Transformer Fault in a PSU?

Jon Elson elson at
Sun Jan 12 15:49:09 CST 2020

On 01/12/2020 03:10 PM, Rob Jarratt via cctalk wrote:
> The PSU in my VAXmate failed recently and I think I have found a problem
> with one of the windings on the transformer not ringing when I test it with
> a ringing tester. The technical description of the VAXmate says that one
> winding is operated in flyback mode and I wonder if that has any bearing on
> the ringing test. Also, one of the pins appears not to be connected to
> anything else, so possibly a broken (melted?) wire.
The un-connected pin COULD be an electrostatic shield.  If 
so, it would read like what you get.
> Can anyone help with the following questions:
> Does the fact that one winding is operated in flyback mode have any bearing
> on the ringing test?
> Can a transformer fail with a bad smell with no outward sign of damage?
Absolutely.  But, are you sure the smell came from the 
transformer? Caps are notorious
for being more unreliable.
> Can this transformer be replaced (see picture in blog)? - I suspect not
> unless I find a donor PSU.
It is almost certainly a custom unit.  It is remotely 
possible some similar power supply might use
a close-enough transformer.


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