My computer started turning off automatically every 5 seconds. I disconnected the power supply, shorted the switch contacts so it'd come on, then measured the voltages. Those rated at +12V read 12.08; that rated at -12 reads -11.62; that rated at 5.08 reads 5.13. An unidentified white reads 1.18; an unidentified gray reads 4.92. I suspect they're all within range, at least without serving a load. When they're plugged in they come up to rated voltage then drop to zero, then they come back up again.

Any idea what the white or gray wires are for? They connect to pins in the motherboard's jack.

12V looks OK; 5V looks low; I wouldn't worry about -12V, as I don't think that's used. I'd expect -5V line (for historical RS232) unless it's been dropped.

I get the feeling this PSU is ancient, because there's no 3.3V line, and 3.3V would have more than 1 wire on any modern PC. There was a (blue?) 'power good' line in the early days, which was switched high (5V) or low depending on the power supply state. You could see how that behaves.

So I reckon if the power supply is ancient, it is in trouble. Try loading the lines, as some may need a load. Read the voltages again then. I'd like 1 Amp on the 5V (5 ohms) and something across the white line - 22 ohms?. The minimum supply current was 500mA, and the lighter current lines drag down without blowing.

The early PCs were built with heavy current TTL and they were clunky. Today's stuff is ever so sophisticated by comparison.

The motherboard has support for serial and parallel! (also USB3 and DisplayPort). Only the pin headers on the motherboard are there for them, not the outlets.

The Blue is -12. The white and gray are unremarked in the docs and the label of the PS. It's a Lite-on PS 4241-01.

RandomTroll,

To resolve this you really need to borrow (or buy and return at Amazon or other) a functioning PSU and install it temporarily.

If the replacement works without errors, then your existing PSU is faulty.

do you mean this: https://m.media-amazon.com/images/I/...AC_SL1500_.jpg ?
that is more than 10 years old low end PSU. I would definitely try to replace it.

pan64,

It is more likely to be an OEM one from FSP, but either way, they are both cheap old units which have probably seen better days.

https://support.lenovo.com/gb/en/vid...-tower-desktop

See attached screenshots from above link.

Attached Thumbnails

   

Excellent idea! I paid $41 for this computer. I should buy a new power supply for $70.

That's it!

I assume it's original equipment: what makes you think the rest of the computer has outlasted the power supply? In my experience the PS is the hardiest component.


Which describes the computer.

Not including the user, hopefully!

Hope on: it describes me, too.

That's why you could buy it for $41. By the way, you can buy my old car for a few hundred dollars, you just have to come here, pick it up, fix it and use it. That's it. That's it?


What you explained means the PSU is over. Usually (and especially in low end devices) the capacitors will give up sooner or later. But you are right, there can be a problem with any other parts too. Anyway, if you want you can try to replace that PSU to see if that helps at all.

Generally, there's no 'use-by' date for electronics. Heat-cycling is the accepted method of ageing electronics. But what that does is pick off the ones that nearly failed QC tests, but passed. My RazPi SoC is an example: It was specified @1.5GHz, but you could overclock them nearly all to 2.150GHz. I can't clock mine past 1.8GHz. I expect it to die one day, but there's no telling when.

Electrolytics as used in power supplies, are squeezed on packet size, capacity & then often soldered too close to the packet. Soldering expands the legs, which contract in the board, stressing the device structure. They do die. OTOH, I have seen 70 year old electrolytics working well. Switched Mode electrolytics and commutation capacitors live a hard life and often exceed their AC rating (a little known capacitor spec).

Generally, though, there's no age limit on semiconductors, nor any way to tell which bit is going to die next. I could have made a fortune if there was.

This means that this PSU is dead.
Replacement may be difficult or expensive, because this PSU without +3,3 V line is a proprietory one and not a standard ATX PSU: https://en.wikipedia.org/wiki/ATX (see chapter "Power supply")

You don't write something about the affected computer (model, photos that show PSU in case and PSU plugs to mainboard).

In some cases e. g. some "Lenovo Thinkstation", replacement of original proprietory PSU with a standard ATX PSU is possible. Reqirements:

• A standard ATX PSU fits into place of original proprietory PSU.
• A standard ATX PSU provides all lines with same or more power as lines provided by original proprietory PSU.
• Adapter cables from ATX plugs at PSU to proprietory PSU plugs on mainboard are available or can be soldered.

No, see link to ATX PSU above. RS232 is not historical. It's currently provided by some mainboards, especially "full size" ATX mainboards. Only some parallel interfaces (IDE, SCSI, Parallelport, MIDI, Game, …) has been dropped over the years.

What about it means the PS is over? The PS is as old as every other component. Usually they are hardier. It tests properly out-of-circuit (but not under load). I took it apart: everything looks okay, including the capacitors.

I don't need to be told that. I could do the same for every component.

They look good to me.


What does?


It's a Lite-on PS-4241-01, a common ATX PS, for sale many places. Lite-on doesn't seems to make them anymore. eBay has a used for $14. Then again I can buy a used M93P for $30.


Thinkcentre M93P 10A8.


I can replace it. I was hoping for help deciding whether it is defective so as to avoid unnecessary purchases.

I've tested further: even when I remove the CPU it reboots. I took the motherboard out, put it on a wood table, plugged in: it reboots. The peak current drawn by the PS is .6 amps (@120V = 72 watts). It's rated at 240 watts. Only the first boot draws .6; subsequent draw .1, consistent with the capacitors working.

My experience is the opposite, except with Dells that haven't yet reached 12-15 years of age. Lots of dubious-named electrolytics have gone into PC PSUs where their origin cannot be determined without removal. I have a sizeable bunch of old PSUs still working only because I bothered to replace caps that may or may not have been determined bad by just seeing leakage or bulging.

PSU have "high power" electrolytic capacitors, see about life cycle here: https://en.wikipedia.org/wiki/Electrolytic_capacitor