Bench PSU Repair Help please

[Aerobyrd93]

Hi,
So my uncle has (had?) a power supply, which is quite similar to this one http://www.ebay.com/itm/Mastech-HY5003-2-300-Watt-Digital-Benchtop-Power-Supply50VDC-3A-Dual-Output-/121675579358?hash=item1c546dffde:g:qLEAAOSwpdpVefgD

That is, until I tried the incorrect way to try and use it as a +/- supply to power a +/-15v op amp (I'm sure there's a way to do this, but I still don't know for sure how). I shorted the +side of one channel to the - side of the other, then pressed only the right button (there are two buttons on the front controlling whether the supplies are in series/parallel. The diagram on the front indicates press only the left to put the sides in series, but for some reason I pushed only the right.) Pop, Fizz, Smoke, Smell    .

The fallout is thus: If you turn the power supply on currently, the left side appears to be working just fine with no damage, while the right side is stuck at 49.9v (on a 30v unit) This causes several resistors to quickly heat up and begin to smoke, making it hard to test the system better while it is on. If anyone can provide a possible solution, it would be greatly appreciated. I've offered to buy him a new one if I can't repair it, but I REALLY don't want to do that.
 

[voltz]

Hi,
Have you located a schematic for the PSU yet? if not, that would be the first step.

"while the right side is stuck at 49.9v (on a 30v unit) "

This sounds like output transistors E-C shorting. You are seeing the full supply voltage, none regulated, at the output terminals. Check those. ( usually something like 2n3055's or 2n3773's etc).. If not, then go further back to the regulator circuit itself.
Presumably, the PSU has no 'crow bar' protection to clamp over voltage.

Hope that helps.

[Aerobyrd93]

Thank you, I will try and take a look at those transistors. Unfortunately, I have not had any luck whatsoever finding a schematic as of yet. It's kind of a generic Ebay power supply, and even the name doesn't yield much in the way of useful results. It's an Arksen 305-2d.

[voltz]

You're welcome.

This thread talks about the 305-D single version:
https://www.eevblog.com/forum/reviews/beware-yihua-yh-305d-bench-psu/

Might help.

Its common for a single device to be released under many brand names. Its a case of working out what is really is and then getting the diagram.