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Old 03-01-2022, 10:25 PM   #3168
momaka
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Default Re: Power supply build quality pictorial. part 2

I concur with PeteS - this is a Newton Power PSU made by Delta. Probably late 90's or very early 2000's - think Pentium II and 3 era / 1st "gen" slot A or socket 462 AMD Athlon. So output-wise, it was probably rated for 200W or less, most of which was for the 3.3V and 5V rails... though not too much, because after all, the 20 Amp rectifiers on the 5V and 3.3V rails probably limit(ed) the output current to 15-16 Amps, since this is a forward-converter design. Thus, the combined 3.3V and 5V output was likely rated around 110-120 Watts. The 10 Amp rectifier on the 12V rail probably limited the output to 6-7 Amps... which comes out to another 70-ish Watts... and that's your 200W.

That said, I don't think that primary transformer is ERL38. Measure the top part in mm and see. It's probably 28 mm across (ERL28)... which for 200W is adequate. I've seen early Delta/Newton and Bestec use these smaller transformers back in the day, and it was never an issue.

Regarding the "1004BL" chip on the primary side - that's very likely an equivalent to a UC384x series (e.g. UC3842, 3843, and etc.) current-mode PWM controller and it's *not* for the 5VSB. It's for the main PS and drives the MOSFET closer to the main transformer. The other MOSFET is for the 5VSB circuit, which is a 2-transistor self-oscillating design with feedback. You can actually see some darkening of the PCB near the 5VSB circuit and its "startup" cap, suggesting this cap has started to go (or has gone) bad. However, the actual reason was probably diode D901 behind it. Not sure why, but Delta liked to use standard 1N4002 diodes for the primary-side auxiliary rail (which feeds the 5VSB's driver transistor and also the PWM controller for the main PS) instead of proper fast-recovery diodes. I made a detailed post about it here (a little further down in that post, after the recapping of the PSU):
https://www.badcaps.net/forum/showpo...postcount=3136

And very likely, the 5VSB circuit on your Newton PSU above probably looks very similar to this:
https://www.badcaps.net/forum/attach...4&d=1621301619
In the case of the above schematic, since it's from a newer Delta PSU (made around 2007 or so), the diode in question is D951.

Quote:
Originally Posted by RukyCon
And the -12v rail (which appears to be derived from the 3.3v rail if i'm not mistaken)...
I'm pretty sure that's not it. -12V rail should be generated from it's own tap on the main transformer... and from what I can see from the underside / PCB shot, it is. It appears to be that first pin on the bottom of the transformer, as seen in this picture:
https://www.badcaps.net/forum/attach...9&d=1646129626
Then it goes up and through a diode, and into the main output toroid.

I know probably none of this matters to you, since you said you're not going to fix this PSU... and I don't blame you! With a broken PCB like that and a "hottie" 5VSB circuit, it indeed isn't worth fixing, unless you really wanted an era-appropriate PSU for a Pentium II / 3 PC. In fact, I'm glad to hear you're going to salvage it for parts - there should be plenty of useful components from this PSU. If you're going to discard any parts from it, though, let me know - I'm mostly interested in the 5VSB transformer. I have a PSU that needs one. The 2-transistor circuit burned it up pretty good. I was actually going to rewind it (and probably still may do that)... but perhaps as a backup? ... well again, only if you're going to discard it. Otherwise, I probably can salvage one from the 10's of PSUs I already have. I tried one from a 5VSB circuit of a single-transistor PSU without feedback, but the pri. aux. winding voltage is lower. I made it work after some modifications, but the low pri. aux. voltage is inadequate for the PWM controller of the main PS.

Quote:
Originally Posted by RukyCon View Post
Correct me if i'm wrong, but did some PSU manufacturers use overrated diodes because they would dissipate less heat when used at a lower current? (compared to their lower rated counterparts) I feel like i remember hearing that here before.
Yes, this is exactly it.
The PSU was likely rated for either 1 or 1.5 Amps (or maybe 2 Amps if it was a really early 2000's model ). So by using a 5 Amp diode, that makes the diode run much cooler. SB560 is also Schottky type. If they used a regular fast-recovery rectifier, the dissipation would have been a lot worse. I kind of showed what happens when you do that with this PSU's fix here:
https://www.badcaps.net/forum/showpo...07&postcount=2

Quote:
Originally Posted by RukyCon View Post
Anyway, i have many more PSUs that i plan on posting here someday.
You and me both.

Last edited by momaka; 03-01-2022 at 10:39 PM..
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