A Zenith color decided to follow me home, hoping to avoid being upcycled. It's a remote model with power tuning. I managed to massage the set into fairly decent working order, temporarily, with the exception of the tuner motor which had a broken gear, and lack of fine tuning, which for some reason won't engage. (Will need to pull the tuner to try to address this)

Sam's
https://drive.google.com/file/d/1BpqWYHS16GLsWxCcBI2-2XYCnGdmX5An/view?usp=sharing



https://i.ibb.co/hLHHBq3/IMG-6281.jpg

https://i.ibb.co/HKnpcHr/IMG-6377.png

The color was always slow to come on, and after a couple days of running, I noticed the color not able anymore to achieve sync. I decided to try to finesse the chroma bandpass (A24), and while doing so, the pic started to drop out and I was left with very dark patchy video. Retrace lines were also visible.

https://i.ibb.co/197RXtB/IMG-6414.png

I tested all of the video, agc/sync and tuner tubes. Tested the Chroma, R-Y and R-B tubes.All were ok. Video amp transistor tested fine.

Video detector and all other signal diodes tested fine. Source voltages and electrolytics test ok. Tested all resistors around all tubes concerned and all were within spec. Certainly no burnt or open resistors.

After turning the set off and on, all that we have now is a blank raster. RF, IF and composite video does not get through. I've been banging my head trying to find the cause of this weird condition. I haven't dealt with a more complicated problem and I'm hoping a veteran can help point out something obvious I may have missed.

https://i.ibb.co/gFmgGGx/IMG-6416.jpg

Injected signal from VA-48 into IF stages and there was no video, only sound. Injected composite into the Video output and only a very very slight pattern was seen.

AGC Bias

Biased point "A" on schematic, per alignment instructions, with up to +/- 25v and this had no effect on pic.

Waveforms

Injecting RF from pattern gen into the antenna terminals, no waveform was found in the IF stages.

A sync pulse from the flyback was seen on the AGC plate, but no video sync pulse was found.

Voltages

V1 (1st IF) No appreciable voltages were found on any of the pins.

V2 No voltages, except for pin 7, which has 241v on it

V3 Normal voltages

V4 (1st Chroma) No voltages found, except for an incorrect one found on pin 8 which was 199v (Should be 85)

V5 (Vid. out) Normal voltages

V6 (Sound/Sync) Normal voltages

V8 (AGC) Normal voltages

V10 (2nd Chroma) Pin 6 - 1.5v (should be 12.5), pin 7 - .26v (should be -25), pin 8 - 103v (should be 205), pin 9 - 207v (should be 240)

Controls

AGC pot was found to be in working order. Varying this control produced no change, other than slight brightness variation. Brightness and contrast controls did have an effect. Bias does vary brightness.

Here's the Sam's

https://drive.google.com/file/d/1BpqWYHS16GLsWxCcBI2-2XYCnGdmX5An/view?usp=sharing

Start with the blank white screen. Most likely IF problem. Now we
use the built in signal ( noise) injector........
Turn channels. If you see & hear crashes of the tuner switches its the tuner.
If you dont then its IF problem.
You can do the same with the IF. While running take out then put the
IF tubes back in. Watch for crashes as above. 1 IF, 2 IF, 3 IF its a chain.
The pix with retrace has color info but not video. Trace the video amps & out.
Nice sets, I had one in the maple flavored cabinet back 30 yrs ago. Great sound.

BTW go easy on any coils. Flag your tool so you can go back. Also do not trust tube checkers.

73 Zeno:smoke:
LFOD !

The 3rd picture from the top shows the set having lost the luma (video) signal, with the chroma signal still present. The two most frequent causes are:

1. Dirty service switch. Try working the service switch and giving it a shot of Deoxit or similar.

2. Heater-cathode short in the CRT. Try rapping on the neck (not too hard):eek: while watching the screen with a mirror.

Oh what a sweet Zenith chroma color, my grandmother had a very similar set for many years and gave very little trouble. I do recall the service switch was a trouble maker and I had to squeeze under the set to reach up and cycle it... was maybe 11 at the time.

My advice for the present is to not only trace out the voltages but also check the resistor values of the low level areas rather than twisting the coils. Clearly you have your work cut out but the rewards will be many. Awesome find

" Voltages

V1 (1st IF) No appreciable voltages were found on any of the pins.

V2 No voltages, except for pin 7, which has 241v on it

V3 Normal voltages

V4 (1st Chroma) No voltages found, except for an incorrect one found on pin 8 which was 199v (Should be 85)
"

You have a loss of B+ to those sections.... V1, & V2. At least V1....
245V source - Open resistor R56, R55, R52? Cap across them shorted...? Some Other Resistor??
If It's True you actually have " V1 (1st IF) No appreciable voltages were found on any of the pins."
V1 6EH7 tube, V2 6EH7 tube....

" V4 (1st Chroma) No voltages found, except for an incorrect one found on pin 8 which was 199v (Should be 85) "
Tube is not turned on, Not Conducting, no V Drop across load resistor...... To be expected high, above 125V
because tube is not conducting.....

