Re: Looking for a 1998 era Sun VME computer. Photo attached.

On 01/19/2011 08:15 PM, William Merrill wrote:
> Thanks Simon.  Our techs have discussed the fact that electrolytic capacitor
> sometimes dry-out with age, but nobody mentioned a wholesale replacement as a
> fix.

You might want to take a defektive power supply, remove all the 
electrolytic capacitors one at a time and measure their remaining 
capacity (using the proper equipment). If dry caps are a problem, at 
least some of them should be at less than 50% of the capacity printed on 
them. Replace those.

Lately I had to replace capacitors in the power supply of 2 DSL modems, 
in one it was the big one on the input side (rated 47uF/400V) and 
obviously bad (bulging top), in the other one it was a tiny cap 
(10uF/25V or so) next to the controller IC (UC3842). The latter fault 
was a pain, the power supply ran fine while warm but would not start 
while cold. Warm it up a bit and it started and ran until the next power 
failure.


> Other users of this
> type of computer have warned us that though the computer runs on 28 VDC, there
> are other signals flowing in the power supply pins which are poorly understood.

Probably control signals for the LEDs, presense detection, temperature 
sensors, power-on-control, standby voltage.

  Gerrit