CTC-9 tint control oddness

[DaveWM]

Originally Posted by old_coot88

That looks like it might also have a demod problem. Have you DeOx'ed/reseated the demod tube in its socket and/or subbed the tube?

I presume you mean the 12AZ7 dual triode (ref osc goes to K's chroma info to grids), I have not, but will. Something else that was odd that I did not notice before is I have red screen background (there are RGB bkg pots adj G1 and GB scr pot on G2 which is a little different than I have seen on later models) has to be set to the min for the grey scale to work the G and B are not at min, nvr had a CRT where the red was the strongest gun. So the G2 red runs wide open and you adj the G1 red with a pot.

I prob should check the kine pins for voltages to make sure all is well there.

what makes you think there is a demod problem? seems to me the colors are correct just lacking in phase shift of the ref osc.

[Dave A]

I have a Philco Portacolor clone with the exact same problem. Someday....

[old_coot88]

Originally Posted by DaveWM

I presume you mean the 12AZ7 dual triode...

...what makes you think there is a demod problem?

Well, it seems like blue portions of the chroma information are suppressed or 'not there', hence not able to render purple in the flesh tones.

Meanwhile, luma information appears overly blue due to blue screen being set a tad high.

Have you set the grey scale (i.e., with color turned off, each gun extinguishes at exactly the same screen setting)?

Re. The Portacolor clone (if it's a GE clone), doesn't it use that uber-simple 'ringing burst' in lieu of a referance oscillator?

[DaveWM]

the grey scale seems fine, when I turn down the color I get a normal looking BW pic as I adjust the brightness up and down.

the video is not the best, seems to be messing up the blue (there are times when the screen looks predom blue and its not.

I will get a NTSC color bar signal on it to make sure its working properly.

[DaveWM]

https://www.youtube.com/watch?v=Yr_T0-Em0qQ

color bars showing lack of tint shift.

the plan next will be

exchange color output tubes just so see if there is any change, sub a new demod tube (uses a single dual triode for the X and Z) again just to see if any changes.

if no improvement, I will pull the chassis out some so I can get to the test points. The sams has me grounding the output from the chrroma band pass trans (not sure why, this is point N on the sams) then puttting a vtvm on one of the pins of the 6AL5 phase detecting diode and adjusting the 3.58mhz osc coil for max deflection, then adj the burst trans again for max deflection, lastly grounding point O (the ref voltage from the two matched resistors) and setting the reactance coil for color bars that are still or nearly still. (of course this is with the tint control set to the middle of the range) I have not done the max deflection setup part before so I will measure the coil settings before adj JIC I need to get back to where I am now.

[old_coot88]

Yep it looks like it do got a tint phase issue. That 'blue in the luma' effect is what had me hopping down the bunny trail.

[DaveWM]

tube swap did nothing, adj the burst amp transformer fixed it. I did it without the VTVM just tweeked about 1/4 turn and the tint range started working fine. Did not feel like pulling the chassis to start grounding out test points, I think I could have gotten away with a tube socket extender and forget grounding the N test point, not sure why they wanted the chroma signal grounded since the point was to peak the burst, but anyway it worked.

[old_coot88]

Great!Wisht there was a 'clapping hands' smiley.

[DaveWM]

thanks OC, will post up some new video later with the color bars, tried just getting some off the air stuff, but they keep changing the image so quickly that its hard to get a good shot to show the shift. I swear I think TV is speeding up shows, must be something to do with cramming in more commercials and then constant scene change to try and hold viewer attention spans. I have a DVD of the wizard of oz that I typically use, and freeze frame to get good color for setting flesh tones up.

[DaveWM]

https://www.youtube.com/watch?v=SoJ8fNDGwgE

latest video showing tint functioning as it should.