psu from a 2000 system and the fuse keeps blowing not sure why
Albert
The usual cause for this is at least one of the four diodes on the AC input bridge rectifier has gone short circuit. They'll often be 400V diodes, which is fine for 230V mains (AC peak is +/- 325V), but voltage spikes in excess of 400V can cause sudden failure.
And sometimes the high voltage DC switching transistor (there will be one or a pair of them on a heat sink) may have gone short circuit, and in the process this can also damage the input bridge rectifier due to the high fault current that flows at power on before the fuse blows.
It's pretty much the same fault finding process for most switch mode power supplies. I wrote
this guide on A3000 power supply repairs - see the bottom of the page.
