Mid-2010 27" iMac Powers on, No Video, No Chime

[Jimmy-Chivas]

Hey old Mac heads. Looking for some help/advice with a troubled machine.

I've had 5 of 7 units go well during my refurbs/upgrades with 27" iMacs, so I know my way around these machines okay enough. However, this one has been kind of weird and I haven't quite seen this yet.

I did a complete tear down / cleaning / refurb, and tossed in a compatible I7-870 as an upgrade over the I5-760 it came with. Also replaced the CMOS battery with the exact same type of battery specific to Apple computers (in case you were wondering).

Before tear down the unit powered up and booted into Mac OS just fine.

Carefully put everything back together and the unit powers on but with no chime, no video, and fans are at full speed. Tried resetting PRAM a few times, but that didn't seem to matter. It appears that only the 1st diagnostic light is on all the time, which doesn't make sense. Wouldn't the 2nd one be on also?

Initially I figured maybe the i7 CPU from Ebay was bad, so I put the known-good I5 CPU back in, buttoned it up and tried again. Nope. Same exact problem.

Next, I removed the monitor, powered the unit on and was able to confirm that all three fans are working.

Tried resetting the PRAM again, but no luck. Tried one slot of RAM, same thing.

My guess is that the GPU has perhaps failed. I have another known-good Radeon HD 5750 1GB VRAM from a previous 27" 2010 iMac I could swap out. Does that sound like the next logical step? Or perhaps is there something else I should try first? Thank You!

 

[theMarble]

My guess is that the GPU has perhaps failed. I have another known-good Radeon HD 5750 1GB VRAM from a previous 27" 2010 iMac I could swap out. Does that sound like the next logical step?

Seems odd that the GPU would suddenly fail when it is put back together, as it was working before the teardown. I would try the other 5750 to see if that fixes anything.

I would also try putting the original CMOS battery back in. At this stage, there is no point testing and replacing hardware that worked before the teardown. Limit your testing to the parts that you replaced/upgraded at first.

 

[Jimmy-Chivas]

Seems odd that the GPU would suddenly fail when it is put back together, as it was working before the teardown. I would try the other 5750 to see if that fixes anything.

I would also try putting the original CMOS battery back in. At this stage, there is no point testing and replacing hardware that worked before the teardown. Limit your testing to the parts that you replaced/upgraded at first.

Works with the other 5750. Bummer to think the other GPU is dead. I guess it's not odd given how old these beasts are at this point. Anything can happen.

Wouldn't you know it, after finally getting this one to boot...and the left speaker is making a horrendous noise. Good thing I have a spare parts unit I can toss a speaker in there.

Hopefully I'm not chasing some other problems caused by some power issue or a failing power supply. Who knows. All bets are off with these dinosaurs I reckon.

Going to run some diags on this one as is and see if it dies. If so, perhaps could be the power supply. I have a few spares that have already been tested anyway.

 

[Nguyen Duc Hieu]

It's nice to know that only the GPU was bad.
I hope it would be the same with my iMac 2011. (Total death with only 1 diagnosis LED lit up)

 

[Jimmy-Chivas]

It's nice to know that only the GPU was bad.
I hope it would be the same with my iMac 2011. (Total death with only 1 diagnosis LED lit up)

Hopefully that just means the PSU is faulty and not the logic board. Good Luck with that!