Neat trick: Ringing a flyback with only a scope

[VintagePC]

I found out today you can ring test a flyback with nothing more than a scope (and maybe a handful of capacitors of different values).

All you need is a scope that has a square wave output of some kind of at least 10vpp.

My Tek 453 has a "gate" output that goes high when channels are triggered.

Wire it up to one of the horizontal primaries of your flyback. and connect your probe in parallel. (In my case this was a little complicated since I used the A gate to pulse the flyback, and the B channel to observe the ringing. It's easier if you have a 10vpp cal output or some such as you don't need to force A to trigger in addition to your monitor channel).

If you did it right you should see a pulse on your probe. Now dig through your capacitors and bridge the channel with a typical TV type film cap - 0.1 to 0.01 µF.

You should get a nice ring (see attached). If you dont, try a few values or a different terminal, it depends on the resonant frequency of your fly. If it won't ring, you've probably got a shorted winding.

Best done with a known good fly first to get a feel for it - Once you get a ring... try shorting another winding, such as the HV rectifier filament (just like a single shorted turn)... and you'll see severe damping of the oscillations.

Pretty neat, eh?