Help with ICL power supply fault (Farnell SMPS)

Roy J. Tellason rtellason at
Wed Apr 9 17:05:16 CDT 2008

On Wednesday 09 April 2008 17:19, Tony Duell wrote:
> > Hi,
> >
> > I have an ICL PC2 CP/M box (like this:
> > which has a
> > faulty PSU, I am hoping someone here can advise me.
> >
> > The PSU is a Farnell N100/F4190 SMPS, looks like a high quality unit
> > with nice screw terminals for mains in and DC out.
> >
> > When fired up with 240V AC and a dummy load the output voltages are:
> >
> > 12V output=1.1V
> > 5V output=2.3V
> > -12V output=-5.9V
> The first thing that 'bothers' me is that the 12V output is lower than
> the 5V one. If this was a simple regulation fault, I'd expect all outputs
> to track.

I've expected that too,  in the past,  and it hasn't been the case at least 

> I think it's reasonable to asusme the chopper is working (otherwise you'd
> get no outputs at all). Does it seem to be running continuously, or do
> you get the 'tweet tweet tweet' of a PSU that's starting, detecting a
> fault, shutting down, and repearing?

Scoping tbings in there would sure be informative.

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