Info on testing vintage power supplies

Alan Perry aperry at
Sat Sep 7 20:43:45 CDT 2019

On 9/2/19 9:56 AM, Tony Duell wrote:
> 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.

The power supplies that I had been looking at were the two in the SMD 
disk cabinet. Still haven't tried powering them up.

Today I opened the 3/260 cabinet. There was a nest made by some rodent 
on top of its power supply. It was composed of shredded material that 
went down into the power supply through the holes in its cover. From the 
surface rust, it looks like there was moisture in the nest.

What should I do to the power supply before trying to power it up?


More information about the cctech mailing list