decserver 700-16 fan problem

[jlang]

I have a decserver 700 that I just noticed was dead. put on bench powers up. tftp loads. basically works.... except the fan.
first thought fan bad. not an uncommon problem.... Nope runs on bench supply. probe pins on PS. no joy 0 volts.
This thing is a line operated SMPS, so before I probe too deeply and let out the magic smoke (or worse) Does anybody have any details on the guts of this supply?
Looks like the PS has some fan speed control stuff that's likely the problem.

 

[MauriceH]

Could be a heat sensor and then it will only run if internal heat becomes at certain level.
Mostly a NTC somewhere on a heat sink.

Test with a heatgun to quickly heat up the internals and see if than fan will run.

Otherwise just follow the PCB-wiring and see if it ends on a switching transistor, that way you know it is heat switching
or not.

 

[jlang]

final resolution: Re capped the supply. Cleaned with a compound "known to the state of California to be a carcinogen" Everything is back to proper operation.
total cost: $10