PcBytes wrote on 2025-03-16, 12:50:
Of note - if possible, up the capacitance to 3300uF. Almost every 2700uF cap I've seen, regardless of manufacturer, has been unstable.
Yeah, it's like an "unloved middle child" size that usually comes in the same physical size as 2200 uF (at least, that seems to be the case with most manufacturers) and has similar specs too. Often when I've measured these, they were closer to 2200 uF than they were to their nominal 2700 uF rating.
So I agree - either up the capacitance to 3300 uF or go lower to 2200 uF. Neither would be detrimental to the circuit. My experience with buck-type VRM circuits is that you can often do 2-3x the stock capacitance, and still all would be fine. Actually, if anything, you'd get improved (lower) ripple & noise. The only reason the manufacturer didn't do is because it wasn't totally necessary for the function for the circuit. With that said, you can go even with 3900 or 4700 uF caps if you like.
gdjacobs wrote on 2025-03-17, 02:00:
What is the series identifier? MFZ? It's advisable to match ESR rating on the replacement caps, and some of the more notorious Rubycon caps can best be matched with polymers these days. Same thing as ultra low series from Nichicon and Nippon Chemi. Using voltage, capacitance, case size, and series you can find stats from the data sheet. From the ESR and ripple listed you can find a match from your supplier of choice.
+1
My guess would be the caps shown in the picture above are probably MCZ series. From what I know and have seen, MFZ was typically a custom series for the Xbox 360, and I've only seen them in black with dark gold writing / stripe for the negative... at least in the 6.3V 2700 uF "flavor" (later on, when Xbox 360's switched to 6.3V 820 uF MFZ, these often came as black with white text writing / stripe for the negative.)
Anyways... I completely agree and would also strongly suggest to use polymer capacitors here instead of regular electrolytics, seeing how the two MOSFETs below seem to run quite hot, based on what I'm reading elsewhere.
-OR-
You could do a combo of ONE electrolytic cap (to get the advantage of higher capacitance) and ONE polymer (to get the advantage of better heat durability, ultra-low ESR, and very high ripple current capability.)
I'd probably tackle this with 1x 1200-2200 uF polymer and 1x 3300-4700 uF low-ESR electrolytic (something along the lines of Panasonic FR, FM, FS or Rubycon ZLH, ZLK, ZLQ, ZL, or Nichicon HW or HV, or United Chemicon KZH or KZM.)
-OR-
You could just use two polymers with capacitance somewhere in the range of 1200-2200 uF.
These two capacitors appear to be the pre/ input filters to the buck-type VRM circuit with the two MOSFETs below it. So the capacitance here isn't that critical. With good low-ESR caps, even 1/2 to 1/3 the capacitance would be fine.
Soap wrote on 2025-03-16, 11:41:
Thanks so much for advice, just finished desoldering and started cleaning motherboard.
The capacitors i removed are 6.3v 2700uF, what would be a low ESR rating?
For Rubycon MCZ series... this particular size doesn't exist in the datasheet. So I guess these are either custom-size MCZ series or the same custom-made MFZ series the Xbox 360 used. Either way, these two series are pretty close to identical in specs... so it's really a matter of their case size.
If these caps are 10 mm dia. x 20 mm height, then they probably have the following specs: 0.011 Ohms ESR (11 mOhms) and 2770 mA ripple current
And if these caps are 10 mm dia. x 25 mm height, then they probably have: 0.009 Ohms ESR (9 mOhms) and 3230 mA ripple current
Looking at my cap datasheets, you can probably use either:
1) United Chemicon PCS series polymers... the 6.3V 1500 uF cap size is rated for 10 mOhms ESR and 5560 mA ripple current.
2) Panasonic OS-CON SEPC series polymers... the 6.3V 1500 uF cap size is rated also for 10 mOhms ESR and 5560 mA ripple current
3) Nichicon...
---a) FPCAP R7 series... 6.3V 1000 uF cap is rated 7 mOhms ESR and 6100 mA of ripple current
---b) PLG polymer series... for 6.3V, you have either the option of 1500 uF or 1800 uF, both of which satisfy the ESR and ripple current requirements.
majestyk wrote on 2025-03-15, 12:52:
The inductor just overheated, chances are it´s still working.
Unfortunately, no, it won't be working as intended anymore. Most ferrite cores loose their magnetic properties above 100-120C, with some (like the common -26 and -52 Micrometals materials) quickly degrading past 80C.
For the wire on that toroid to melt like this, it means the temperatures of the core were in excess of 350C!!!
FWIW, I've repaired PSUs with burned output inductors like this. You cannot simply just rewind it - the new windings will burn out again, due to the core not having the same magnetic properties. So for these, a replacement was absolutely necessary.
-FORTUNATELY- for the O/P, this inductor appears to be just a simple noise/EMI/RF filter leading to the two bulged/leaking electrolytic caps, so it's not a deal-breaker if this toroid (and its burned wire) are acting like a shorted wire now. Well, in some scenarios where the board is under high stress, it might, as the now-not-doing-anything toroid inductor would be letting excess noise/EMI/RFI back upstream, possibly causing another circuit to pick it up and get signal interference.
SO... it's a good idea to replace that inductor, IF possible with same or similar one (I can elaborate on this if needed in another post.) But chances are, you can probably indeed just rewind it with new wire... or even leave it AS-IS (so long as the wire has not opened / cut anywhere), and the board will still work.
Really only the caps need to be replaced, and the two MOSFETs directly below them checked for short-ciruit via resistance tests (DON'T use continuity on your DMM, or you might think the "lower" MOSFET in the circuit is shorted, simply due to the fact that this one will usually be in parallel with the core of a chipset/CPU/GPU... causing a low resistance to appear between its Source and Drain.) If the MOSFETs pass, just replace the caps and that should be all, really.
For the burned inductor, if really wanting to replace it, I imagine even a simple rod core "PI coil" inductor would be sufficient to eliminate VRM noise back upstream... but if not, then a Micrometals -2 or -14 or even -8 material core with a few windings might do the trick too. All of these were low-permeability high-frequency -rated type cores, IIRC.
