CTC-9 Winslow

[Zsuttle]

I picked up a CTC-9 with excellent emissions on the original (or RCA replacement) 21CPY22. 2/3 electrolytics cans had bad ESR, so I replaced all three, along with a good amount of resistors which were 20-30% out of tolerance. I also changed out all of the maroon caps/wax paper caps that were present in the set. I randomly pulled a few and the majority had some sort of leakage.

On power up, I'm not getting any video through the set. I can get a very faint blue raster if the screen and drive are turned all the way up as well as the brightness. Green and Red are not visible. (Though there is a bit of green because of a purity issue) There isn't any sort of static on the set. Any troubleshooting ideas? I'm not sure how much troubleshooting I can do on the bench without the picture tube connected. It's a PITA to work out of the back of the cabinet.

[old_tv_nut]

Have you tested and/or replaced tubes?

[Zsuttle]

Originally Posted by old_tv_nut

Have you tested and/or replaced tubes?

Yeah, tubes have been tested. The only substitute I had to make was for a 12AZ7, which I used a 12AT7 I had laying around. Allegedly, they should substitute well. I had ordered a replacement which turned out to be a dud itself. Hence the substitute while I wait

[old_tv_nut]

Ok, then I would suggest making some voltage readings to look for any that are way out of normal. Start with the CRT cathodes and G1s. If there is a setup switch, check that it's working OK.

[Zsuttle]

No setup switch unfortunately, 385V supply is a little low at 370.

G1 voltages are slightly high (though I believe the given voltages are normal operation, not max voltages)

Blue and Green cathodes are at 353V, red cathode is at 344V. (Schematic calls for 312V)

Screen voltages are lower as the Boost source is only 660V instead of 710

[Zsuttle]

I injected a signal into the 1st video amplifier and was able to get a color unlocked, almost synchronized image. Horizontal and vertical sync were very finicky. Somewhere in the IF amplifier section, it's not getting through.

Unfortunatly I don't have any modulators capable of the necessary bandwidth. I may have a B&K 1077B laying around somewhere, which if I recall is able to do the 44MHz IF.

[Zenith26kc20]

There is a hidden bumblebee in the IF section under the removable metal shield that gets leaky. Make sure you change it.

[Zsuttle]

After poking around in the IF section, I noticed a few things. The picture detector was testing weirdly. Even after pulling it, it was still giving me strange readings. The sound detector checks as I would expect it to. Someone had already replaced both the picture detector and sound detector, not sure when. Pretty much any germanium diode should work right? I have a couple of 1N60s laying around.

I also found a bad ceramic C318, I think unrelated to my picture problem, but the cap was reading around 7kohms or so. Pulled it, still tested the same. I haven't seen ceramics fail like that before. Better to use a 50V or a 3kV? The 3kv is close to the original size (versus the tiny 50V), but not sure if there's a problem using that high of a voltage for such a low voltage application.

Lastly, I found that I somehow replaced R314 a 12k resistor with a 1.2k resistor. I somehow had them in the wrong drawer and didn't catch it when putting it in.

Fingers crossed when I fire it up tomorrow

[Alex KL-1]

Originally Posted by Zsuttle

After poking around in the IF section, I noticed a few things. The picture detector was testing weirdly. Even after pulling it, it was still giving me strange readings. The sound detector checks as I would expect it to. Someone had already replaced both the picture detector and sound detector, not sure when. Pretty much any germanium diode should work right? I have a couple of 1N60s laying around.

I also found a bad ceramic C318, I think unrelated to my picture problem, but the cap was reading around 7kohms or so. Pulled it, still tested the same. I haven't seen ceramics fail like that before. Better to use a 50V or a 3kV? The 3kv is close to the original size (versus the tiny 50V), but not sure if there's a problem using that high of a voltage for such a low voltage application.

Lastly, I found that I somehow replaced R314 a 12k resistor with a 1.2k resistor. I somehow had them in the wrong drawer and didn't catch it when putting it in.

