Logisys 575W

[etnietering]

Re: Logisys 575W

OK here are the pictures -

The naked bridge rectifier - with a little of the artic silver i couldn't get off


And here's an overhead shot of the whole thing, you can see the whole input filter now, including the extra X cap I added to the power cord socket


So now this one is pretty much done....but I bet I'll have it open again in less than a week....

[Newbie2]

Re: Logisys 575W

Looks professionally done there etnietering, awesome work!

Looks very dependable for I guess 250W-300W operation, I'd say perfect for computers using Northwood Celeron/Pentium 4 or even lower-end Prescott Pentium 4 processors. Very nice primary input section, and the illusion of a big secondary side due to the large Panasonic caps. A++++++++++++ work

If Logisys power supplies came directly from the factory looking like that then they would be an excellent value for the price.

[Gianni]

Re: Logisys 575W

You have done a nice job but I'm sure something is not done in the right way:
the input coils are usually coupled (common mode or differential mode) for EMI compatibility so I don't think that 2 separated inductors works correctly.
Moreover the X caps are dimensioned together the input coil and only testing tha PSU with EMC analyzer you can see if the filter works correctly.
Adding coils and caps without doing the test doesn't mean you have a good PSU respect to the noise/interference it can produce on the power line.

I think that replacing bad caps or undersized diode can improve a PSU but adding input filter can be useless because only the designer with the right equipment can test PSU for EMI compatibility.
So I will never try to make a better PSU starting from a "bad PSU" (w/o EMI filter).

Ciao
Gianni

[Newbie2]

Re: Logisys 575W

Well even if his filter doesn't actually work it will still be nice to make the PSU not look like a "gutless wonder".

[momaka]

Re: Logisys 575W

the input coils are usually coupled (common mode or differential mode) for EMI compatibility so I don't think that 2 separated inductors works correctly.

You're probably right. I've seen separate toroidal coils one next to another for input filtering, but not separate PI coils.
Okay, the PI coils might not be efficient, but at least it's not jumper wire .
Like you said, it would be interesting to test this unit and see if and how much the input PI coils improved EMI.

[everell]

Re: Logisys 575W

Newbie2, perhaps you could persuade you dad to give us some pointers - then we would know for sure if we are heading in the right direction.

[etnietering]

Re: Logisys 575W

I wish I had a way to measure the input to see if the EMI filter actually helped. In everything I've seen, it has one of the two line coupled coils, but I measured the holes in the pcb and searched and searched and couldn't find one that fit. So I did the best I could, and I'm sure it's better than just the lame jumper wire. Same goes for the input caps - I'm sure they're not optimal, but they beat having nothing at all, which is what it had before.

And yeah, I've put about 15 dollars up upgrades/repairs into this 15 dollar power supply...but now I trust it to be a backup, and I have more confidence in myself to work on other power supplies/other stuff. It's been running for over 24 hours now powering a couple fans with no problems

[ratdude747]

Re: Logisys 575W

conclusion: Logisys SUCKS!

[370forlife]

Re: Logisys 575W

yes, they do.

[ratdude747]

Re: Logisys 575W

thats the problem with crap supplies- they are too light to be a paperweight

[370forlife]

Re: Logisys 575W

I actually have a old powmax I use as a doorstop in my room.

Whenever I have all my windows open and theres a big gust it will slam my door shut, so I used a powmax for that.

The wind had no problem swinging the door with the powmax between it and the door frame, crinkled the powmax a little. Sad because it did nothing to the wood door or frame.

[etnietering]

Re: Logisys 575W

OK well I've done a few more upgrades to my logisys, and now I've run into a problem....

First, I added two scavenged Y caps to the power recepticle - that went fine.
Second, and what is causing problems, is I upgraded the secondary side silicon. Here are the changes:
3.3v: 60v/20A -> 45v/60A
5v: 60v/30A -> 45v/60A
12v: 200v/16A -> 250V/40A

I did this to make sure the secondary side could handle the rated output (even though the transformers/primary side can't).
So the problem is, when it tries to turn on, I get a short whine (less than a second) and then nothing...no voltage anywhere, no fans, lights, nothing. From what I've read, that indicates a short or something, because the oscillator driving the primary switchers can't keep up...or something. I've examined the parts I've soldered at least 5 times, and can't see any problems. I checked them with a voltmeter, and there are no shorts. I also was sure the isolate each component from the heatsink, so there are no problems there.
I see two possibilities for the problem:
1) The parts I used are of lower voltage than the originals (for 3.3 and 5v), and this is causing reverse breakdown.
2) For some reason this has changed the output side enough so that the primaries don't work right.

Now I don't think it's the first one, because I've seen units with 30v parts here...but I suppose it could be. Any thoughts anybody? Thanks!

[linuxguru]

Re: Logisys 575W

You have good +5Vsb, right? 45V reverse breakdown should be sufficient for the +3.3v and +5v rails - I've seen xx1545 rectifiers there, i.e. 15A, 45V. Is the polarity of the replacement rectifers the same as the original, typically common cathode, i.e o-->|--o--|<--o ?

[etnietering]

Re: Logisys 575W

The standby voltage registers at 5.14v, which is fine, and I made sure that the diodes are all of the common cathode type.

[370forlife]

Re: Logisys 575W

Did you check all of them out of circuit?

[etnietering]

Re: Logisys 575W

Well I replaced all of the tiny electrolytics (2.2uF - 10uF) with UCC KME series ones from an old AT power supply, because I've read here they can cause problems. Still doesn't work though...still get the little almost chirp for a fraction of a second when I try to turn it on. +5vsb still reads 5.14v....
Any thoughts?

[momaka]

Re: Logisys 575W

KME are general purpose caps, but rated for 105C. I doubt that will be a problem, but thought I should just let you know.

[etnietering]

Re: Logisys 575W

Yeah, it took some digging on the UCC site, apparently they were discontinued a few years back. They were replacing some blue and purple BH brand general purpose ones though, so I also think it's not a problem.

sorry I didn't see your post 370, it was one minute before mine. I didn't test the parts out of circuit, but they were brand new from ON and so I just assumed that they'd work...I don't think I'll be able to take them out again though, I did enough damage to the pads the first time....

Thanks for the input guys

[etnietering]

Re: Logisys 575W

Well I took the secondary heatsink and all attached silicon out (it's amazing what a more powerful soldering iron can do you for you ) and they all test good. They all conduct from the outside in, but not the inside out. What's the next step? 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? Or would that totally wreck it? Thanks!

[370forlife]

Re: Logisys 575W

I'm concerned about the new 12v diode. 250V is something I have never seen before. Try the original or maybe just a simple 30A, 45v.