View Full Version : Dead power supply Olivetti M24 ?

September 24th, 2017, 12:53 PM
So I got this Olivetti M24 and after cleaning it out (there was about a kilo of dust inside) I powered it up and...nothing blew..yes!
Hmm but I just heard the fan going, that is not a good sign.

Opened it up and measured the big 5V connector and it registered as 0.3V.
In my opinion the power supply is probably dead but what do the experts here think ?
Ow I did measure it with everything but the drives still connected.

September 24th, 2017, 02:11 PM
First of all, you have a nice schematic of the not-very-complicated PSU on PDF page 26, so repair, if needed, is straightforward.


But have you disconnected the power supply from the motherboard before checking the voltages? You could have a simple short fault on the motherboard.

September 24th, 2017, 09:39 PM
That power supply can not work without load. So disconnecting it and measuring then is not a good idea. You may damage it without load.

The 2nd difficult on this PSU is that inside the PSU box you have two boards, linked just by two wires with high voltage on them. These cables are too short to lay both boards side by side to check them, so you need fist longer replacement cables to link them. And don't forget the electric load on 5v and 12v when testing.

It's not fun debugging and fixing this power supply.

September 25th, 2017, 07:54 AM
I doubt that you'll damage it without a load. Hook a hard drive or two to it as a load if you want.

The point is that the PSU may be perfectly fine and that there is a component on the motherboard that is causing a problem.

September 25th, 2017, 11:31 AM
Remember that I used to work there and I still remember the load-resistors we had to use to debug these powersupplys.

September 25th, 2017, 11:44 AM
So you're recommending that the OP bin the PSU? Without even checking to see if the fault lies in the motherboard?

I'm having difficulty getting the drift of your advice.

September 25th, 2017, 12:23 PM
No, I don't. I only remember everybody to be carefull with this PSU. It's a very old switching PSU and these ones need load to run. I also think it's not short circuit resistant, so avoid shorting. If one wants to test, then only with load-resistors (1,5 Ohm 20 Watts or something like that on 5V) and don't touch them, they are getting hot if the PSU is Ok. When debugging it, then screw the boards of the PSU on a wooden board and take a longer connection cable to link them. And be carefull, on that cable you have painfull 480V or sonething like that (220/230V model, for 110V type I don't know). Fixing this PSU means you need to know what you are doing. Study the circuit diagram first to know what you can expect to find and where not touch it.

September 25th, 2017, 12:44 PM
A cheaper alternative I use with DEC supplies are 6V motorcycle bulbs and 12V car bulbs in various Wattages in a series/parallel combination for the voltage rail concerned. They are much cheaper than high power dummy load resistors (if you don't have any around) and are generally available in a high street motor factor shop or garage.