Pace PRD series power supply problems.
First thing is to check if the fuse has blown and if the transistor is S/C, if not the fault may be quite simple. If the fuse and transistor are OK, it's probably just 3 capacitors that need replacing - C5, C7, and C8, replace them with 105 degree versions as listed below. These also sometimes cause a high-pitched whistling noise from the PSU, and when it's dead may make a faint 'ticking noise.
If the fuse and transistor are blown then the best idea is to obtain a PSU repair kit. This provides modified component values to help prevent further trouble.
|FS1||1 Amp A/S, now 1 Amp Quickblow.|
|R1||was 4.7 Ohm, now 10 Ohm 3 Watt.|
|R8||was 0.75 Ohm, now 1 Ohm 1 Watt.|
|R14||100 Ohm 0.25 Watt non-flammable.|
|D11||3.9 Volt Zener|
|C8||10 microfarad 25 volt, now high-temperature.|
|C7||10 microfarad 25 volt, now high-temperature.|
|C5||4.7 micofarad 25 volt, now 22 microfarad high-temperature.|
I think these are all the parts supplied in the basic Pace kits, depending where you buy them you may get some have extra parts.
|D1, D2, D3, D4||Bridge rectifier, any may be S/C.|
|C2||47 microfarad 400 volt, may be O/C or S/C.|
|T2||Mains transformer, may be O/C or S/C between windings.|
UPDATE: April 1997.
Recently the original PACE kits have been upgraded, and extra parts have been added.
|R6.||was 15 ohm, now 8.2 ohm.|
|R15.||was 68 ohm, now 33 ohm.|
|C2||47uF 400 volt, now supplied in kit.|
When replacing the PSU components be very gentle with the PCB tracks, it is advisable NOT to use a pump action desoldering tool - use desoldering braid instead, a pump action tool can easily damage the thin PCB tracks.
One point to bear in mind, the primary side of the transformer is NOT isolated from the mains. This means you cannot measure voltage readings with the meter lead clipped to the chassis - you need to use the negative end of C2. Please be careful, all this side of the transformer is LIVE TO THE MAINS and you could get a nasty shock (I've had LOADS! over the years).
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