i've got a pretty rare motherboard that i'm evaluating for repair. it's a biostar m7mia-raid which is the only ddr socket a motherboard ever produced, consumer or industrial, with an isa slot. its 20 years old now and finally gave up the ghost last month. i was saving a dd image of the hdd to a portable usb drive when i found it unresponsive with a black screen and a solid lit hdd led. after forcing it to power down it never posted again. the psu/cpu/case fans will spin and the onboard motherboard power led will light up, but no beeps or error codes even with the cmos reset and ram plus all expansion cards removed.
given the age, bad capacitors would seem to be the likely culprit, although their exterior appearance is absolutely pristine and the board never experienced any instability prior to dying so it's not a slam dunk. what concerns me more is that the motherboard was hooked up to a faulty power supply for more than a decade. the psu in question is an expensive clever power 500w unit that probably weighs more than 3 of those junk psu jobbies put together. it remains functional to this day and as far as i can tell with a multimeter on my testbed all the rails are still fairly close to spec under load.
the problem with the psu is that when the system is off it leaks voltage on the 12v and 5v rails. i measure around 1.8v on the 5v; 4v on the 12v wires when powered down. this only ever came to my attention when i happened to have the side panel off while swapping out components and noticed the case fans were still very slowly spinning (onboard motherboard led was also lit up when it should be dark). i'm assuming this could have been the condition of the pc for years (maybe even over a decade). after i caught the issue the motherboard persevered on for maybe another year with infrequent use before dying. every component from it, except ram, made it into a replacement kt133a sdram system and seems to be perfectly functional so nothing else got taken out with the motherboard.
my question is what kind of impact could this prolonged exposure to leaking voltage have had on system components? what electronics would be susceptible or immune? would there be any visible evidence to look for? hell, was it good, bad or indifferent to the capacitors?
given the age, bad capacitors would seem to be the likely culprit, although their exterior appearance is absolutely pristine and the board never experienced any instability prior to dying so it's not a slam dunk. what concerns me more is that the motherboard was hooked up to a faulty power supply for more than a decade. the psu in question is an expensive clever power 500w unit that probably weighs more than 3 of those junk psu jobbies put together. it remains functional to this day and as far as i can tell with a multimeter on my testbed all the rails are still fairly close to spec under load.
the problem with the psu is that when the system is off it leaks voltage on the 12v and 5v rails. i measure around 1.8v on the 5v; 4v on the 12v wires when powered down. this only ever came to my attention when i happened to have the side panel off while swapping out components and noticed the case fans were still very slowly spinning (onboard motherboard led was also lit up when it should be dark). i'm assuming this could have been the condition of the pc for years (maybe even over a decade). after i caught the issue the motherboard persevered on for maybe another year with infrequent use before dying. every component from it, except ram, made it into a replacement kt133a sdram system and seems to be perfectly functional so nothing else got taken out with the motherboard.
my question is what kind of impact could this prolonged exposure to leaking voltage have had on system components? what electronics would be susceptible or immune? would there be any visible evidence to look for? hell, was it good, bad or indifferent to the capacitors?
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