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Old 02-28-2022, 10:03 PM   #3162
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Thumbs up FSP Group Inc. AX400-PN

Got this one a while back on eBay with a bunch of other old PC parts. Namely, it was with the ASUS K8V-SE Delux motherboard shown in this build, along with the accompanying HDD and RAM. Everything worked from that parts lot. The PSU was just unstable, because it had bad caps, as you will see a little further below.

Anyways, let’s show it… as usual, starting with case shots:
FPS Group Inc. AX400-PN (1).jpg

FPS Group Inc. AX400-PN (2).jpg

As can seen, pretty standard gray-box PSU with 120 mm overhead fan and non-sleeved wires – simple! (Just the way I like them.)

Label shot next:
FPS Group Inc. AX400-PN - label.jpg

The label shows a pretty honestly-rated PSU – 350 Watts continuous and 400W peak, with 300W for the “dual” 12V rails combined (i.e. 25 Amps.)

So let’s see what the internals hold and if they can support the label’s claims.
FPS Group Inc. AX400-PN (3).jpg

FPS Group Inc. AX400-PN (4).jpg

Well, for a 350W continuous PSU, this looks really good – in fact better than what the pictures show here. In particular, the main transformer is ERL39 size (39 mm wide), which should definitely be enough. Also, the main output toroid is a T130-26 part with plenty of copper on it, so it too should be more than adequate. The design is a half-bridge with BJTs, so the Micrometals -26 core of the main output toroid should be fine here. Both heathsinks are quite hefty too. All in all, I can’t think of anything to complain about. Perhaps I can try to pick on the lack of a NTC thermistor on the input? Seems like that might actually be a valid concern… but it may not be, as there is also a large multi-turn single-mode choke on the input. So I imagine that could attenuate inrush currents perhaps. OK, I know what I can complain about – the tan/brown conductive glue. But it hasn’t turned brown yet, suggesting the PSU has been running pretty cool.

Anyways, here is a shot of the primary side in more detail:
FPS Group Inc. AX400-PN (5).jpg

No complaints here either. Primary caps are Teapo LXK @ 200V and 680 uF – good enough for the 350W continuous rating. Main BJTs are a pair of D209L in TO-3P case. Bridge rectifier is an 8-Amp part (GBU8J.) There’s even space behind the primary heatsink for a PPFC coil, which wasn’t installed on this unit. On the plus side, this should allow the overhead 120 mm fan to push air easier through the PSU – especially on the primary side.

Moving onto the secondary side…
FPS Group Inc. AX400-PN (6).jpg

FPS Group Inc. AX400-PN (7).jpg

Ah, now we see what the problem is: bulged caps. In particular, these two are the output caps on the 12V rail – 2x Teapo SC, 16V, 2200 uF. I think that’s probably the reason why the seller on eBat decided to “scrap” the system and sell it for parts. Shame, because this is a good PSU and was an easy fix overall. The motherboard is quite nice too and probably getting harder to find now.

Next, here is our “noise killer”:
FPS Group Inc. AX400-PN (8).jpg

There is an LM358 dual op-amp IC on the other side of that board, along with the power transistor. The NTC for the fan controller is located next to the secondary heatsink on the main PCB, right below the 3.3V rail’s output toroid.

Speaking of the fan, this is it: a Yate Loon D12SH-12, rated for 0.3 Amps @ 12V.
FPS Group Inc. AX400-PN - fan.jpg

I just opened the PSU for cleaning this week after using it for close to 3-4 years now (mostly in my gaming PC - the Optiplex 790 from the Post Your System thread.) Although I didn’t put it through any 24/7 use, I did use it for about 1-2 hours a day on average… and that’s doing mostly gaming or CPU-intensive tasks. So after a few years of this, the fan was starting to sound a little dry. For whatever reason, I didn’t lube it when I recapped the PSU back then. The factory grease was pretty much completely dry now. After a good cleaning with IPA and a quick resurface of the sleeve bearing, followed by more cleaning and addition of fresh oil, the fan runs like new again.

