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  #16  
Old 11-13-2013, 08:19 PM
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Comparing winding resistance will likely not reveal a shorted turn, as the short will only remove a small number of turns resistance from a large resistance total.
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  #17  
Old 11-13-2013, 10:18 PM
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Do you have access to a "ringer" tester? They are pretty good at spotting shorted turns...
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  #18  
Old 11-13-2013, 10:48 PM
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Have you checked the value of the cathode resistor on the 6CD6 yet, or read for cathode current? All this talk about serious mods so soon, and we're not even certain the flyback is the problem yet! Slow down, take a deep breath, do some trouble shooting. In the end if it ends up being the flyback, at least you did your homework first. All I'm saying is I definitely rule out every other possibility before jumping straight to unobtanium parts like flybacks, especially in a chassis like the CTC-2 where they rarely fail.

There are several controls on the chassis which impact HV production:

Drive varies the waveform going into the grid of the output tube, if it's low in amplitude the negative bias of the tube will not be right and tend to cause more current to be drawn heating things up. R175 (Sams) on my set had drifted causing incorrect operation of the drive control, I couldn't get rid of the drive line till I got the correct resistor in there.

Horizontal may be off frequency (wave coil), which will cause bad sync and low HV production- 2 of your original symptoms. The waveform in the oscillator itself may not be the right shape (equal peaks), the cure for both of these is to do the horizontal setup procedure in Sams.

HV pot may have drifted, if so the shunt may be dragging down HV even if everything else is working correctly.

You have a known bad convergence transformer- stop thinking about the fly till you cure that problem.

Is the CRT boot clean? If not, it will make a sizzling sound and even if it's not it could still have a path to ground somewhere that's draining the high potential away from the CRT. I went through 3 different ones before I found one my set 'liked'.

Or any one of a million other things on a very long list, but the point is you have to start somewhere before assuming the worst. My starting point is always to make sure the horizontal oscillator is in perfect health and on the right frequency FIRST. All other circuits in the chassis depend on horizontal to tell them when to do their thing: burst keying, color killer, convergence, ect. All other circuits are secondary to horizontal being correct.

My AGC pot was also bad, leading to a lengthy and unnecessary foray into CTC-2 IF alignment. Much was learned, including the important lesson of LOOKING FOR SIMPLE FIXES FIRST!

Slow down, maybe even walk away for a few days and think about it. Put John's convergence transformer in it, then retest. If it's still jacked up, go through the horizontal circuit with a fine toothed comb. Report to us with your results, the last thing we want is for your fly to be bad.
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  #19  
Old 11-14-2013, 01:30 AM
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N2IXK,

I have a Ringer, but it works poorly. I've been on the lookout to buy a better one, but that's one acquisition I still need to make. The one I have has a sticky meter movement, and I have not been able to improve it. That ends up making the readings very unreliable. Would be nice to have a good Ringer right now, just to make doubly sure that the problem isn't somewhere else and the flyback really shows the expected lossy behavior in a Ringer.

Miniman,

I'm actually reasonably experienced at TV restoration, so quite a few of the important things you point out are indeed things I already paid attention to, or have reasons to believe are not relevant for the particular way I'm going after the problem. Nonetheless, I'm glad to see you ask all the right questions here, since I don't want to leave out something critical and make an unnecessary mistake.

The horizontal frequency is correct, because I can see just enough video stuff on the screen to tell that it actually locks weakly to a TV signal on the antenna input. Nonetheless, I got out the frequency counter to make sure, and yes, it's ~15.75 kHz. My ear had also confirmed from the start that the pitch was "about right."

HO grid bias is -46 volts, and the peak-to-peak drive waveform is 150 V on the grid (cf. 120 V P-P in Sams), adjustable with the drive control.

HO cathode current is 193 mA (cf. 167 mA in Sams), which seems reasonable given the improper power dissipation in the flyback itself, although if any of these numbers raise a red flag for any of you, don't hesitate to speak up.

The real smoking gun on suspecting the problem is a shorted turn in the HV winding of the flyback transformer is that it is getting quite hot in about 1 minute of operation, with neither the high voltage rectifier (3A3) or focus rectifier (1X2) connected. The only way there can be a load on the high voltage winding is if the load is within the coil itself - a shorted turn or something else very lossy. The heat really does seem to be generated in the HV secondary winding; it is much hotter to the touch than the primary windings. My finger may not be a 100% reliable temperature sensor, however, so I've checked it many times and I seem to be coming to a consistent conclusion on that.

I have the convergence transformer out of circuit for all of these measurements (by disconnecting the focus rectifier), so even though it looks quite likely that it is bad, it can wait until the HV problem is cured. It is definitely not having any effect on the flyback right now.

