16-11-2017, 12:06 PM
That supply will be running at upwards of 50kHz.
If it's a flyback type, the voltage at the collector of the switching transistor can reach many hundreds of volts when it turns off. Enough to damage many a multimeter, especially when you consider that is a very narrow spike with lots of HF energy.
Most ATX power supplies are bridge types, so the switching voltage is constrained to the unregulated DC input voltage (325V). Still not a job for a multimeter though.
Isolation transformer, high voltage divider probes, oscilloscope.
All that said, most faults are capacitors or start-up problems. Anything more involved than this is simply not worth investigating, as ATX PSUs are so cheap to replace (£20 or less!).
And when on the bench, another trap is to forget to include a load on the output - this causes the main rail to fire its crowbar, shutting down the PSU with a whine.
Don't forget that an ATX PSU has two separate power supplies within. And the main supply won't come to life unless you short pin 16 to ground.
The standby PSU is usually a flyback type. This needs to be working - if not, the main PSU won't ever come up.
For power-supply geeks like me, this site is a joy: http://danyk.cz/s_atx_en.html - there are a whole load of PC power supply schematics on there, and while it's unlikely that the exact model in question will be covered, it's still interesting to look at the range of circuit techniques used.
If it's a flyback type, the voltage at the collector of the switching transistor can reach many hundreds of volts when it turns off. Enough to damage many a multimeter, especially when you consider that is a very narrow spike with lots of HF energy.
Most ATX power supplies are bridge types, so the switching voltage is constrained to the unregulated DC input voltage (325V). Still not a job for a multimeter though.
Isolation transformer, high voltage divider probes, oscilloscope.
All that said, most faults are capacitors or start-up problems. Anything more involved than this is simply not worth investigating, as ATX PSUs are so cheap to replace (£20 or less!).
And when on the bench, another trap is to forget to include a load on the output - this causes the main rail to fire its crowbar, shutting down the PSU with a whine.
Don't forget that an ATX PSU has two separate power supplies within. And the main supply won't come to life unless you short pin 16 to ground.
The standby PSU is usually a flyback type. This needs to be working - if not, the main PSU won't ever come up.
For power-supply geeks like me, this site is a joy: http://danyk.cz/s_atx_en.html - there are a whole load of PC power supply schematics on there, and while it's unlikely that the exact model in question will be covered, it's still interesting to look at the range of circuit techniques used.