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  #31  
Old 07-09-2011, 09:01 PM
ctc17 ctc17 is offline
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Replace that feedback cap in the back of the circuit that has caused us this problem before. I dont care if it tests good, replace it.
The cathode bypass caps on the output triode have the same effect.
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  #32  
Old 07-09-2011, 09:34 PM
DaveWM DaveWM is offline
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I will replace all those tomorrow.
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  #33  
Old 07-10-2011, 05:20 PM
DaveWM DaveWM is offline
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replaced a couple in the vert, no joy, need to get the right cap (.035) for the final one. I did replace the .0082 1kv and the .1 that is connected from the boost to the 390v b+. Nothing.

I scoped the PS B+ the ripple was right on the nose about 1v pp riding on the 400v. there is of course some horz but it was very small and the sams showed it (I assume since it was a fat line on the sams).

For fun I scoped the output from the sync sep. looked normal (no excessive horz noise) and also looked at the vert out grid, again nothing odd. the pairing is very subtle and comes and goes. it is not always adjustable out iwth the vert hold in fact I am not real sure the vert hold is really taking it out when it does work, but maybe its just resolving as I adjust.

I checked the yoke for leakage, even went so far as to sub the yoke, again nothing. I have the .035 cap but its an odd ball fit so I plan to just order the correct one. I also was stunned to find I did not have a 47uf axial lead cap (the cathod bypass cap).
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  #34  
Old 07-10-2011, 07:33 PM
DaveWM DaveWM is offline
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went ahead an replaced the .035, and the remaining .1 in the grid of the output triode of the 6GF7. changed the lineairity (more range now) but still have the line pairing going on. only thing left is the 50uf cathode bypass.

I am going to reset up the lineairity, then do the purity and convergence.

Its close just not perfect, like my CTC-16 in the stockholm. I will try a few more 6GF7's including the one in the stockholm just to be sure its not a tube issue.

I would really like to get these two side by side and scope the vert circuits, esp for horz noise, but they are both quite large.
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  #35  
Old 07-10-2011, 09:24 PM
roundscreen roundscreen is offline
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Did you replace the vertical center control? I have seen that control cause some weird problems. In one of my ctc16 set's it shorted out and did damage to the power supply. BTW,You have a cool set.

Last edited by roundscreen; 07-10-2011 at 09:29 PM. Reason: i don't know
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  #36  
Old 07-10-2011, 09:36 PM
DaveWM DaveWM is offline
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did not look there yet. did it test bad, or did you just change it out?

I know it works, as I used it in the setup to center the horz line doing the setup routine.
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  #37  
Old 07-10-2011, 09:49 PM
roundscreen roundscreen is offline
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[QUOTE=DaveWM;3008703]did not look there yet. did it test bad, or did you just change it out?
It had a burning smell to it so I just changed it out. Now I check the vertical center control when I pick up a new set and make sure the picture does not jump around when adjusting the control.
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  #38  
Old 07-10-2011, 10:33 PM
DaveWM DaveWM is offline
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its pretty smooth, but I will check it again. good tip.
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  #39  
Old 07-11-2011, 05:52 PM
DaveWM DaveWM is offline
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well at least I can report that I have good control of height and linearity, but still fighting the pairing. I tried a diff video source, blonder toung modulator, still there. sometimes I can dial it out some times I can't. and even if i do (vert hold) its only temp, as it pairs up again. I am going to try one more
6GF7 tube, then I think I will try subbing the tubes from my stockholm to see if that makes any diff (the sync sep and the vert osc/out).

Other than that I would have to drag the two beast together and start scoping them together, but I reall just dont have the room for that.
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  #40  
Old 07-12-2011, 07:09 PM
roundscreen roundscreen is offline
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Davewm. Try looking at the AGC and see if adjusting the AGC control calms down the pairing. Grasping at straws here but the agc can effect the sync pulse going the vertical and horizontal circuits. What does your set do when you have the color pattern generator used as a signal source?
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  #41  
Old 07-12-2011, 09:10 PM
DaveWM DaveWM is offline
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I did fool with the AGC seems to be working (goes from washed out to over contrast, but never breaks sync, but then again the box may not be putting out a strong enough signal to make that happen).

Good new!! after yet another tube swap on the 6GF7, I get a good clean sweep. I can adj the vert hold for an easy to obtain non paired up screen.

It pays to have a LOT of NOS tubes. While I have a good Mu tube tester I dont know how sensitive the grid emisson test is (its a mercury 1000).

I am calling this one fixed, at least that part.

One last little issue, seems like I often have to change the channel back and forth when the set is 1st turned on or even if I just switch signal source.

The screen will black out, sound is still there a bit weaker but there. one flip back and forth and all is good.
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  #42  
Old 07-13-2011, 12:34 AM
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Electronic M Electronic M is offline
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Sounds like it is time to clean the contacts of your tuner.

Tom C.
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  #43  
Old 07-14-2011, 10:26 PM
DaveWM DaveWM is offline
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looks like the blanked out picture had to do with the 3rd IF tube, subbed it out and all is well again. I will check it for gas or grid emissions.

I dont know why flipping the tuner would allow it to work with the old tube, but it was very consistant. I will have to cycle it a few more times before I am satisfied the problem is fixed.

I am still no completly satisfied with the line pairing, I thought the new vert tube fixed it, its better but still a bit shaky (have to diddle with the vert hold to work out the pairing).

Guess it would be a good idea to reflow the solder stakes.

I did try a convergence plug (takes the conv board out but keeps the vert working) no joy same pairing so that clears the conv board.
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  #44  
Old 07-15-2011, 04:38 AM
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earlyfilm earlyfilm is offline
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Quote:
Originally Posted by DaveWM View Post

One last little issue, seems like I often have to change the channel back and forth when the set is 1st turned on or even if I just switch signal source.

The screen will black out, sound is still there a bit weaker but there. one flip back and forth and all is good.
Try this theory on for size:

Horiz drops sync and the keying pulse hits the signal in the wrong place and this confuses the AGC.

The noise from channel flip wakes up the AGC.

This could be and probably is related to the problem with line pairing and signal level shifts.

Recheck resistor values, especially the high value ones in the AGC and any caps for leakage, where a signal from a higher voltage source is fed into the AGC (or to sync circuits.)

(Warning: With that said, I am not familiar with this model set and have not seen a schematic.)

James
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  #45  
Old 07-15-2011, 07:47 AM
DaveWM DaveWM is offline
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James,

for fun I am going to put a bias box on AGC, try clamping it and see if that does anything.

I will check the values as you described. I "think" the fix of the 3rd IF tube is working now, but I have to try it a few more times to be sure.

The agc was acting 'funny' as I was not able to distort the pic or break sync when set to max CW, the new 3rd IF seems to have fixed that.

Oh an I did not do one of the things I promised myself a while ago, always scope the AGC voltage. Look for horz hash or any thing other than a nice DC voltage.

Meters dont catch this so a scope is a must. So will be scoping the AGC voltage as well.
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