I've been looking through the forums for a while lately and I like what I see. Anyway, I am a EE student at UT Arlington and I like to take stuff apart to figure out how it works or in this case, why it went down in flames!
There have been a LOT of PC switching PSUs that have been just failing to hold rated load, overheating or even shooting out little bits of flaming shrapnel (bits of rectifier) out the back.
Too bad I don't have pics of the unit but here's what I found in a customer PC:
The PSU was labeled as a 450W PSU but only weighed about 2.5 pounds, I've seen 200W units with more substantial construction. The 12V rail said 30A continuous on the label.... the 12V rectifier had an absolute max rating of 15A! Needless to say, it was toasty, well very toasty, it had a nice chunk missing!
The 3V and 3.3V rectifiers were also similarly undersized but not toasty. The installed rectifiers were in TO220 packages... the correct one would have been in a much larger TO247 package.
No EMI/RFI filter was present at all, not even a cap. This explains why my radio reception went out the window when I turned the ailing PC on.
To add insult to injury, the line fuse was missing!!! On the PCB was a notice: RISK OF FIRE: Replace with same type and rating of fuse. The fuse holder was not present, what was present was jumper wire. This was not a DIY thing, all the soldering was factory! Yikes....
Other sins: 20AWG wire where 18 or even 16 would be called for, counterfeit capacitors, and a sleeve bearing fan.
So how did I find out all of this? Well, this PC came into the shop for a spontaneous reboot complaint (this is 90% PSU or capacitor plague related). I opened the case and saw the Powmax PSU and knew what was wrong but just to make sure, I decided to do a test with a multimeter. Well, when I fired it up, it decided to die right there. The rectifier shorted, the PSU overload protection circuit (switching transistor drive kill) was out to lunch and the smoke poured out. A trace on the PCB burned and cut the power.
The customer is extremely lucky the entire PC was not fried, the thing had a crowbar circuit that worked! The computer itself was put together by a now defunct PC shop in town that was infamous for using shoddy goods. I have fixed many of their POS rigs, I had been stealing their customers for a few years and so did every other honest shop until they folded.
I'll see if I can find the pics I took of a similar, but not quite as bad unit that failed in a friends computer. Somewhere I have pics of a Raidmax "420W" in contrast to the 400W Fortron unit in my PC. The difference is astounding.
Here is a PARTIAL list of known trash PSU makers:
Powmax/Leadman
Deer Computer (A.K.A Allied, Austin, Premier, L&C, etc)
Raidmax
Codegen
Young Year (Aspire/Apevia, older Ultra units)
Logisys
Coolmax
Sunbeam
Most trashy PSUs have at least a fuse, but many leave off the EMI/RFI filter and all of the ones on the list are grossly over rated pieces of Chinese junk. They are the Zinsco of the computer world.
What is sad is I know some class mates that STILL buy them for their own PCs. Oh well, school can't teach you everything. An ounce of experience and common sense is worth quite a bit more than a pound of theory. The EE professor almost had a stroke when he saw a similar board, the Physics prof had no clue why it was all wrong except for the missing fuse! :P
The FTC and CPSC need to step in on this, the BS has gone on too long. These units could cause a fire, at the very least they could (and have!) destroy a computer and the data within.
