Succesful repair: Maston SPS-9250 SMPS

Hey guys, figured i'd share about my todays repair accomplishment. I saved this 15v/25A PSU from going to dumpster, thinking if it could be repaired, or at least take a look inside. First i tried to look schematics and manuals for future use, if it would work like a charm after all. Those were found luckily easily enought.

Then, it was testing time. it's easy to say what happened when i powered it on, via variac, just for safety. NOTHING. Not even smoke came out, luckily thought. At first, i checked fuse, which was okay, even measured it with DMM. So, now i knew at least nothing dramatic ain't happened, as it is school equipment, SC/s are not that rare stuff. Next was more detailed measurements time. I noticed when studying schematics, that first IC was pretty close to main rectrifier bridge. So i measured did i got any voltage, it should get according to schematics. Nope, it didn't. This narrowed search a lot. Of course, i checked 'lytics and schottky diodes just to make sure about them.

Now then, next i measured bridge. Not even that got AC required....oh man, its transformer fault then, i bet. But, i noticed writing on schematics, that LC filter was left out. In my aknowledge, that fails rarely, so i checked that too, which was mainly big choke along with two caps, dont' know their official name. That filter turned out be fine. Now i measured just to make sure, that does ac voltage even come to primary side of transformer. Nope? Only thing i haven't checked so far, was switch. Turns out, THIS, very switch was faulty, or to be more specific, there was bad connection. Switch was 2p2t type, which i didn't have in stock currently, so i bybassed bad connection.

Well, this was nice refreshment, little bit balancing to normal stuff which i try to repair, which stays attempts!

Thanks for reading! :)