Transformer Fault in a PSU?

[wrcooke at wrcooke.net]

> On January 12, 2020 at 3:10 PM Rob Jarratt via cctalk <cctalk at classiccmp.org> wrote:
>
> 
> Can anyone help with the following questions:
> 
I have some experience with similar stuff, but not a lot.  I will give possible answers as I understand them below.  Perhaps someone with more experience will come along later.


> 
> Does the fact that one winding is operated in flyback mode have any bearingon the ringing test?

It should not have any effect.  A winding is a winding, regardless how it's hooked to whatever external circuit.  Once removed, the external circuit doesn't matter.

> Can a transformer fail with a bad smell with no outward sign of damage?
Melted enamel insulation on a winding, shorting the winding, will cause some smell and a failed transformer without any outward sign.  One of the main uses of a ringdown test is to find shorted turns, since they aren't otherwise observable.  The internal resistance of the winding will be a tiny bit lower, but generally not enough to tell by measurement.  A shorted winding causes it to NOT ring because all the energy gets used up quickly in the shorted winding (as heat.)

> Can this transformer be replaced (see picture in blog)? - I suspect notunless I find a donor PSU.

You may be able to rewind it.  That would be an "fun" exercise.  The transformer "may" be a standard part, but I doubt it.  And what was sold as standard 20 or so years ago isn't likely to still be available new.  The core, however, may still be available.  But you already have a core.  And, you would most likely need to disassemble the current one anyway to find out the number of turns per winding as well as the size of wire used.

> Where should I look for a possible cause of the transformer to fail (ifindeed it has failed?).
> 
> 
> I have posted more details here:https://robs-old-computers.com/2020/01/12/possible-cause-of-vaxmate-h7270-psu-failure/
> 
> 
> Thanks
> 
> 
> Rob

Hope this is at least some help.  Sorry I can't give more definitive information.

Will

"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." --  Antoine de Saint-Exupery


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