Hello
This is a quick teardown and fix of a Chinese variable power supply.
While trying to measure a negative power supply I’ve discovered that the negative terminal was shorted to main’s earth and case
The construction is very dubious: the entire front piece is made of plastic with some sort of metal inserts,
The display section and regulator boards are OK, nothing too cheap. The regulator is based around a LM324 quad op-amp. There are some 78XX / 79XX regulators with heat-sinks make out of aluminium profile. The PCB’s are single sided with a lot of flux residue but they don’t look hand soldered.
It uses two power devices mounted on a tiny heat-sink and a huge noisy fan.
The output posts are the worst I’ve ever seen: the nuts are already rusted and the inserts are badly machined.
Across the earth post and the negative terminal the manufacturer inserted a small 100nF, 63V capacitor that failed shorted. There is also a reverse protection diode across GND and VCC outputs.
After removing the shorted cap. the fault was removed