I have the CRT out of circuit most of the time, but have connected it a few times (as well as the 3A3 HV rectifier) and can see a very dim, out-of-focus raster on the screen, and it does not substantially load down the already weak HV (because the CRT anode current is almost zero under these circumstances). HV is quite low, around 10-13 kV -- a little lower in that range yesterday, a little higher today. No evidence of any current in the 6BD4 regulator tube (which is how it should be with the HV too low). Disconnecting or connecting the regulator tube has no effect (which indicates it is working correctly, or at least doing no harm).

I think I'm properly covering all the things that could account for improper flyback function, but if you see something I missed, I'll be more than happy to go after it. I, too, am not eager to prematurely modify the flyback in an irreversible manner.

One could always suspect the yoke, but if it's bad, it shouldn't be causing my HV secondary on the flyback to get hot. I have a test yoke I can connect, and perhaps I'll do that next just to make sure (in case my finger temp measurements are misleading me as to what's the source of the heat in the flyback).

On the other hand, there are lots of other circuits in the set that have nothing to do with the horizontal sweep, and my preference is to solve this problem before going after all those. I'm confident we'll get this set fixed in a step-by-step manner, and for me, horizontal sweep and HV are priority #1 pretty much in any set I work on. So indeed I agree with you that the horizontal oscillator needs to be functioning properly as step #1, and that was indeed done here.

When I get to the color circuitry, that's where I've got the most learning to do. I've restored dozens and dozens of black and white sets, so I've got a decent grasp of all of the circuitry and functions in black and white sets. But color is something new, so that part of this experience is going to be educational!

Last edited by Tom Albrecht; 11-14-2013 at 01:41 AM.
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  #20  
Old 11-14-2013, 09:49 AM
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The B&K 1076 analyst is a good flyback checker. Another good way is with a WO-91B RCA scope with the mod from RCA bulletin. The mod is adding a capacitor to get a sweep output. The pattern during test is a good ringing waveform if the flyback is good.
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  #21  
Old 11-14-2013, 01:05 PM
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I spent some time last night and this morning trying to check the flyback and yoke in additional ways.

I have a Sencore SS137 Sweep Circuit Analyzer (picture attached) that I had not used before. I spent a little time making repairs to it (new electrolytics, fixed a broken wire) and confirmed that everything on it appears to be working properly. It has many functions, of which two are useful here. One is that it has a substitute horizontal yoke coil. Connecting this substitute yoke in place of the yoke in the set is supposed to tell you whether there is a problem with the set's yoke. Connecting the sub yoke, I find the HV is slightly higher (14-15 kV), but no where near where it should be, so my conclusion is that the yoke in the set is probably OK. It also measures the current in the substitute yoke and displays whether it thinks the flyback (and overall horizontal sweep system) is OK. Although the measurement doesn't seem very sophisticated, it does claim the flyback is bad (provided the surrounding circuitry is functioning normally). The meter has lines for various deflection angles of black and white sets (above line is good, below bad), and a single line for "color" sets, requiring the highest amount of measured signal. My result was that the meter came up to the level for a 50 degree B&W tube, which is way below what is deemed correct for a "color" tube. Not sure I trust this one-size-fits-all test, given that the 15GP22 is probably a bit unique, and its sweep system may not have enough in common with what this tester thinks is appropriate for "color" to give a trustworthy result.

Fant's post above reminded me that people sometimes do a ringdown on a scope to check a flyback. Although I have never done that before, it occurred to me that although I don't trust the meter on my Ringer, it does put out pulses. I captured the ringdown on a scope (see attached photo). What do you guys think about the waveform?

The manual for the Ringer says 10 cycles is the boundary between good and bad, but I don't know how small a cycle needs to be before it is no longer counted. Perhaps one of you knows.
Attached Images
File Type: jpg Sencore SS137 Sweep Circuit Analyzer.jpg (89.9 KB, 57 views)
File Type: jpg CT-100 Flyback Ringdown.jpg (25.4 KB, 82 views)
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  #22  
Old 11-14-2013, 02:00 PM
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I have no idea where the threshold is set for the ring test, but I would judge that to be somewhat less than 10 rings.
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  #23  
Old 11-14-2013, 02:23 PM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by Fant View Post
The B&K 1076 analyst is a good flyback checker.
I used the 1076 with 100% success back in the day. Even with its simple neon indicator, it never once gave a false "bad" reading or showed a bad unit "good".
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  #24  
Old 11-14-2013, 02:29 PM
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I would try the ring test on several known good (B/W is ok) flyback transformers to get an idea what the display should look like... I agree that that seems to fall short of the 10 ring threshold, but what does another flyback do in your set-up? Perhaps the scope input impedance is lower than that in the tester circuit, causing more rapid damping?

