Old Power Supplies, revisited

From: Gary Hildebrand <ghldbrd_at_ccp.com>
Date: Sat Apr 27 22:40:50 2002

Louis Schulman wrote:
>
> I am putting my SWTPc 6800 back together, after complete disassembly
> for cleaning. So, on to testing the power supply.
>
> It works! But here's the question, which I know has been discussed
> before with respect to S-100 machines.
>
> The power supply is a big transformer with one really big (91,000 ufd)
> capacitor, and the usual rectifier stuff, etc. The documents call for
> 7-8 volts unregulated, along with + and - 12V.
>
> I am getting something like 9.3 V, and + and - 14.3 V. Are these
> voltages too high? Of course, on the SS-50 and SS-30 cards there are
> voltage regulators, but I don't want to cause any damage. This thing
> probably hasn't been powered up in 25 years.
>
> How can I check the capacitor function without an oscilloscope or other
> fancy equipment? Should I worry about "reforming" the capacitor?
>
> Thoughts appreciated.
>
> Louis


Shouldn't be a problem, as S100 cards have onboard regulators to get +5,
and +/-12. Only problem there is that the regulator transistor will be
dissapating a bit more power, so have a fan on the card cage if
possible. The heatsink should run warm to the touch, and if it it is
too hot to comfortablly hold for several seconds, then you may be in
trouble. Any excess heat means a premature death for solid state
electronics.

You might look at the cards and inspect the regulator circuitry. a
darkening of the pcb underneat the heatskink is normal, but if the
traces seemed to be crispy crittered, ya got problems, or will have
probs very soon.

Gary Hildebrand
ST. Joseph, MO
Received on Sat Apr 27 2002 - 22:40:50 BST