#46
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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. Last edited by old_coot88; 02-03-2015 at 11:35 PM. |
#47
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I'm gonna add the epoxy to the gear too. Dave |
#48
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maybe some delay line ringing?
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#49
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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. |
#50
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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 |
Audiokarma |
#51
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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.
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#52
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#53
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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.
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#54
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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 |
#55
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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,
__________________
Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
Audiokarma |
#56
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Dave |
#57
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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.
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"Face piles of trials with smiles, for it riles them to believe that you perceive the web they weave, and keep on thinking free" |
#58
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PM sent.
__________________
Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
#59
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Dave Last edited by Zenith6S321; 02-10-2015 at 06:42 PM. |
#60
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Audiokarma |
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