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  #25  
Old 11-14-2013, 02:49 PM
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ChrisW6ATV ChrisW6ATV is offline
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Tom-

I am not too far away from you, and I have several devices that include flyback-testing ability if I remember right. They are a B&K 1077, a Sencore VA48, and a Sencore VA62. The catch is that I have not yet used any of them to do flyback tests, so there would be some learning to do in the process. I am happy to lend you any of these instruments and/or to help out if I can. I also have a CT-100 that I restored a couple of years ago, and I did a lot of work on its horizontal circuits as well. (In fact, it is still not 100% either, but I had put it on hold while other tasks came up.) You can probably find its discussion here with a search of my name.
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  #26  
Old 11-15-2013, 01:04 AM
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Hi Chris,

It sounds like your situation is not so much different than mine -- various equipment that should do the job, but nothing that you've used often enough to really have confidence in its accuracy. I also have two B&K 1077 units that I could repair and try.

All,

I did a bunch of ringdown tests on various flybacks to see how they compare to what I'm seeing on the CT-100 flyback.

Here are the attached pictures in order:

1. CT-100 flyback, this time isolated from the circuitry (all connections removed, including yoke) - looks like 5 or 6 decent cycles only

2. Stancor A8134 NOS flyback, no connections

3. RCA 104309 NOS flyback with big coil, for 110 deg CRT (probably black and white), no connections

4. Traid D305 NOS flyback, for color set, no connections

5. Traid D311 NOS flyback, for color set, no connections

6. Traid D313 NOS flyback, for color set, no connections

Quite an obvious difference in terms of seeing a lot of decent ringing cycles on all the NOS yokes.

So that all looks nice and conclusive, but wait until you see the next post (I can't upload any more pictures in this one).

Last edited by Tom Albrecht; 11-15-2013 at 01:48 AM.
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  #27  
Old 11-15-2013, 01:09 AM
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Tom Albrecht Tom Albrecht is offline
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Now a little more data to make things confusing...

I happen to have an Emerson 637 in the shop. It's a 10" B/W set from 1949 and it works very nicely. Took the chassis out and tried the ringdown test on this set with a "known good" flyback, and look what I get!

1. Emerson 637 ringdown, with flyback in circuit (yoke, etc., connected)

2. Emerson 637, with yoke disconnected (removing other connections had little effect, also tried pulling 1B3 to remove filament load, but didn't matter)

3. Merit HVO-5 NOS, very similar to what's in the Emerson. No connections.

OK, so the Emerson flyback doesn't look very good in a ringdown test, but it works in the set! And it compares badly with an NOS flyback that looks very similar and might even be the right replacement (it's the fairly common early style flyback used in the late 1940s with a more metallic-looking core, not ferrite or laminated).

HV in the Emerson is 9 kV, which is just what it should be.

Not sure what to make of that!
Attached Images
File Type: jpg Emerson 637 with yoke connected.jpg (37.1 KB, 10 views)
File Type: jpg Emerson 637 no yoke.jpg (38.4 KB, 9 views)
File Type: jpg Merit HVO-5 NOS no connections.jpg (41.6 KB, 10 views)

Last edited by Tom Albrecht; 11-15-2013 at 01:47 AM.
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  #28  
Old 11-15-2013, 01:52 AM
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Tom Albrecht Tom Albrecht is offline
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And a couple more for a sanity check.

1. Crosley 9-407, with all circuits connected. Similar early style flyback as Emerson 637 above (the other one which rings down with very few cycles, even though the set works well).

2. GE 805 Locomotive, with all circuits connected. More cycles on this one. This set also works fine.

Still not sure how to interpret the Crosley and Emerson results. Maybe the early style metallic looking core is lossier than more modern ferrite cores? Then why does the Merit HVO-5 NOS flyback not show the same loss? It looks very similar in construction.
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  #29  
Old 11-15-2013, 02:15 AM
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Quote:
Originally Posted by John Folsom View Post
I have no idea where the threshold is set for the ring test, but I would judge that to be somewhat less than 10 rings.
Reading some of the details in the Ringer manual, it says that the usual threshold is 25% of the amplitude of the first cycle. So the bar is pretty high.
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  #30  
Old 11-15-2013, 11:00 AM
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Tom, when testing with the flyback in circuit, if you leave the rectifier tube in the socket, the filament circuit looks like a shorted turn. Take one of your out of circuit flys and put a single shorted turn of wire around one leg of the core and compare the results.
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