Power Supply jumpers

I've got a 115V power supply that outputs 12VDC. This unit was pulled from a machine that was built in Japan and it's possible it was custom built for this device. I can't find any identifying information about the power supply, to look up documentation.

I plugged it in and started testing the output side to see what I'd get. There are 4 terminal posts on the DC output. Terminals 2 and 3 are jumpered together -- making me think the configuration is: T1 (+12V), T2 (GND), T3 (GND), T4 (+12V). When I put my multimeter on Terminals 1 & 2 I get 12V. When I put it on 3 & 4 I get -12V. Obviously, reversing the leads on my multimeter makes it +12V.

So the question I've got is: why are 3&4 jumpered together? I would think that would only be done if they were ground. But I only get +12V on the multimeter if I treat terminal post #3 as positive, not ground.

Do you get 24V measuring from 1 to 4? This would be great for an analog supply, +/-12 for op amps, ADCs, DACs, was always my preferred way to power things, keep the signal at DC level vs running it thru caps all the time.

Ah - yes, I do get 24V.

I've got 4 other power supplies from this unit, some rated 12V, some 24V, some 5V. It was a film scanner, with 13 stepper motors and probably twice as many sensors in it (plus several custom PCBs that I've removed). The Steppers are all 24V, some of the sensors are 12v, some are 5V. I intend to reuse as much of this as possible, since my new setup will use 6 of the original motors and a bunch of the sensors.

Good to know I have the flexibility to use the 12V power supply as 24V if necessary.


+/-12V supply for all the opamps and analog circuitry, at a guess. Originally opamps were always powered from +/-15V or +/-12V. Then low voltage opamps started to make an appearance.