Dead Champ Mains transformer?

[JB]

Got an old Silver Face Champ to repair for a friend.  Export version, 200/250V.  Blows mains fuse with no valves in.  Fuse was a 2A slow blow, not the .5A slow blow listed on the back plate.  That probably hasn't helped. 

I think it has a partially shorted B+ winding.  I measure 210 ohms across the winding (red pair) but the centre tap (red/yellow) measures 180 ohms to one leg and 30 ohms to the other. 

However, there were three wires on the earth lug - one half of the 6.3V winding (green), the B+ centre tap (red/yellow) and also an orange wire.  This orange isn't shown on any schematics or layouts I can find but googling Champ chassis pics shows it in some of the images.

The orange masures 24 ohms to the red/yellow and 204/15 to the two reds.

Any idea what that tap is and, either way, am I right in thinking I've got a damaged B+ winding?

Edit: Just checked the spec for a hammond drop in replacement and they show B+ winding resistance as 334 Ohms, so one half of this one measuring 180 ohms is about right.  Other half must have some shorted turns.

[2deaf]

Orange is probably the same as what I am calling pink and it is connected to that copper flux band around the outside of the transformer.

[JB]

I guess salmon pink is a bit orange!  I think you're probably right.  And I've found one replacement that has an orange lead connected to "case ground".  However I can't measure any resistance from orange to the copper band.  But if it is that then there really shouldn't be any continuity to any part of the B+ winding.   

I think this transformer is going in the bin.

[2deaf]

However I can't measure any resistance from orange to the copper band.  But if it is that then there really shouldn't be any continuity to any part of the B+ winding.

With my pink lifted from ground, there is no continuity to the copper band, either.  The copper band does have continuity to ground even with all transformer leads disconnected.  More importantly, my pink has no continuity to any other lead.

[JB]

Ah, that's interesting.  Just tried that on this one - yes, continuity from the band to chassis but not the orange lead.  But also from orange to the B+ winding.  And of course orange was connected to chassis so was taking down part of the B+ winding and popping the fuse.

Thanks for your help, I'll get a replacement on order.

JB

[sluckey]

If you measured resistance between orange and reds with the orange still connected to chassis, then you should have continuity because the red/yel is also connected to chassis. Disconnect the orange and the red/yel from chassis to get a true reading.

[JB]

Sorry, should have said all my readings were with the transformer wires lifted from ground.  So I'm getting continuity to orange, which I shouldn't, and the red's centre tap isn't in the centre anymore - 180 ohms to one leg, 30 to the other.  So sounds like some insulation has melted inside this one.