HQ POWER PS613 unleashes its power!

Ludo | 21 mai 2017
This lab PSU is also sold by Velleman, under the same product name.
I own it since almost 8 years and I never had to complain about it, aside from its voltage drift that forces to regularly adjust the voltage output.
Therefore I had no reason to doubt about it when I needed a 12V power supply for powering the IP cameras I quickly installed, before going to a 2 weeks holidays off the house.
Well… what happened next proved me wrong!

I could access to all my IP cameras during the first week, with most of them powered by fixed DIN rail PSUs, but then the freshly set up cameras suddenly went off the radar. I should have panicked, but I just thought something minor happened, like a blown fuse. What happened actually was a little bit more troublesome.

Back home, I found the PS613 displaying an incoherent voltage, 48V, which is quite worrying for a PSU that can’t go higher than 30V! The current limit was obviously active, which was a little bit more serious situation than what I thought at first.
I’ll come back later, in another post, about what happened to the IP cameras.
A quick search on the internet could not point me to any lead or schematic, so I just hoped to be lucky enough and tried to blindly repair it.
First of all, I found a brownish mark on the board that’s attached to the black heatsink, right under the through-hole diode bridge (KBU606). I replaced the diode bridge with an equivalent part but the PSU was still faulty. Then I checked all transistors with a multimeter, testing both junctions in the diode test mode, and couldn’t find any defective part. I Finally took a look at the ICs and started to replace them one by one, starting with the parts names I had on my lab. The PSU went back to normal right after I replaced the IC labeled « N3 », located on the front board (see picture below).

Everything looks fine now:

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