Original post by: johnsawyercjs ,
Thomas, I don't know if you got this problem resolved yet, but in case you haven't, maybe this will help: I'm currently trying to diagnose an Intel-based iMac, Mid-2007 2.0 GHz model, which is currently playing the same symptoms as yours is/was--the same error beep sequence, kernel panics, runs sometimes, etc. I managed to get the Mac to run long enough to allow me to install a thorough memory testing utility called Memtest onto its hard drive, which you run in single-user mode at startup. It kept displaying RAM errors, even with known-good RAM boards, so I felt it was likely there was a problem with the RAM-controlling circuitry on the logic board. So, I ordered a replacement logic board. That didn't help. Swapping logic boards with the supplier requires that you first remove the CPU and GPU chips before sending the supposedly bad logic board to them, and installing these chips onto the replacement logic board, so the only remaining part from the Mac I'm working on, that's likely to be the cause of the problems, is the CPU chip (the GPU is unlikely, especially since in these earlier iMac models, it doesn't access the main RAM bank). If you haven't already spent money on this, I'd recommend trying a known-good CPU before you try a logic board--it's cheaper, and with these particular symptoms, more likely to be the CPU. Prior to working on this Mac, I'd never seen a bad CPU cause RAM errors, in 23 years of working on Macs. But the way statistics works, is that a number of other techs have probably seen this problem several times in fewer years, especially with some Intel iMac models, which I suspect were assembled with flaky processor chips that failed after a year or two.