A1174 Intel Core 2 Duo 2.0GHz 20" iMac 2007
Following a year of non-use, worked fine. Then after several uses, intermittent refusal to boot. Sometimes would, sometimes as stubborn as a mule. Unplug 15s, replug wait 5s. Sometimes Y, sometimes N. Then one occasion power went during operation. No life. Taken apart (1st class honours in electronics, admittedly 23 years ago, but did remember anti-stat wrist strap) changed CR2032, looked for blown caps, checked PSU input and output voltages, including bridge rectifier - all good. Reassembled, started immediately. Next day, dead as a dodo. Suspect main logic board rather than PSU, but what do I know? About this fine beast, I know that I know too little.
A friend of mine wants to buy it, but I've explained it is faulty and I'm unsure if it is economically repairable. Short of sending it for out-of-warrantee repair, what fixes should I try and what can I do to be sure of my fix?