Failed computer PSU?
 

Recent history:

Increasing failed boots; fans spin up and nothing else happens, so hit the power switch and try again (and again sometimes)

Today:

1. Pressed power switch of PC
2. Nada
3. Popped the case off the side of the PC
4. Could see power LED illuminated on mobo
5. Unplugged mains power lead
6. Waited for LED to extinguish some 15 or so seconds later
7. Unplugged 20+4 (it's two plugs) ATX power lead from mobo
8. Shorted pin for green wire with the adjacent black wire (I understand that any of the black wires can be used)
9. Checked power switch on PSU itself was off
10. Plugged mains cable back in and switch on plug
11. Pressed power switch on PSU
12. Observed fan made a half hearted attempt to spin up, and then stopped
13. Repeated ad nauseam

To me it's pretty conclusive that the PSU 12v supply has been failing and has now gone below the minimum threshold to allow the PC to boot..

Likely correct, before I buy another PSU?

Either that or something is overloading it and causes it to trip out. You could try unplugging bits to see if if fires up.

Half an hour ago during my lunch break I removed the PSU entirely (physically, including ALL leads) from the PC. The fan symptoms are the same.

Ho hum.
Time to get the wallet out!

Cheers,
XV

Have you checked the wiring from the power switch to the motherboard? Worth unplugging this and reseating it.

Also worth reseating the CPU and RAM - can sometimes work their way loose and cause random faults.

Thanks anyway but per previous post it has now been removed entirely from the PC and confirmed faulty.

Test in situ
 

PSUs for ATX boards will shut themselves down if they're disconnected from the board.

Not if this article is correct, which is what I did per my original post and when removed:

modtown - article - Powering an ATX PSU Without a Motherboard - if it ain't broke - mod it!

One of these has been ordered to replace it, in the process giving me some future proofing oomph too compared to the original 550w (rated but I doubt even that) unit that has failed.

Coincidentally, one of my PSU's failed last night, but in a way that assisted analysis: it went flashbangsmoke, as would be expected of any cartoon PSU. Swapped it out with an ATX 2.2-spec unit rather than the 2.0-spec (and incidentally noted a 750W/820W unit was the most efficient at the power this box normally consumes). Took me a while to realise the 8-pin ATX-12V connector slides apart to form two 4-pin units. Also looked longingly at the two spare PCI-e 6+2 feeds: my video card doesn't need one, but now I've got these connectors mocking me. This could be an expensive PSU by the time I've fnished. I've got to open the case anyway, to locate and destroy the bright blue light in the PSU.

I wish mine had gone flashbangsmoke, bf! At least I would have had some entertainment value.

Mentioning "cartoon" PSUs, my PC is a custom build jobbie from MESH with three internal HDDs, two optical drives, and three cooling fans in terms of the main power consumers other than mobo and associated gubbins. One of the few things I did not specify by name was the PSU and I was surprised when it came with a HEC 550w tiddler. Not only that, but when I decided to take it apart yesterday I was horrified at the cheap and cheerful innards. Truly ghastly, actually, and at complete odds with the high quality components that make up the rest of the build. It has a very noddy circuit board cluttered with cheapy-cheap components and not the slightest air of sophistication. I would be amazed if MESH paid even a tenner for it and am even more surprised (Google confirms I am not alone with failure) that they trust their name with it.

It is clear from the link and other advice was shared with me that the Antec replacement is going to be in a different league :)

HEC: some people love 'em, some hate 'em.

As long as you get one that isn't OEM by HEC, of course :}.

I don't actually mind if it is OEM from HEC (and one of the photos in the link I shared shows that it is likely come from China), so long as it is built to the physical standards and has the electrical performance that Antec appear well known for :)

New Antec "Truepower New" 750w PSU now fitted, so what's it like?

Being ATX it was as completely plug and play as I hoped for, but it is also in a difference league to the HEC. In this case at least it was certainly therefore a matter of "you get what you pay for".

• Visually higher grade cabling
• A circuit board that actually looks like it has been designed rather than cobbled together by a five year old
• Discrete SATA and Molex runs from separate supplies rather than daisy chaining the former off the latter with splitters and short converter cables on the HEC. Whilst this obviously worked, it is noddy and against the purist in me
• The presence of net cable sheaths to protect and group each run
• Molex connectors of a high density plastic rather than something one grade up from a polythene bag
• A 24pin ATX connector that sleeved in to its mate with a nice tactile feel and positive "click" rather than wiggle-wiggle-I-think-it's-connected
• Near silent fan operation
• Oodles of expansion (both in terms of 750w rated oomph that I actually believe vs 550w that I'm not convinced about and with three spare 12v rails for which cables to connect to just about any component going have been supplied)
• It just looks and feels classy and I can well believe all the high quality tech attributes explained in the review I linked to

Happy camper, and yes, a case of PSU failure was correctly diagnosed!