Lastly, here is a shot of the underside (the solder side):
FPS Group Inc. AX400-PN - solder side.jpg

Overall… pretty good!

That completes the image gallery for this PSU. A more detailed component breakdown can be found below.

Primary Side:
* EMI/RFI filtering: three 472M Y2-class caps; two X2-class caps (1x 0.47 uF? and 1x 0.1-0.22 uF?); two CM chokes and one SM choke
* Protection: F8AL or F10AL fuse; 2x MOVs across each primary cap; NO NTC thermistor
* Other: GBU8J bridge rectifier (not heatsinked)
* Caps:
*** 2x Teapo LXK, 200V, 680 uF, 22x45 mm
*** 1x Teapo SEK, 50V, 22 uF, 5x11 mm (5VSB startup / run cap)
*** 2x Teapo SC 50V, 2.2 uF, 5x11 mm (part of BJT driver circuit)
*** 1x 2.0 uF 250V P.P. for main PS transformer coupling
* Main PS (H-bridge topology): 2x D209L NPN BJTs (TO-3P); 51-Ohm 2-Watt resistor + 102K 1KV ceramic cap for snubber ciruit
* Transformers: ERL39 (39 mm) for main PS; ERL/EE16 (16 mm) for BJT drive; ERL/EE16 (16 mm) for 5VSB

* DM311 (P-DIP8) for 5VSB
* FSP3528 (P-DIP20) custom PWM chip with protections from FSP
* LM358 (P-DIP8) for fan controller

Secondary Side:
*Output Inductors: T130-26 common-mode toroid for 5V/12/-12V; T106-26 (25 mm dia.) for 3.3V rail mag-amp filter

* 5VSB
*** 2x Teapo SC, 10V, 1000 uF, 8x20 mm caps with PI coil between
*** 3Amp or 5Amp diode rectifier
*** PI coil: 32-turn, 22 AWG, 3.5x25 mm rod core

* 3.3V Rail
*** 1x Teapo SEK, 10V, 3300 uF(?), 10x30 mm cap before PI coil
*** 1x OST RLP, 10V, 4700 uF, 10x30 mm cap after PI coil
*** 1x 30 Amp or 40 Amp (TO-247) Schottky rectifier
*** PI coil: 5.5-turn(?), 14-16 AWG, 5x15 mm rod core
*** Load Resistor: 10-Ohm, 2 Watt

* 5V Rail
*** 2x Teapo SC, 10V, 3300 uF, 10x30 mm caps with PI coil between
*** 1x 30 Amp or 40 Amp (TO-247) Schottky rectifier
*** PI coil: 5.5-turn(?), 14-16 AWG, 5x15 mm rod core
*** Load Resistor: 15-Ohm, 3 Watt

* 12V Rail
*** 2x Teapo SC, 16V, 2200 uF, 10x30 mm caps with PI coil between
*** 2x SF1603g (16 Amp, 150V, TO-220) ultra-fast rectifiers in parallel
*** PI coil: 10-12-turn(?), 14-16 AWG, 5x30 mm rod core
*** Load Resistor: 1-KOhm, 0.5 Watt

* -12V Rail
*** 1x OST RLP, 16V, 220 uF, 6.3x11 mm cap after PI coil
*** 2x 2-3 Amp (?) diodes
*** Load Resistor: 1-KOhm, 0.5 Watt

* Auxiliary Sec. Side
*** 1x Teapo SEK, 50V, 47 uF, 6.3x11 mm cap

*Other caps:
*** 1x Teapo SEK, 50V, 4.7 uF, 5x11 mm
*** 5-6 mm height: 1x 16V 16 uF; 1x 35V 10 uF; 1x 16V 47 uF; 1x 50V 1 uF

* output wires: 20+4 pin ATX, 1x 4-pin 12V CPU, 1x 6-pin PCI-E, 6x Molex, 1x floppy, 2x SATA… all rated for 300V and 18 AWG, except floppy wires.

And that’s pretty much it. Up next follows a cap diagram and my partial recap. Stay tuned!
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