Agilent E3649A power supply oddness - looking for advice

[TheSteve]

I bought an Agilent E3649A dual output supply that had a broken VFD as it was a great deal and seemed like an easy repair(yeah right).

I sourced a VFD from a used supply, installed it, and the unit powers on without error.
It can also supply the rated voltage/current from each output.

But, there is always a but isn't there?

When you draw current from the supply it makes a popping/motorboat type sound - kind of like you'd get if connected a AA battery to a speaker coil over and over.
Both outputs make this noise, yet they both sound a little bit different.
I am quite sure the noise is from the transformer.
At first I thought maybe the transformer was damaged but there is no leakage that I can detect between any of the windings(I have only checked at DC, not higher voltage).

And here is the other oddity - when the first output is heavily loaded the second output will drop by a few millivolts. If you load the second output the first output does not change.
The two supplies should be fully isolated so to me it seems the problem is some sort of leakage between them.
The lower board has all of the regulation circuitry in the supply, there are isolated sections for each supply and I cannot measure any resistance between them. The common connection point is the controller board, there is nothing obvious wrong with it though.

So has anyone ever seen anything similar to this?

[sean0118]

I *think* that type of sound is commonly caused by a short between loops of the same winding. As in, the enamel of the wire has broken down. I'm not sure though and I don't know the procedure to test for it. 

[HighVoltage]

You should test the transformer with a higher than normal working voltage and look for leakage. To me this looks like a transformer problem. Some winding problems only show up at higher voltages and higher loads.

[TheSteve]

Having thought about it more it does seem likely it is a transformer issue. I assume the supply took a hard drop/blow which broke the VFD, at the same time perhaps some coils shorted on the transformer.
Kind of a hard one to fix.

[dom0]

In rare cases this can be fixed with low viscosity impregnating resin. But don't get your hopes up...

[feedback.loop]

One can always rewind a transformer. This might be quite tedious, but it is a low-tech thing, and is doable with some patience.

[IanJ]

One can always rewind a transformer. This might be quite tedious, but it is a low-tech thing, and is doable with some patience.

Buy a cheap manual coil winder off Ebay, takes the tediousness right out of it.

Ian.

[TheSteve]

Not a bad idea, but there are something like 6 or 8 secondary windings, I get the feeling it would be a nightmare.