Don't, without deliberate testing, discount the rôle of the Mac's mains cable in all this. I have had a Snow 500 iMac since new. It has now been always-on since about 1983 but for a RAM upgrade and a new battery. Its MLB failed within three weeks, but since its replacement under warranty the only failure has been obdurate KP-ing a couple of months ago. 'Only' but for an episode of three or four weeks several years ago, while the iMac was still used in OS 9.1, in which it would 'fizz' once and black out, but reboot after a few minutes. Pure accident—unplugging and replugging the original rainbow mains cable—showed that the silicone cladding of the cable was allowing the connectors inside the female end of the cable to lose contact enough to arc over to the Mac's mains-input socket.
I let the Mac rest after the recent KP episodes because there were other things to do. It was now an OS 9.2.2/10.2.8 machine. I redistributed RAM between several iMacs, including the Snow, to give them 640MB each. Almost idly I tried to boot the Snow, and voilà! Back to its old self, as which it has remained now for four-or-so weeks.
I anticipated similar behaviour when my blue 17" CRT Studio Display began erratically fizzing recently. The display shrank and expanded with each fizz, but never blanked. Despite the marque's reputation for FBT failure I persisted to use it. Sometimes it was entirely trouble-free, and on other occasions I switched it off because the fault was persistent after about 10min. of use. Usually, but not always, firming the mains cable in the male socket delayed or prevented the onset of trouble. So I cannot yet be definite about the display's problem, but I don't discount the power input.
Finally, as reported elsewhere in these threads, a recently-acquired Plus 1MB was converted from a garbled-screen hulk into a working Mac by replacing the mains cable. In all of these anecdotal occurrences (I haven't physically tested any of the suspect cables) my impression was that the mains cable's IEC-C13 plug had slid into the Mac's socket rather too easily, which could equate with loose fitting between plug and socket contacts. It's worth your while to eliminate that as the cause of your problems, if only because it is a sneaky and unanticipated failure.
de
I let the Mac rest after the recent KP episodes because there were other things to do. It was now an OS 9.2.2/10.2.8 machine. I redistributed RAM between several iMacs, including the Snow, to give them 640MB each. Almost idly I tried to boot the Snow, and voilà! Back to its old self, as which it has remained now for four-or-so weeks.
I anticipated similar behaviour when my blue 17" CRT Studio Display began erratically fizzing recently. The display shrank and expanded with each fizz, but never blanked. Despite the marque's reputation for FBT failure I persisted to use it. Sometimes it was entirely trouble-free, and on other occasions I switched it off because the fault was persistent after about 10min. of use. Usually, but not always, firming the mains cable in the male socket delayed or prevented the onset of trouble. So I cannot yet be definite about the display's problem, but I don't discount the power input.
Finally, as reported elsewhere in these threads, a recently-acquired Plus 1MB was converted from a garbled-screen hulk into a working Mac by replacing the mains cable. In all of these anecdotal occurrences (I haven't physically tested any of the suspect cables) my impression was that the mains cable's IEC-C13 plug had slid into the Mac's socket rather too easily, which could equate with loose fitting between plug and socket contacts. It's worth your while to eliminate that as the cause of your problems, if only because it is a sneaky and unanticipated failure.
de