Dead mini-ITX PSU

[D.M. Procida]

The PSU in my mini-ITX box seems to have died.

It's this PSU, as far as I can tell: (it certainly looks like that).

There's no internal fuse that I can identify, and though there's a generic-looking warning inside about only replacing the fuse with one of the same rating, there's no mention of a fuse on the label.

I can't see any blown capacitors in there either, but there's nothing coming out of it at all.

I think the PSU is discontinued, which means that the whole box is pretty much useless.

Annoying - I was going to give it away, but I'd hate to throw it away. It was happily runnng an ancient iMac motherboard inside there.

I don't know much about computer PSUs, but I take it that the chances of getting hold of a compatible replacement is slim?

Daniele

[The Natural Philosopher]

no, id say its quite high.

Got a vast rackmount case and PSU somewhere as well..

A mini ITX case complete with PSU is not that much more expensive either.

[Theo Markettos]

Electrically, there's plenty or similar or higher wattage that would do the job. So it's just a case of finding something of the right physical size with sufficient connectors for what you need. The web page doesn't give dimensions, but you can fit something of the same power but smaller (which do exist) if you can find a way to mount it in the case.

Theo

[Dave Liquorice]

That one has a 110/240v switch rather than auto switching. Maybe if yours has a similar switch it has got knocked or full of dust, checkit give it a waggle?

Unless it's *very* ancient and I wouldn't call mini-ITX very ancient or the case very strange you probably can get a replacement. PC parts are pretty much standardised in location of mounting holes fans etc.

[Graham.]

There will be a fuse on the PCB, It is often wire ended and soldered in.

Unscrew the PCB from the chassis so you can get to the underside. Using a meter on low ohms or continuity beeper range, trace where the live pin of the IEC connector goes. It shoud go to the fuse and then via interference suppression choke winding to the AC side of a bridge rectifier. The neutral side will do much the same without the fuse. The DC output of the bridge goes to a pair of 200 volt electrolytes that are in series when the voltage selector is set at 230v. These are the caps that people warn you to discharge.

After that it gets more complex, but the input circutry of any switchmode PSU really is as simple as I have described and it's well worth doing some cold tests.

[Bernard Peek]

ITX warehouse have possible replacements. A 12v power brick together with an adapter that plugs into the motherboard's 20/24-pin power socket.

[John Rumm]

I have a Ideq small form factor machine here that I was probably going to scrap - the PSU on that may well fit in your case. If you measure the dimensions of yours, I can let you know if it will fit.

As a check, to make sure it really is the PSU, disconnect it from the motherboard, and force it to startup on its own by briefly connecting the green wire in the motherboard connector to one of the black wires using a offcut of wire etc.

Reasonably good I would have thought.

[D.M. Procida]

You were right! There is a cunningly-placed vertical fuse, sheathed in heat-shrink plastic. Weirdly, the fuse seems to rotate on its axis, so I don't know what kind of fitting it has.

Sadly (or not) the fuse hasn't blown; there's continuity across it, so that doesn't appear to be the issue.

I shouldn't expect to find DC continuity across the bridge, should I?

Daniele

[D.M. Procida]

That's kind. The specs are:

Internal Switching Power Supply: Model No.: ENP-2222D Dimensions: (mm) 150 (L) x 82 (w) x 65 (H) Intput : 200-240V~ / 3A 50Hz Output : +3.3V 17A

+5V 13A +12V 16A

-5V 0.3A

-12V 0.3A

+5V 2A Total : 220.00W

But it's a slightly odd a shape - as in: .

Daniele

[Bob Eager]

That doesn't look like a 'standard' Mini-ITX PSU, unfortunately.

I'd go for a pico-PSU and an external power brick. Easy fix for Daniele, I would hope!

[Bob Eager]

I suggested that too, but a lot of those are limited in what they can deliver. Depends on the drives, etc. although the Morex cases generally only support laptop-style optical drives and one hard drive.

[Graham.]

No. Your meter will have a diode test range and the reading is actually in volts. Across any adjacent pins on the bridge rectifier you will see a reading in the order of 0.6v in one direction and considerably higher in the other.

But as the fuse is intact I don't think that will be your problem, as if any diode(s) in the bridge went short circuit it would take out the fuse, (or the printed track connecting it).

Is there a low resistance connection from the middle two pins of the bridge to the L & N pins of the IEC mains socket?

[John Rumm]

approx 142 x 80 x 55

Yup - same spec...

This one is a more regular cuboid - but a tad smaller as above

[Johann Klammer]

How did you test it? Did you plug in a different PSU? If you do an offline test, you have to pull the PS_ON pin(14) low briefly to turn it on. But 5V standby(9) should be available as soon as plugged in. Pinout:

the whole box just does not work anymore, it may as well be the mainboard.

[D.M. Procida]

It's part of the resistance range, and shows around 670 (Ohms, I presumed) in one direction, and an open circuit in the other.

This is across any two pins, except the two in the middle (the rectifier is a square block, not discrete components).

In one direction only, and it's about 2 Ohms for one pin and about 10 in the other.

I actually picked up a second hand signal generator and oscilloscope recently - would they be useful in this?

Daniele

[Jules Richardson]

If you're serious about fixing it, then the following is a useful resource:

think that a meter's normally all you need though when it comes to completely dead PSUs; something will likely test as shorted or open when it shouldn't be etc.

Think about the simple stuff first - Does the fan run? Does it twitch at all when the machine's powered up? Do you get any voltage at all on the various outputs? Are you sure that the machine's power button (and related wires) are OK? Are you sure that the motherboard isn't toast (and the PSU is seeing a short circuit and shutting down)?

cheers

Jules

[D.M. Procida]

Does yours have a model number on it, so I can compare the mounting points etc?

Thanks,

Daniele