VAX 4000-500 PSU Overload?

[Dave Wade]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Robert
> Jarratt
> Sent: 19 December 2015 19:19
> To: 'General Discussion: On-Topic and Off-Topic Posts'
> <cctalk at classiccmp.org>
> Subject: RE: VAX 4000-500 PSU Overload?
> 
> 
> 
> > -----Original Message-----
> > From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Dave
> > Wade
> > Sent: 19 December 2015 18:32
> > To: 'General Discussion: On-Topic and Off-Topic Posts'
> > Subject: RE: VAX 4000-500 PSU Overload?
> >
> >
> >
> >
> > Seeing as it already seems to have over current sensing, I guess it
> > has
> some
> > small resistors in there so perhaps it is possible to measure the
current.
> I
> > notices one looks like this:-
> >
> > http://uk.farnell.com/welwyn/oar1-r020fi/resistor-1-0r020/dp/1200359
> >
> 
> 
> Ah! So that is what those things are! I definitely think this one is
detecting
> something wrong and shutting down the 12V side. I have just been doing
> some tests with a dummy load and the 12V side will come up and then go
> down a few moments later, sometimes it will stay up, it seems a bit
random.

I wonder if the voltage level detection thinks its out of spec, rather than
the over current parts. These PSUs afre exceedingly complex...

> Presumably then, there is something wrong with the overcurrent detection.
> 
> I will have to look into how you test these, or perhaps just replace them
and
> see what happens.
> 

I can't see the resistors themselves being the problem. Perhaps re-soldering
them 


> Regards
> 
> Rob

Dave
G4UGM