First post, by justin1985
I just got a BCM IN5598 / Packard Bell 850 micro ATX motherboard from eBay. It was described as having been working before it was put away for several years, and arrived looking absolutely perfect - clean, no sign of any damaged components, and no signs of any scratches and in an anti-static bag. It came with 4 x SIMMs and a Cyrix MII already fitted.
I loosely fitted it to a case (3 or 4 screws) and tried powering it up with a modern ATX PSU (which I'd tested with a PSU tester). Initially there was nothing apart from the CPU and PSU fans spinning up and the keyboard LEDs flashing, but then the CPU fan spun back down, but the PSU fan stayed on.
I tested the coin cell battery, which was dead, replaced it, and sure enough it booted! I power cycled it a few times, saving the date time etc., powered down and added a mouse and floppy drive, and successfully booted DOS. Then I powered it down, and noticed the PSU fan was still on for long enough to realise it wasn't just cooling down. I powered it off at the wall, tried again, but then it went back to just spinning up the CPU fan then back down, with keyboard LEDs flashing but no POST beeps.
After a minute or two, I noticed an electrical crackle sound (that actually kind of seemed to come from the wall socket rather than the PSU or motherboard!) Obviously yanked the mains cord from the wall within seconds. I briefly wondered if maybe something had been shorting against the case, but checked carefully and that seems really unlikely (foam spacer blocks between many of the mounting holes and no mounting spacers in wrong places). I moved it out to the open workbench now.
Since then I've tried testing the PSU again, swapping to the oldest ATX PSU I have (P4 era), removing the battery for a few minutes to reset the CMOS, and giving the SIMM slots some contact cleaner + cleaning the SIMM contacts with an eraser. Still the same behaviour - CPU fan spins up, keyboard lights flash, CPU fan spins back down, PSU fan stays on. In fact, most recently the PSU has powered up and the CPU fan spun up immediately on connecting to the mains - which it didn't do before.
It feels like maybe something related to voltage regulation was intermittent, but has now failed? Any ideas where to start?