Electronics > Repair
Mastech HY5020E 50v 20a Bench Supply: Economical to repair?
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richfiles:
Just a dump of pictures. If you need any details enhanced, let me know.

Thing was covered in flux like some cheap Chinese junk yet had Nippon Chemicon caps. There were actually a few solder balls stuck down in flux. Really should have been cleaned, especially if they are gonna splurge for good caps! ??? There's some smears cause I took a little isopropyl alcohol to a spot. Decided to deal with it later though. I didn't have time for more than the pictures today. There are two smaller module PC boards that plug in, but both are double sided boards using SMD parts. I can get more pics later.

A few pads are lifted, near the parts that blew, and in one spot where they soldered current handling wire onto the traces to beef them up. There is little to no charring on the solder side. I should have no trouble cleaning up the top side to prevent shorts, the bottom looks like it barely needs work!
richfiles:
And a detail shot underneath some wires, as well as the larger of the three modules. I got a kick out of the fact that they used that big 2 row header for only 2 conductors!
MrSlack:
That's actually considerably less terrible than I thought it was going to be. Thanks for posting the details.
Richard Head:
I had a look at the schematic. They use a full bridge topology on the primary side and a single ended (forward topology) on the output. Un-F#cking-believable. :palm:
grumpydoc:

--- Quote from: Richard Head on April 21, 2016, 06:35:41 am ---I had a look at the schematic. They use a full bridge topology on the primary side and a single ended (forward topology) on the output. Un-F#cking-believable. :palm:

--- End quote ---
Could I pick your brains a bit for an explanation of which bits go with your comment above (well, I can see where the H-Bridge is) and why what they did was less than optimal.

As above I've always been puzzled why Q401 just looked to be a linear reg with no pre-regulation. Voltage feedback looks to go to the TL494 via R302. THat doesn't feel right because if you try to get 5V @ 20A out of this PSU (which should be well within its capability) the FET is going to try to disspiate 900W which doesn't add up.

Anything to help increase my understanding of the design would be great!
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