21.5 Imac 2011 random reboots

[Zeerocool]

Hello, I'm new to the forum. Sew at New to macs. I purchased my first Mac about 2 years ago and have been slowly swapping all my PCs. Generally I but broken macs on eBay and fix them. I have done this successfully twice before On macbook for my kids. This is a 2011 21.5 imac 2.8 i5 12,1. The previous owner said the hard drive crashed and he paid apple to replace it. Then about 4 months later it crashed again with Apple saying they didn't know what was wrong and they would start with the the video card and then mother board. He decided not to put the money into it. I paid $100 for it.

I started with the basics like running hardware check, swap hard drive, trying to do multiple ways of recovery with everytime the same result. At some point during the recovery the computer just suddenly shuts off and reboots.

Next a replaced the video card. Same result.

I'm planning on doing the power supply next as that's a cheap part swap. I just ordered one on eBay for $19. After that I guess it would be the mobo. That would depend on the cost I have into it at that point. Parting it out maybe the way to go if it gets to that.

Anyway just wondering if anyone has any suggestions I haven't tried.

Thanks.

 

[pigoo3]

Sounds like what you're experiencing are kernel panics (random lockups or reboots). Many times kernel panics are bad hardware based...and many times it's due to bad RAM. But...if you're purchasing these computers via eBay (with existing issues)...it's very difficult to guess at what the problem can be (since neither you or us have an exact history of the computer). And if it turns out to be the logic board (which it very well could)...replacement logic boards are usually cost prohibitive (unless you get lucky).

- Nick