Mastec HY3005 not working

[danlab]

I have a Mastech HY3005 power supply that died about two years ago and I'm finally getting around to try to fix it.

When I power up the unit, the voltage display will show between 0 and 1.4 volts (as I move the adjustment knobs) while the Amperage display shows 0. I have tried putting a load on it (10 ohm 10 watt resistor) with no effect. I also checked with a multimeter and the outputs do not show any voltage.

The supply hasn't been modified at all. I did open the case to look for obviously damaged parts, traces, or loose wires and didn't find any.

Anyone else have similar problems, or ideas on how to fix it, I would really rather not buy a new supply If I don't have to.

[smason]

Re: Mastec HY3005 not working

You can get a schematic here:

http://service-manuals.info/meters/p..._hy_10209.html

[jcotton]

Re: Mastec HY3005 not working

I just fixed a friends' HY3005-2.

Shorted 2n3055, no heat sink grease, just thermal pads contaminated at install with dirt.

Shorted 6a10 diode, open trace between diode bridge and relay section.

The previous technician that worked on the unit fitted a 2x larger than rated fuse and
popped the trace.

If someone has used the supply to charge model car/airplane battery packs the
protection diode on the front panel likes to short... (per other web forums)