Power Supply
Caution
There are high voltages present in power supplies when operating and these are stored in the capacitors on the PCB and remain even after the supply is turned off and disconnected from the AC mains supply. If you haven't worked on electronics previously then don't start here!One of the least desirable aspects of the ATX PSU spec is that of the lack of a front panel mains power switch. On my old P200 computer, the AT power mains switch on the front panel turned off the Auxiliary power outlet socket (sometimes called a monitor socket). I put an IEC plug on the cable end of a 4-way 13A socket strip so that when powered from the auxiliary socket, all my peripherals could be powered off on the same computer switch. These include the Printer, Scanner, Bass box and Stereo powered speakers. Another undesirable aspect is the lack of a mains switch at all. I decided to do something about this state of affairs.
This is a view of the mains input area of the 300 Watt power supply that came with my JNC case before any modifications had been done. The black item on the right is a fan and the mains in and auxiliary out connectors are at the left. These are wired directly in parallel and a pair of wires supplies the input filter on the PCB. Note there is a gap on the back panel between the connectors and the fan under the green/yellow earth wires.
That gap was just large enough to mount a miniature mains switching 12vdc coil relay with double-sided mounting tape. Its contact set is double pole change-over and I paralleled them to increase their rating to 10 Amps. The coil is wired back to the +12VDC output pads. Thus when the shut-down process tells the power supply to go to sleep, the +12Vdc supply is turned off and the relay drops out and switches off the mains to the auxiliary connector and hence all the peripherals.
Although the chassis of the power supply was equipped with a voltage selector cut-out between the two mains connectors, it wasn't fitted with a voltage selector switch. So I fitted a miniature toggle switch there and wired it in series between the mains inlet and the other mains items.
Also visible on the back panel is the fan grill which has since been removed and a wire guard fitted about 6mm further away. This reduces the turbulance of the exhaust air stream and leads to quieter operation.
