momaka wrote on 2025-07-18, 07:35:

But this has nothing to do with the industrial PSUs I'm talking about. Most of them come with 5 screw terminals: AC input (L & N), ground, and output (+) and (-). The ground terminal is highly RECOMMENDED, but OPTIONAL. It is isolated from the PSU output terminals, but you could reference one of these to it, if desired.

The B2B sector (industry) implies the presence of skilled employees, due to which it consciously goes for reducing electrical safety and cost.
And then once a year the housewife gets an electric death in the shower because she bought a charger without galvanic isolation on AliExpress.
It's better not to do that.

OK, I desoldered what I think is the 12V diodes (MUR1510CT, in TO-220 package), and both diodes in the package test fine on my Fluke multimeter -- OL one way, and 400-something mV of drop the other way. So no luck there.

Also, I did replace all the electrolytic caps -- the Jackcon, etc. were what was available through Jameco, and while they may not last as long moving forward, they all tested OK on my LCR meter before I installed them.

Any ideas what to try next?

Thanks!

Also, I did double-check the 115V/230V switch, and it is in the correct position (115V for United States) and shows proper continuity -- I worked it back and forth a few times just to make sure.

momaka wrote on 2025-07-18, 04:17:

I've something similar too, except instead of light bulb sockets, I have 2 wall outlets (and a switch) wired in series. One outlet is connecting my DUT (device under test), while the other is for connecting my "current limiting" device (e.g. desk lamp with incandescent bulb or floor lamp with a high-power halogen bulb... or when heavier currents are expected/allowed, I use a 2 kW space heater or 700W/1.4 kW mini oven.) Yes, such large "current limiting" appliances can indeed take too much space on the bench (and I don't keep them there for that reason)... but sometimes, there's just no other alternative to such high power "resistors" - namely when testing ATX PSUs with APFC circuits, as those APFC circuit absolutely do NOT like low-power current limiting devices (e.g. 100W or lower light bulbs.)

I also have such a "series plug" device - but almost never use it. The problem with big heaters etc.
is that they take longer to get hot - so higher that wanted current occurs longer, and more often than
not it's long enough to cause damage.

What I do use more often, is a setup with 1A, 2A, 3A and 5A circuit breakers.... (I only use one at a time, otherwise
trip characteristics aren't terrible predictable).

I've also got one with Bakelite screw terminals where I can fasten a piece of wire to be a "homemade fuse".. I spent
a few days testing(*) various "thin" wire types to be able to create some very specific current limiters. Also not one I
use a lot, but very handy when I need it.

(*) Fairly easy to test current trip with a 5A ammeter, some high power resistors and a variac.

biggieshellz wrote on 2025-07-18, 22:15:

Any ideas what to try next?

Thanks!

with minimal PSU load ( waste HDD, which has not yet been disassembled into magnets)
- c5/6 each must be charged to 110V AC (for US) *1.4 = 150Volt DC
- C9 - measure for capacity and resistance. If it is bad, then this capacitor will limit the transmitted power.
- R/C/D around power BJT - incorrect driving of BJT.
- Power BJT - Starting from the fact that one of them may be broken and ending with the loss of gain. It is better to check by replacing them with similar ones.
- driving circuit- may disrupt self-oscillations during startup.