Logisys 575W

[etnietering]

Re: Logisys 575W

There is noticeable heat stress discoloration around where the +12v rectifier goes, indicating to me that the original one was under a lot of stress, so I'd rather not use it again unless I have to. Unfortunately, the spot on the PCB for the +12v rectifier will only accommodate a TO-220 package. In that package I have the following options:
40A/250V (what I put in)
30A/150V
60A/45V

I could look through my stash of used parts for something else though...

[370forlife]

Re: Logisys 575W

Try the 60/45 if you don't mind...wasting it...I guess you will just have really stable 12v voltages now.

[etnietering]

Re: Logisys 575W

I have a 30A/60V one that I salvaged out of an old AT unit. But I'll use the 60A/45V new one, I got 10 of them from ON for a $0.11 each...so I don't mind using it

[370forlife]

Re: Logisys 575W

I have a 30A/60V one that I salvaged out of an old AT unit. But I'll use the 60A/45V new one, I got 10 of them from ON for a $0.11 each...so I don't mind using it

Want to borrow one of my 30v/70A parts I got from them?

[etnietering]

Re: Logisys 575W

hahaha well I got it in, and there's a change when I try to fire it up: before it would just chirp and that was it. Now, it chirps and the LEDs I put in light up for a second and the Fan twitches. So this leads me to believe that the problem was before with the 12v (both the fan and LEDs are on the 12v), and now there's a different (or unfixed) problem.

[etnietering]

Re: Logisys 575W

success! I took it apart again and noticed a solder bridge on the 3.3v rectifier. So I removed that, and now it works! Yay! So the problem was either my soldering on the +12v part, that I didn't know about, or that part itself. Hmm I didn't think having too high a blocking voltage could be a problem, but I guess I was wrong. Thanks for the help! The next upgrade will be getting a board made for my run-the-fan-off-the-standby-power circuit, and install that

[370forlife]

Re: Logisys 575W

Sounds like it has some sort of short protection if it was shutting itself off with that solder bridge. Interesting. Did you replace the primary switchers too? If so, then you just have to do the transformer...he he he. Thats fun.

[etnietering]

Re: Logisys 575W

Nah I didn't bother replacing the primaries, they're rated for like 8 or 9A, which is far more than this piece of junk is ever going to need. And I'd be replacing them either with something that's 15 years old, or with my crazy ones from ON, and I don't want to waste them on this piece of junk....and I don't think I have a transformer that would be worth using - I think all the other ones I have are either the same size or even smaller!

[momaka]

Re: Logisys 575W

Good to hear you got it working .

I agree with 370forlife, though, it was probably the bad soldering on the 3.3v that was shutting down the PSU. I don't see why the high blocking voltage on that 12v rectifier would be a problem. Higher DC blocking voltage just means better protection in case something goes bad on primary.

Well either way, the original 12v rectifier was likely adequate as well. As for the PCB discoloration/burnt spots, I think that is due to the heatsink being too thin.

Should I try to turn it on without any of these diodes and see what kinds of voltages appear across where the diodes would be?

Probably not a good idea. Not sure what will happen, but there's always the possibility of the primary transistors blowing (if PWM IC doesn't see any voltage on output, it could turn pulses up on the primary transistors until it shorts them).

[Krankshaft]

Re: Logisys 575W

Unless you know where the feedback is coming from it's not a good idea.

The PWM only needs to sample one output and compensate for it if one secondary output is in voltage tolerance all of the others will be too (due to the transformer turns ratio).

As for measuring where the diodes would be unless you have a true RMS meter to measure the high frequency AC output from the switching secondaries you won't get the proper voltage anyways.

Meters that are not true RMS can only measure AC properly if it's a pure sine wave. A switcher outputs pulses.

[etnietering]

Re: Logisys 575W

Yeah I thought something like that might happen if I were to try it...that's why I asked And I checked the soldering at least a dozen times with the original set of replacements, and they were all fine - it was only after I took them back out, switched the 12v one, and put them back in, that there was a short on the 3.3v line...which is why I'm at such a loss as to what the problem was. There are also some heat marks around the transformer - probably because it was powering a computer with two 85W xeons - that's > 14A on the 12v from the CPUs alone, assuming 100% VRM efficiency, which is not the case. I'm quite surprised it didn't just explode as soon as I powered up the computer. It actually held up pretty well (the only thing I had to do while still using it was replace the current inrush limiter), although I melted the 4->8 pin 12v connector

[etnietering]

Re: Logisys 575W

Well I found some pictures I took of it after the first diode replacement - it looks the same now, except the middle rectifier is a B60L45G instead of a B40250TG.

But first, here's the new Y caps on the power socket:


And here's the secondary heatsink, with the new rectifiers attached, and the old rectifiers above. They are in this order: 3.3v, 12v, 5v


And here they are, almost visible reinstalled back into the PSU, along with all my Panasonic caps

[etnietering]

Re: Logisys 575W

Well I took the transformer out of my 500W aspire and put it into my logisys, and my first transformer surgery was a success Here's some pictures:

Here's the old transformer (yellow) next to the new one (blue):


Here's the logisys without it's main transformer - more heat marks on the 12v line:


And here it is with the new transformer. There's about 1mm of clearance between it and the fan case...


I think now it might be able to actually put out the 330W it's rated for, and maybe more beyond that.

[Newbie2]

Re: Logisys 575W

Beautiful work!

Now that power supply looks like a decent backup power supply that should last for a while.

[larrymoencurly]

Re: Logisys 575W

I don't think the bridge rectifier even needs a heatsink, all power supplies I've seen don't have one. His Dr. Pepper can heatsink is a little extra.

My 300W Delta has a small heatsink attached to its rectifier, but how does it help when it's barely larger than one side of the rectifier package?

[Wizard]

Re: Logisys 575W

This plate if it is copper or aluminum does help to spread heat to larger area instead of
relying on the plastic/glass particle matrix to dissipate heat to air is smaller due to poor
thermal conductivity.

Cheers, Wizard

[370forlife]

Re: Logisys 575W

I think now it might be able to actually put out the 330W it's rated for, and maybe more beyond that.

I know, I would love to hook up my yuelin to a load tester and see how far it goes.

[kc8adu]

Re: Logisys 575W

My 300W Delta has a small heatsink attached to its rectifier, but how does it help when it's barely larger than one side of the rectifier package?

good enough if the fan is running.useless if not.adds just enough surface area to do the job with the airflow from the fan.