the mac’s gpu, I found that the thermal paste leaked onto the chip. The heat sink is black on top. Is this normal? Images:
https://drive.google.com/file/d/1GL0dzU_… ??????? https://drive.google.com/file/d/1Furfhe8…
There are two directions here and I can’t tell you which way to go. 1 - The power supply or logic has failed 2 - The GPU board has shorted out At this point you need to test the logic board voltages. You’ll need to get the schematics and boardview drawings for your system so you can check the voltages.
Well you’ve got some work here! You’ll need to carefully clean off all of the old TIM being careful not to pull off the tiny SMD devices also on the chip carrier. I would use a Rechargable spray can loaded with 85% or better isopropyl alcohol] Using the snorkel you can dig out the TIM that gets under the SMD devices (a strong portable shorting issue)! You’ll need to get some fresh TIM onto the the raw GPU silicon chip without going over the edge. It doesn’t take much as you can see the provious application was way too much! The four VRAM chips will need new thermal pads as well. You really don’t want the gapping TIM (white thicker paste) as its just not very good. Carefully dry fit the heatsink and using a feeler gage or some thin strips of card stock measure the distance between the VRAM and the heatsink so you get the proper fit. Here is what I would use: Thermal Grizzly - KRYONAUTThermal Grizzly - Minus Pad
