Before even thinking of messing with alignment, try subbing the last IF tube. It can cause ringing that can be mistaken for misalignment.

On that stripped gear, your shrink tubing collar is a good idea in addition to epoxy. "Belt and suspenders" redundancy.:nerd:

I tried changing each and all of the three IF tubes with some change to the ringing. Three new tubes in place of the originals does have a bit less ringing. I will try an alignment this weekend.

I'm gonna add the epoxy to the gear too.

Dave

maybe some delay line ringing?

I found that all of the Zenith color roundie convergence coils are interchangeable. The latter ones might not aesthetically correct but at least they are better made and more rugged.

The epoxy trick would not fix the broken fine tuning gear on my Zenith. The reason was that the plastic appeared to have shrunk and epoxying it would have left a considerable gap between teeth at the break. What I did was to cut an O from the end of a BIC pen, the inner diameter of which was roughly equal or slightly smaller than the gear when compressed to close the gap. With the fine tuning shaft removed, I heated it with a large soldering iron until it would just begin to melt the gear and then with gear compressed around the shaft, I slipped on the BIC ring to hold the gear compressed.

Fix ensured the gear melted into the splines and there would be no gap between the teeth where the break was. It was bit fiddley to fabricate and install, but the result worked like a charm.

I just tried adjusting the delay line termination potentiometer. It did not affect this ringing.

Post #44 shows pictures of test pattern video driven into the first IF showing ringing and then composite video driven into just after the video detector that does not show nearly as much ringing. Sure seems like it's in the IF stages.

Dave

oh my yes, I missed that. I wonder if all the little ferrite beads are in place etc. on the filament leads? My later zenith (24MC32) has several IIRC on the IF filaments. Mine also has a 22k resistor across the secondary of the IF before the 3rd IF tube. Wonder if maybe that has drifted high? I assume its there to damp out oscillation.

My first two IF stages filaments have a ferrite bead, as well as a couple more beads in the filaments some color circuit tubes. I did check and replace out of tolerance resistors in the IF stages, being careful to match lead dress as close to original as possible.

Before I started to do an IF alignment, I took some pictures of some video test pattern waveforms taken at the input to the first video amp. All the tuner and IF tubes have been tested and swapped with not much difference in the ringing. I used my Sencore VA62 to generate a channel 3 RF signal displaying the single vertical and horizontal line cross. The first video amp input scope picture shows the ringing. I then set the VA62 to generate its 10 section multi-burst which is a set of white and black vertical lines of increasing frequency from 0 to 4.5 MHz. The second picture shows the poor frequency response.

Here is a picture of the SAMs IF frequency response. Figure 1 is the third IF and figure 2 is the first and second response. The next picture shows the third IF response is pretty close to what SAMs shows (you have flip the plot horizontally to match my scope). The next picture is what I got for the first and second IF response. Its way off. The response at the 45.75 MHz marker shown should be much lower amplitude. Following SAMs alignment I tried to adjust A6, the 41.25 MHz trap and found it very hard to turn because its core was coming apart. I pulled the chassis, removed the coil, and removed the core. One end had two small pieces broken off. I tried a shorter ferrite core to see if the coil form was too tight. It was very tight. I ended up finding that a 1/4"-28 tap matches this ferrite core. So I tapped the coil form as shown in the next picture. The last picture shows the shavings removed from the coil form. The small ferrite core now threads nicely though the core. I am trying to glue the two small ferrite pieces back onto the broken core. If they hold, I will invert the core so that the broken pieces will be at the end that is not usually used for adjusting. Anyone know of a place to buy 1/4" threaded ferrite cores?

Dave

I've got a bunch (~ half of a cigar box full) of ferrite cores - how long?

I always pulled the cores from sets I junked - and at my dad's shop, I was the TV stripper/parts puller/gofer. I probably have junked over 300 sets in 30+ years. First we saved everything, then just certain chassis, then just modules, and finally, only good chassis/CRTs. My user name comes from my attitude - if you find it, keep it. Someone, somewhere will likely need it.

Cheers,

Nice. All I could find online were ferrite interference filter beads. I need two 1/4" by 5/8" long cores. If you have them, let me know the cost and shipping charges. Thanks.

Dave

I am just curious as to how this aspect panned out for you. I am working on a similar vintage Zenith and your findings are almost identical to what I was finding in my set except I can't get 190mA. More like 200 or maybe 210 at 110V. My flyback seems hotter than I would like it to be after about 30 minutes of operation. I am waiting on a replacement socket for my HV rectifier which was burned up and the 1W resistor was open (blasted in two).

I had long been searching for the source of a very light HV hissing that was intermittent. It couldn't be seen down inside the insulating cup of course. I think that we should be able to achieve correct cathode current at full line potential. Like you, I used a variable source to control this, but I don't think it would be necessary to use that or alter the line voltage in a healthy set. Also, I found that just having the raster fill the screen is not guite all my set needs. The higher line voltages (above 110V) around 115V or up give a much crisper or clearly defined picture once video comes into play.

PM sent.

I have been attempting to align my IF so my set has been on for up to a couple hours at a time. I still have my Simpson 260 in series with the HO cathode and have been keeping an eye on it. So far it is holding at about 190-195 mA. I turned it off after it had been on for over an hour and felt the flyback. It was certainly warm but not burn you fingers hot. I will use an IR thermometer on it next time I have it on for a while and report the result. If it would help, I can also take some voltage readings. You may want to replace all of the capacitors in the HO section and verify that all of the resistors are within their tolerance. A leaky HO grid cap could elevate your current.

Dave

Thanks very much for your kind help!

Dave