On Fri, 19 Feb 2016 22:44:08 +0100, Dimitrij Klingbeil wrote:

Are you sure that you have not mixed up the windings? Maybe the two 1.8V
windings are actually the 2 symmetrical "innermost" ones, the 3V ones
are the "medium" ones and the 15V are the "outermost" windings? Your
measured winding voltage ratios "1.8:3.0:13.0 volts" and the schematic
output voltage ratios "6.7:13.4:60.7 volts" (I've added a little
compensation for 0.7V silicon diodes) are (from a purely ratiometric
point of view) not very far away from each other. In fact they are so
close that the differences between the smaller ones can be easily
explained by your measurement errors (how accurate was that 0.8V
measurement anyway?) and the possibly intended uneven loading of the
power rails in the scope.

I follow what you're saying, Dimitrij, but for that to be the case, the
tranformer's internal wiring would have to be twisted and I can't see why
they would do that. Admittedly the ground pin is in 'real life' at the
far end of pinouts rather than the centre, but... well, I don't know. If
you're right you must be some kind of genius, that's all I can say.

So, considering the winding connections slightly rearranged, the
transformer looks just fine to me.

But once you have it out and disconnected, please make another test:
apply ca. 15V RMS to the 12.7V winding (to the one where you measured
3V) instead of to the primary. And check if any isolation looks like
breaking down. Note that the 15V value contains some compensation for
the fact that the power supply uses inductors after the rectifiers (and
therefore the normal winding voltage is higher than the normal output
voltage). That would load the transformer close to its normal condition
and any breakdown should become apparent.

OK, you're the boss! I'll carry out that investigation tomorrow and
report back. Maybe I can work out if the internal taps are out of
sequence compared to the schematic by measuring the DC resistance of the
winding at the various taps and... well you get what I mean. Intriguing
idea certainly deserves to be fully explored. Many thanks.