Info on testing vintage power supplies

Tony Duell ard.p850ug1 at
Mon Sep 2 11:56:25 CDT 2019

On Mon, Sep 2, 2019 at 5:35 PM Alan Perry via cctech
<cctech at> wrote:
> Can anyone here provide a pointer to info on testing vintage power
> supplies? Search results on the web may eventually lead to the kind of
> info that I am looking for, but I have to get through too many pages of
> modern PC power supplies first.
> Specifically, I will be testing the power supplies in my Sun 3/260,
> which has 24V, 12V and 5V. I am wondering things like what is suitable
> loads and do I need to put a load on all three or can I test them one at
> a time and what I haven't thought of with regards to testing them.

With most classic computer switch mode PSUs (which the one in a
Sun 3/260 is), you need to load the main output. The other outputs don't
_need_ loads, but it doesn't hurt to have them). For 99% of classic computer
supples (and true for the Sun 3/260) the main output is the +5V one.

I'd try to draw perhaps 5A from that. So a 6V car bulb of 30-odd watts. A
6V car headlamp bulb, for example. It's not critical Have that connected
between the +5V output and ground (the 0V rail of the machine, not
necessarily mains ground) for all tests on the supply. In other words,
connect up the bulb, power up (the bulb should light), then measure the
voltage between each output of the supply and ground.


More information about the cctech mailing list