i have a power supply with issue in -12v rail. after 15seconds of power the diagnostic begins beep and shows LL ON -12V which means undelvoltage .. i have replaced the most of the capacitors due to missing capacitance (checked with capacitometer)..but i have stil the same problem . can anyone help me to find the solution to fix it....the diodes are ok...i have checked..
iso p500-spp 400 watt power supply cpu issue
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Re: iso p500-spp 400 watt power supply cpu issue
maybe the diode.
diodes can look o.k. on a meter and then fail as they warm up in circuit.
only 2 ways to detect that.
1: blast it with compressed air or freezer spray while running to see if it fixes the problem.
2: meter both the ac input and the dc output to see if the input drops when the output does. -
Re: iso p500-spp 400 watt power supply cpu issue
maybe the diode.
diodes can look o.k. on a meter and then fail as they warm up in circuit.
only 2 ways to detect that.
1: blast it with compressed air or freezer spray while running to see if it fixes the problem.
2: meter both the ac input and the dc output to see if the input drops when the output does.Comment
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Re: iso p500-spp 400 watt power supply cpu issue
I've seen those "testers" mis-report a lot of power supplies as being bad. The problem is they don't put a significant load on the output of the PSU. Therefore, the -12V rail will almost always show low voltage. On group-regulated PSUs, other rails may appear low too. For more accurate results, add a load to the PSU - preferably at least 1-2 Amps of current draw from the 3.3V, 5V, and 12V rails each. That should bring the -12V rail to a more normal value.
So for the above, I suggest connecting the PSU to a crappy motherboard (something like an old useless Pentium 4 or similar board), turn on the motherboard, and then measure the voltages with a multimeter at the ATX connector. I bet you the -12V will be OK then.
Also, since you mention this is an "ISO" -branded power supply, you may want to post some pictures here. Some of them are built well and worth recapping, like this one:
https://www.badcaps.net/forum/showthread.php?t=46636
But some cheap variants of the ISO line can be total crap and very gutless. Here's is a gutless one that probably will need a ton of modifying if meant to be used with a PC again:
https://www.badcaps.net/forum/showthread.php?t=39370Last edited by momaka; 02-15-2021, 12:44 AM.Comment
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