Filter choke winding in smps in Kef sub

[diydidi]

Hi All. I have this sub for repair. Turns out the secondary filter choke L5, was shorted. I unwounded the two windings from it, and put new enameled wire on it. Now the smps works, but, on the one rail I have the 55V as stated on the schematic, but on the -55V rail I get -75V.
There is a slight inductance difference between the two windings.
My question is how do I wind this properly? I'm not sure about the start winding points as indicated on the schematic. Do I wind the two wires in parallel on the core or what?
It is my belief that I wound the coil incorrectly.
Any help will be appreciated.
See attached schematic.

[R.G.]

Does L5 have two windings, one in the + side and one in the - side?

You may consider the little black dot on the schematic to be the start of the winding in all cases.

It is usually best to wind them "bifilar", which is as you suggested, winding both in parallel at the same time. Label the "start" end of both wires, wind them in parallel, then connect the wires to the proper terminals on the inductor so the start and finish ends of both windings will go into the correct holes on the PCB.

[diydidi]

RG. Thats correct. Two windings on one core.

[Steve Conner]

What RG said. The design calls for two identical windings with tight coupling. Wind it bifilar, that is winding two pieces of wire at once. Label the two "starts", and connect them where the dots are on the schematic.

If the two windings have different turn counts, you'll have unbalanced rail voltages. If one is hooked up backwards, you'll have very unbalanced rail voltages and possibly a large release of magic smoke.

[diydidi]

Great. I think I understand. One more thing. Do the start points as in the schematic look right to you guys? Shouldn't they both be on the transformer's side?

[Steve Conner]

The start points are correct. This isn't a common-mode choke like you normally find in mains filters, it's a coupled inductor to balance the rail voltages. To do its job, the DC currents in the two windings have to add and magnetise the core, not cancel out.

[diydidi]

Thanx guys. Will give it a rewind.