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  #31  
Old 05-08-2011
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I'm just restating. The article was a good thought, just maybe a bit misleading.
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  #32  
Old 09-20-2012
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Default A small correction

None of this text affects recapping or results in any way, but it might be still nice to correct some small mistakes in the article, so as to prevent incorrect information spreading, just in case someone actually reads the details and perhaps plans doing more than recapping (like I'm planning to do). I'm also aware of the age of the article, but since the article still exists and points to here for feedback...

I noticed that the second PSU of the article, FSP600-80GLC, has the same base design as a Zalman I'm working on (which is no wonder, as the zalman is actually designed/built by FSP, evidenced among other things by one of the sub-boards even containing a revealing "FSPxxx-60GLY" snippet). Most parts are in completely equal places.

And the small mistake in the article is under the 7th picture on page 3, with the text "That black thing between the big mag-amp coils". Neither of the coils is "magamp coil".

The left coil in the picture is actually a "coupled inductor" and the right side coil is just normal inductor. The coupled inductor is somewhat easily recognized as it has multiple different windings (although the same applies to "transformers" and couple other components of the same family). However, a magamp coil is pretty much impossible to tell apart from normal inductor visually; one needs to look for the magamp control circuitry to see which inductor it is working on, though it seems to be, at least for PC PSU, always the first inductor "after" (or next to) transformer (in the eletric path, not necessarily in the layout).

The coupled inductor indeed handles multiple voltages. In the zalman it handles +5V, +12V and even -12V. Though that -12V is peculiar one, as it doesn't filter that voltage, but generates it! (That was one of the wtf-cases for me, when I noticed that the other end of the -12V wire was connected to ground.) It doesn't even have a filtering coil at all, which explains some of its large ripple.

The normal toroid inductor on the right side is the first filter coil for 3.3V. It has the same purpose for filtering as the coupled inductor has for the other voltages, but naturally isn't coupled with any other voltage. (3.3V also has own independent regulation, so it wouldn't get all the benefits of coupling, and it would even be bad for some parameters). The second/last filter coil for 3.3V is seen in the next picture, just next to the toroid, towards the 5V red wires. (The another small coil peeking from under and just right of that second 3.3V coil is for 5V standby).

So where is the (only) magamp coil then? Looking at the second picture on the page, a corner of a smaller toroid coil can be seen behind and on the right side of the main transformer. That's the magamp coil.

--
A bit of background, not really interesting except maybe for a few electronics engineering geeks...

I've been digging into a Zalman ZM460-APS (and a bunch of older PSUs), not just to replace caps - well, that was the original idea, but after opening the zalman up bigger problems revealed themselves and changed the plans - but to also modify the secondary side for much improved operation with just one output voltage, sort of fixed voltage "lab supply". Read, it will get a totally new PCB, revamped voltage regulation/feedback, and hopefully some "ripple steering" magic if I can just remove the black goo from the coupled inductor to rewire it.

One thing lead to another and I stumbled on this quite nice "in practice" article. I was actually positively surprised by the "worse" result noise levels considering how simply the choice of new capacitors was approached. The result noises aren't significantly higher, even when the new caps could easily be of 10%-20% lower capacitance and worse ESR, especially if the manufacturer e.g. originally used caps with best binned values.

Having spent couple last weeks reverse engineering big parts of the schematic of each PSU, I have now quite a good idea on what part does what. Had quite a few WTF-this-can-not-possibly-work -moments which soon turned into learning and wow-it-indeed-works -enlightenments. And even more of holy-chinese-crap revelations with the older units.
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  #33  
Old 10-19-2017
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The original caps may have (or developed) a higher ESR; this could help damp out oscillations, and might explain why the ripple got a little worse.
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