Electronics > Repair
Mastech HY5020E 50v 20a Bench Supply: Economical to repair?
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bitseeker:
When you've got the supply torn apart and clean, it'd be great to snap some high-res photos of the PCB for reference and fixing the schematics.
richfiles:
I can do that. You should see the photos I've taken of my PC case build and my custom mechanical keyboard!  ;D
When I start, I'll keep this thread updated.
grumpydoc:

--- Quote from: albert22 on April 20, 2016, 09:19:02 pm ---Also I may be wrong but it seems that the switching supply is not working as a tracking pre-regulator so Q401 can get very hot and even fall outside its SOA. It is rated at 200W at 25degrees. And probably is not a MOSFET suited for linear operation.

--- End quote ---
I have wondered about that in this design of PSU as well - but surely the thing would just blow up at high current/low voltage output settings?
Shock:

--- Quote from: CJay on April 20, 2016, 12:48:16 pm ---With the dire warning that if it's got auto input voltage sensing then using it on 220V with a series light bulb could just trigger the rapid, violent release of more smoke.

--- End quote ---

I've not read much about this occurring, have you got any instances or references where this has happened and how a good SMPS failed from it? I can only seem to find it mentioned on the repairfaq.org site. Would the same occur using a variac?
richfiles:
I'm 120v AC here (US), and that's what my input setting is set to. I do keep seeing a few references to 220v/240v here, so I thought I'd just mention that.
Man... I've never built a switching supply. Only ever worked with Linear ones. This will be my first switching supply repair, so be gentle!  ;)

The only thing I know for certain about switching power supplies, is how not to build one and throw a fake CE logo on them! :-DD Lookin' at you China...  ::)
 I know the basics of operation, the basics of how they work, etc. I just have not ever actually serviced one yet. I don't know what's typical of the controllers, and tend to follow schematics, instructions or guides to get through unknowns. I know well enough about upgrading to good high temp caps like Nichicons or Panasonics, and I can match a transistor or diode just fine. I used to do a lot of repairs as a profession, and got really good at tracking down parts lists and generating BoMs for them. These days, fewer professional repairs, but I still do this on occasion. More importantly, I will CERTAINLY take the best advice offered on more detail oriented suggestions, etc. I'll take into consideration the mention of C003 needing to be an X class cap, and I'll gladly take suggestions on Q401 This is the kind of gold I know I can find here, from people far more experienced than I am at this stuff. The whys behind everything... That's awesome too! Share why something should be different, why a specific change would be an upgrade, etc. I'll be listening. I wanna get this right. :-/O just know, it's all appreciated!  :-+
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