Help with ICL power supply fault (Farnell SMPS)

[Tony Duell]

> > > Scoping tbings in there would sure be informative.
> >
> > The prolem is that if this is like most small SMPSUs, then almost all t=
> he
> > 'interesting' circuitry (oscillator, etc) is on the mains side of the
> > isolation barrier. And therefore you can't just connect a 'scope to it,
> > not unless you like shorting out the mains via one of the rectifier
> > diodes and the earth (ground) lead of the 'scope.
> 
> This is true,  though at the time I wrote that I was thinking about scopi=
> ng=20
> the outputs.

Most of the tiem, if the outputs are pulsing, they're doing so quite 
slowly (~1Hz), so a non-storage 'scope won't tell you anything more than 
an analouge meter. 

I suppose it's possible you might see a higher-than-normal voltage spike 
on one of the outputs which will trip the crowbar, but I think it would 
be very easy to miss that. 

-tony