HP 9845B Power Supply Unit

tony duell ard at p850ug1.demon.co.uk
Mon Apr 18 06:26:47 CDT 2016

> Hi,
> a recently acquired HP 9845B desktop computer came with a literally broken
> power supply unit.

The HP9845B PSU is very complicated, IIRC it's actually 2 SMPUs and has 
various switching regulators on some of the outputs too. It is also painful
to test as you can't get to it when it is plugged into the machine.

> One of the ferrite core transformers has a broken core. The lower, U-shaped
> core part is broken in the middle into two parts.  Both parts are still
> there, rattling around in the coil part / transformer fixture. I do not
> think that I could find a new matching core.

My guess is that this is one of the main chopper transformers. They are
going to be somewhat critical I think.

> I am not sure of the magneto-electrical requirements and would like to hear
> about your experience or opinions:
> - should I glue the broken ferrite core with e.g. super-glue or epoxy (of
> course with ideally zero or minimum gap between the halves) ?

If it is a clean break then this is probably the best solution as it will have 
the least effect on the magnetic properties of the core. I think a 'thin'
adhesive of the iso-cyano acryllic hydro-copolymerising type (aka
'superglue') would be better than an epoxy resin here.

> - would it work or are there better ways to fix broken ferrite cores (e.g.
> adding a steel wire insert or something like that?)

I would not try to add any other metals, which will have an effect on the 
magentic properties of the core, may increase losses, and nasty things
like that.


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