Hi there, 

As electronic tecnician I would recomend following

disassemble the psu
clean, blow, vacuum all dust,bugs and ... from the unit
examine the solder side of the PCB board, carefully examine all solder
drops to see if there are any cracks, very very fine cracks are trouble
to.
re-solder the cracked solder spots

If there are any signs of heating, dark brown or discolored areas on the
PCB examine and resolder.

Well, at last take very good look at all the capacitors, if capacitor
looks bulgy, cracked at the top or leaky, replace it. Best with low+z,
higer voltage, higher temperature rated (105degc in stead of 85degc)

This is what fixes 99% of broken TV sets, specially PSU problems.


Thordur


NetBSD Bob wrote:
> 
> > My VaxStation 3100m38's power supply is failing. It will run for about an
> > hour or two before turning off. Cycling the power turns it back on. My
> > question is does anyone have a spare one of these power supply's that they
> > would be willing to sell to me?
> > Thanks.
> 
> Things to try with power supplies that work, but don't seem to last.
> 
> Symptom... power supply dies with time
> 
> Cause...   most likely due to heating internally in the power supply
>            around critical parts, causing shutdown of the supply.
> 
> Fix...     completely disassemble the chassis down to bare metal cases
>            and boards and remove the power supply.  Blow/brush out dust
>            bunnies and residual dirt.  Reassemble and retry.  TAKE CARE
>            TO ASSESS THAT ALL FANS ARE PROPERLY RUNNING.  Replace any
>            fans that are slow to start or making any dragging sounds
>            or that are not spinning up.
> 
> Good LUck
> 
> Bob