[EDITED] Reverse engineering a transformer without knowing all secondary turns

[gkmaia]

Edit: subject and basic information

This may be a long shot.

I have a high voltage switching ferrite transformer that has failed. Due to the construction of the transformer I could not retrieve all its windings. The only winding I could retrieve was the primary.

The oscillation is caused by the feedback winding forward biasing a transistor at the end of the primary winding.

Is it possible to recalculate the secondary windings taking in consideration:
- cylindrical core area 80mm2
- operates at 50Khz
- ferrite Bsat ~0.3T
- primary (pin 4-5) has 30 turns. Is feed with rectified/decoupled +120VDC oscillates at 240v pk-pk.
- feedback (pin 3-6) is feed with rectified/decoupled +2.3VDC oscillates at 4.5v pk-pk
- secondary A - (pin 9-10) oscillates at 2v pk-pk
- secondary B pin 1 ground
- secondary B pin 2 -120VDC from rectified/decoupled input
- secondary B pin 7 -220VDC from rectified/decoupled input
- secondary B pin 8 -2.7KV RMS supply to CRT

Regarding the current I can still retrieve the winding gauges.

[Chris56000]

Hi!

Try heating the transformer with a heat-gun - this might soften the resin enough to enable you to chip it away so you can get at the remainder of the windings!

Failing that, you might find one of the other Tektronix oscilloscopes that uses a similar type of e.h.t. oscillator has a transformer you can use in your T910 with a little circuit adaption!

Chris Williams

[gkmaia]

Heating did not work... unfortunately.

But I guess that could be a cool project. Trying to figure out what the other windings are based on the primary and the schematics.

Not sure if that is possible. But would be a cool project if it is.

[andy3055]

Unless you took the transformer out of the board or lifted other parts to isolate it, you could be reading through other components and the readings will throw you off.

I am, at the moment, repairing my 465M and found the issue was the tripler. I had to isolate it before I was able to stop the fuse from blowing. I was glad to find that the transformer is OK.

Try these guys: https://www.sphere.bc.ca/test/tek-transformers.html#catalog

Even if they have not listed it, they may be still having one in their pile of stuff in the back! The site also shows a couple of them that has clips holding the 2 halves of the ferrite core together. If you break the ferrite core you are dead! If you drop it, it is gone. I am saying this not to insult your knowledge but because it is very brittle, delicate and fragile. So, be very gentle with it.

Good luck