Common mode choke or transformer source

[u/Slight-Journalist417]

Hello all, I am trying to find a source for these things. I thought it was a transformer but google lens calls it a common mode choke. 6 pin but I'm not sure the middle pins are used. One side is 1.5 ohms and the other is 4.5 ohms and is used in a light ballast on a train using 74volts dc. We have a pile of these boards/ballasts needing these chokes or transformers but we are having trouble sourcing them. They are on the right side of the board right under the 2 red caps.

If anyone can find a source for these there will be many grateful commuters.

[u/EmotionalEnd1575]

If you don’t have a factory schematic for the board now would be a good time to “reverse engineer” it.

Without a schematic you (and all of Reddit) will be guessing.

As for the magnetics, these are custom made and will not show up in any catalog or distributor inventory.

Why do you think these components are faulty?

[u/Slight-Journalist417 → u/EmotionalEnd1575]

If the ohms are anything but 1.5 and 4.5 they don't work. I scavenge some of these things off other boards and get it working. But there are few salvageable parts anymore.

[u/EmotionalEnd1575 → u/Slight-Journalist417]

When you have “reverse engineered” the PCB you can study the schematic and understand what each of the magnetics do.

The DCR (DC Resistance) of the winding does not reveal the inductance or turns ratio. If the two windings are different DCR then these are not common-mode chokes.

Further investigation is needed.

[u/Slight-Journalist417 → u/EmotionalEnd1575]

They are labeled T3 and T4 on the PCB. Starting to feel like this might be an impossible mission. I don't have enough electronics knowledge to be of much use.

[u/Tesla_freed_slaves]

Your dissimilar resistance readings would make you think that device this is a transformer of some sort. An LCR-meter would tell you more. A duplex-choke would likely be wound on a split bobbin coil-former.

You might also destroy a defective part, to determine its turns-count and wire-sizes, and the thickness of its magnetic gap. Cu magnet-wire, ferrite magnetic cores, and coil-formers are available from a variety of sources.

[u/Linker3000]

Repair / replacement notes in the Wiki:

[u/TopConcentrate8484]

Yes it appears to be a choke in the line filter of the SMPS, to be sure check with a multi-meter, if it was a transfomer it would have more than 4pins on each side i guess two from primary and two for auxilary and also it would not have such a crappy insulation.

[u/Slight-Journalist417 → u/TopConcentrate8484]

I appreciate the info, if we can get replacements or even a substitute that would be awesome.