John,

Here are some pictures to show exactly what you're referring to. The first is a NOS FLY-107 flyback with no circuit connections. The second is the same flyback, but with the filament winding for the HV rectifier shorted directly. The third is with an actual 1B3 filament across the filament winding.

These all show the expected behavior. A dead shorted turn has a huge effect, and a turn shorted with a small, but finite resistance, has a noticeable, but smaller effect.

The CT-100 flyback cases I've shown always had both the HV rectifier (3A3) and the focus rectifier (1X2) unplugged, since I was aware that this could be an issue. In the case of the post above with 6 pictures, the CT-100 flyback was tested with no connections whatsoever (no yoke, no filaments, no pulse windings connected to anything).

The one case I want to go back and double check is the Emerson 637 picture above, where I mention the yoke is disconnected and other connections didn't matter. I definitely tested it with the 1B3 removed, and also tested with most other connections removed (including yoke), but I want to make doubly sure I did it with all of the above disconnected simultaneously.

The Crosley 9-407 case above had everything connected, including HV rectifier tube filament.

So far, all tests are consistent with the CT-100 flyback having a shorted turn. The only confusing cases that are causing me to hesitate are the ringdowns on the Emerson 637 set, where I did not see the expected result for a working flyback.

The CT-100 ringdown isn't as fast as the direct shorted case posted here, but I think that makes sense. Shorting the filament winding has very low resistance, since the filament winding is thick wire. An unwanted short inside the HV winding (such as what I think I have on the CT-100 flyback) will have higher resistance both due to much thinner wire, and possibly because the short itself has some resistance (dirty/burned contact point).

This has turned into quite a sidetrack, but I'm actually glad to develop a good technique for testing flybacks, with enough experience on many different flybacks to have decent confidence in the results. These ringdown scope traces are probably a more thorough method of testing than simply relying on what some particular piece of equipment says in a "good / bad" test.

I think you are right, the resistance of the HV coil wire ends up being in series with the shorted turn and thus reducing the effect of the shorted turn on the ringing response.

One other thing you can try.. remove the solder from the terminal which connects to the plate cap of the HO and remove the flyback wire which goes to the HV winding and leaving the flyback wire going to the primary attached to the terminal. Run the ring test again, and you should see a normal response, proving the shorted turn. Of course, doing this does have some risk, one could break either of the two wires in such a way that they could not be repaired. But as the flyback is most likely NG, you don't have too much to loose.

Hi John,

I can do that this evening when I get home from work, but I don't understand why disconnecting this wire will change anything. If there is a shorted turn in the HV winding, it will still have the same effect, whether the bottom end of the HV winding happens to be connected to the primary or not. Top end, of course, is open circuit with the 3A3 removed. A completely isolated shorted turn will still overdamp the ringdown, just like a shorted filament winding, wouldn't you agree?

Um.. not sure i follow correctly. But you're saying leave the HV winding ('tire') electrically floating but still physically in place(?).
Would not a shorted turn in the 'tire' still load the primary whether or not it's electrically connected? Seems like you'd have to physically remove the tire to do the test.
Or maybe i'm misreading whut U sed. :o

Yeah, my bad... what was I thinking? Bit I am pretty much convinced you have a shorted turn.

I retested the Emerson 637 set, which appeared to show too few cycles for a known-good flyback when I tested yesterday (and posted on page 2). This time I really had all connections removed, and it looks decent.

I think previously I had noticed that removing the 1B3 in that set had only a minor impact on the ringdown and then plugged it back in. However, after removing all other connections, it may have been having a bigger effect, being the only remaining load. So the previous picture with "no yoke" still had the 1B3 filament load. Got to be careful to make sure all connections are removed for a final test of a flyback.

So I think that removes all doubt about this particular method for testing flybacks. If you get something like 10 decent cycles of ringing or more, the flyback is OK. If you don't, it has high loss (low Q) from a shorted turn.

Looks like this will be a good technique for checking flybacks going forward.

Decided to unwind the HV winding of the flyback and see how many turns would need to be removed to find and remove the short. I was hoping it would be a short in the outer layer or two of the coil.

Got started by removing the black hard shell that coats the outer diameter of the HV coil. The material is quite different than most flybacks -- quite hard and durable. It was difficult to nibble at it with a diagonal wire cutter. First picture below shows the first nibbles out of the shell. Second picture shows the whole thing removed, which I also used a Dremel tool to assist. Once I get a few big nibbles out, then I was able to crack the whole thing off easily.

I left the Ringer and scope attached the entire time while I unwound the coil, so I could see immediately when the short was gone. After unwinding a few tens of layers, I could tell the unwinding was getting more difficult, and one spot in particular looked well cooked. Getting closer to the short!

Eventually got the short, and I also unwound one more layer of well cooked wire with the thought that a damaged winding layer would be likely to fail later. Still there are quite a few cooked layers present, but the short is gone. Alas, I had to remove quite a bit of the coil (perhaps something like 15%). Will it have enough HV back in the set? We'll find out.

The new ringdown is shown in the 3rd attached picture, and looks convincingly good. The last picture is the remaining HV coil, obviously smaller than when we started. I'll reattach the 3A3 anode lead and reinstall it in the set.

Dang, this is one of the more fascinating of troubleshooting mini sagas.

:)

Good Work! It will be interesting to see how much HV the coil can produce now.

jr

If it is not good enough you could always take the removed wire dip it in lacquer a few times to build up it's insulation and try to rewind that wire back on to the fly...

Looks like it will produce 20 kV. :thmbsp: The HV regulator is working, too. I can reduce the HV down to about 18.5 kV and up to 20 kV. When everything is working, I imagine I'll have to run it around 19 - 19.5 kV, just to have some headroom to maintain proper regulation.

I had also been thinking that if necessary I could try to add some turns back on the flyback. I won't be using the wire I removed, however, as you can see in the first attached photo. I didn't disassemble the flyback, but left everything enclosed in the core and frame while I unwound the coil. This meant that every few turns I had to cut the wire, to avoid having to pull a lot of wire through the opening. The insulation generally was destroyed as I unwound the coil anyway, so no use thinking about salvaging the old wire. Some new wire could be added with some kind of plastic mandrel walls to make winding reasonably straightforward. However, it looks like I may not need to do that.

The last picture shows a closeup of the flyback in the set. I coated the outside of the coil with some red insulating varnish. I may beef that up with something more at some point. I didn't want to glop too much on there yet in case I needed to add more windings.

As you can see, the focus rectifier is still not connected. Now I need to deal with the vertical dynamic convergence transformer issue and other things.

FYI: With the focus rectifier operating normally and with a low-contrast image, my CTC2 will crank out 22 kV; I set the HV 2 kV below that, and overall operation is satisfactory.

Pete

Tom that's a pretty good job, I would have done that too.... I think that if you keep the hv too high, it will draw extra current on the primary... What do you guys think....

Congratulations on a really delicate difficult operation on the flyback. Sounds like another historic CT100 is well on its way to being saved. Hope it all works out well.

Tom-

I am very happy to see your progress on the flyback problem, and I look forward to further news as you continue the project. Nice work!