Strange Issue. Logic Board? PRAM battery? NVRAM?

[SuperCooper]

Hi. This is my first post here. I have a 2nd Gen. iMac G5 (Ambient Light Sensor). It froze yesterday, and the fan was revving up...so I turned it off. When I turned it back on the screen was blank, and the fan started running hard again. I reset the PRAM, and it came on again. Everything worked fine for a few minutes, but it soon froze again. I restarted it, and the screen was blank again. I repeated the PRAM reset, and it worked for a little while...but soon did the same thing. (When I reset the PRAM, I can turn it off then turn it back on and it still works...until it freezes again.) I took the back off to check diagnostic LEDs.(Without a PRAM reset) The first two lights came on, but the logic board light didn't come on. I reset the PRAM, and the 3rd light (Logic Board) came on. So, somehow when the Mac freezes, it's preventing the logic board from communicating with the LCD...until the PRAM is reset. I'm not sure what to think. Could this kind of thing be caused by a bad PRAM battery? Is there anything else I can try? I haven't reset the NVRAM yet. I'd appreciate any input. Thank you. -Seth

 

[DeltaMac]

Try an SMU reset:
Resetting the SMU (System Management Unit)
1. Unplug all cables from the computer, including the power cord.
2. Wait 10 seconds.
3. Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
4. Let go of the power button.
5. Press the power button once more to start up your iMac G5.

If that doesn't help your problem, then your logic board may need replacing.