Fingers crossed when I fire it up tomorrow

About the diode, any regular signal Ge diode can work here (almost any)...
The cap, if is a decoupling, I don't see too much trouble in using higher voltage value. Only ones for tuning or coupling can be much more critical.

[Zsuttle]

I installed the new components, still no dice. I'm not sure where to look or what I should be looking for. There's definitely an IF issue, there may be a tuner issue as well. I can't find any indication that the tuner is actually working. I was hoping that loosely coupling the oscillator in the tuner to my spectrum analyzer might indicate if it was running, but nothing. Any advice is appreciated

[Zsuttle]

I was able to determine that the AGC was taking out the tuner and the IF stages. Still no clue as to why, I used a fixed voltage supply for troubleshooting the AGC and when I was finished, the AGC started working normally. Weird...

Either way, I now have a decent black and white colorbar, but cannot get the color to lock. I ended up changing the 3.58 ECO transformer as it was seized and I was unable to perform the Color AFC Alignment. After performing that alignment, still nothing. I can get the color sync to a dead stop on the screen, but no lock.

The oscillator is running and gives a clean sine wave. The two things I did notice:

1: The input to the burst amplifier is not as clean as pictured on the SAMS. My input looks more like the plate of the color killer (though still ~50v) A lot of noise near the floor, though still the same shape overall.

2: The burst pattern is only 10v p-p versus the 30v that the SAMS calls for. I tried swapping the burst amplifier and chroma phase detector for known working tubes with no change. The burst amplifier voltages are all within the spec.

Thoughts?

[old_tv_nut]

Does the color oscillator alignment have you ground the phase detector output to adjust zero beat? If so, what happens when you remove the ground? Is the oscillator unaffected, or does the frequency change?

Try putting a voltmeter on the control tube input and see what happens to the control voltage as you ground/unground the detector. See what happens to the detector output/control tube input when the detector is not grounded and you adjust the oscillator frequency very slightly off zero beat. Trace back to the phase detector and back further to see where you are losing either burst or oscillator input to the detector.

[Alex KL-1]

Originally Posted by Zsuttle

I was able to determine that the AGC was taking out the tuner and the IF stages. Still no clue as to why, I used a fixed voltage supply for troubleshooting the AGC and when I was finished, the AGC started working normally. Weird...
...........

Well, sounds like a parasitic oscillation making rectification in some IF stage (so it throw a large negative voltage, to almost cutoff). But can be another things... difficult to predict, imagine or point out.

[Zsuttle]

Originally Posted by old_tv_nut

Does the color oscillator alignment have you ground the phase detector output to adjust zero beat? If so, what happens when you remove the ground? Is the oscillator unaffected, or does the frequency change?

Try putting a voltmeter on the control tube input and see what happens to the control voltage as you ground/unground the detector. See what happens to the detector output/control tube input when the detector is not grounded and you adjust the oscillator frequency very slightly off zero beat. Trace back to the phase detector and back further to see where you are losing either burst or oscillator input to the detector.

Well, the reactance coil got stuck. What I thought was the end was just a snag. Reactance adjustment has a lot more travel than I thought. The control voltage was not where it needed to be which tipped me off. I was able to get it locked in, and overall get a colorbar. It made a huge difference in the oscillator amplitude, which in turn corrected the burst amplitude.

Colors are wrong, and some of the colors look pastel, but overall there. It feels like there isn't enough chroma? I can't get some of the colors to where they need to be without messing up the other colors. Eg, to get white, the rest of the colors are wrong. The colors are easily washed out by the brightness

colorbar.jpg

Originally Posted by Alex KL-1

Well, sounds like a parasitic oscillation making rectification in some IF stage (so it throw a large negative voltage, to almost cutoff). But can be another things... difficult to predict, imagine or point out.

Yeah, hoping it doesn't come back. It hasn't so far. Time will tell

[old_tv_nut]

Can't see your colorbar pic. Could you post somewhere else?