" V2 No voltages, except for pin 7, which has 241v on it " - V2 Not turned on Not Conducting.
Path from pin 7 to 245V source ok....

.

OK, update. Discovered that 2 of my IF tubes 1, 2 were oriented wrong. This is easy to do when there are no keys in the socket. Voltages on all IFs are reasonably acceptable now. Voltages on the Video out seem ok. Whether I put RF on the antenna terminals or inject an IF or composite signal, I get the same result; sound, plus a very faint image and moving horizontal lines corresponding to video information.

Video output tube, V5 tests normal on 2 testers.

Checking CRT pin voltages, these appear to be normal and within a reasonable range.

Here's what we are currently looking like:

https://www.youtube.com/watch?v=MXUI51ZKcUE&ab_channel=Silvertone58

Now , I'm onto the V4 Cathode Follower. The voltages are not correct here.
pin1: 0v (should be2.5v), pin2: .4v (should be 3v), pin3: 220v (ok)

Composite waveform into V5, pin 2
https://i.ibb.co/58WHjcg/IMG-6441.png

Composite waveform out of V5, pin 7
https://i.ibb.co/Qp1Qdgf/IMG-6442.png

We can see hardly any signal is leaving the tube, even though there's around 310v on that pin.

Chroma BP 1, 2 voltages are wrong

V4 pin6: 0 (OK) pin7: .06 (should be -.5) pin8: 182 (should be 85) pin9: 182 (should be 85)

V10 pin6: 1.5 (should be 12.5) pin7: .26 (should be -25) pin8: 100 (should be 205) pin9: 203 (should be 240)

Bear in mind that I'm powering off a sencore powerite and since its meter is broken I'm using a Kill o watt, so all I'm looking for are voltages in the ballpark.

The issue here isn't with the CRT, your pictures confirm this. Now is there any chance a 6EJ7 hasn't been transposed or replaced with a 6EH7? I'm guilty of this and spent many hours chasing my tail looking at low video output levels. Double check this.
Tubes are ballpark devices anyway so I wouldn't worry about a few volts, its more about the actual differentials.
I'm trying to look at V4 now but the google supplied schematic has this part cutoff, piecing it together I'm wondering if the delay line has opened or a bad solder connection at the base of the tube where the terminal is crimped down, I've seen these open here before. Check the delay line for continuity, it should be several ohms but not a complete open except on one terminal which is an internal shield and grounded. Look at the base of Q1 video amp and do a continuity check from there to the cathode of V4 and you should find another 1200 ohms on top of the delay line. The cathode sets up the bias for Q1 and finds its ground thru R71.
The lack of 3V on the V4 grid coming from the video detector tells me there is a gain issue in the IF amp itself and this is why I question whether one of the IF tubes has been transposed. Check the cathodes of V1 and V3 to verify they are under about 30 volts to ground. Have any of the IF coils A8 thru A11 been touched at all? The slightest change here will have a dramatic effect and require a sweep marker generator to get back on track, same with the chroma coils. I'm speaking from experience here they can be a real pain without the right test equipment. With a good strong IF signal coming into A7/A8 the detector diode will put out well over -3 volts of video signal, plenty enough to drive V4 into cutoff.
I have a Zenith 20YCI37 schematics buried somewhere and will unearth it, they're similar enough for me to help more than hinder. Give me a day to locate and study it for some answers. You have a real gem there and I'd really like to see you get it going.
I wouldn't worry about the line voltages, anything between 115 to about 120V is acceptable to the world of tube TV's

Alright. I spent some time looking at my Zenith 20YC137 print (sams 932/3) as the YC and the XC are similar enough to where I can fill in the blanks.
The issues you have described so far still point strongly to the IF section and I'm wondering if this this is being caused by a gain issue be it voltages running near the cutoff regions of the IF tubes, misaligned coils or the possibility a 6EH7 is occupying V3.

First lets go back to the voltages but instead of just whats there to ground focus on the differentials as these are far more critical.
V1 with 130v on the plate, 27v on the cathode and 24v on G1 according to the Sams, its this 3V differential between K and G1 that is important.
V2 is a special case in that the cathode is on the end of R51/R52 giving it approx 140v with the grid at 135v, 5v difference here while the plate runs at 230v making the tube run at a potential of 90v. Look for the +245v supply coming into R52 as it will have a dramatic effect on the overall IF performance.Find this source on the half circle terminal of C3 in the power supply section as this is derived from the +340V source thru R202 which is a hefty 15-Watt 720 ohm wirewound resistor, a low +245v source will also pull down the +125v source so don't discount the multi-section capacitor.

Low IF might not kill the sound entirely but it will affect the sync and chroma. Sound & sync are derived prior to the video detector, looking at your YouTube post it appears the sync is trying to latch onto whatever is coming thru V6b which again point me to a gain issue upstream.

The voltages of V4 pin-9 and pin-8 are going to be at or near the supply when the tube is in cutoff, its controlled by the color killer detector and with no colorburst coming into the burst amp the killer detector is not going to provide the needed DC to bias the bandpass amp into conduction. Lets forget about the chroma stages at the moment and focus on the why very little is making its way into pin-2 of V4.

Let me know what you find, I will keep my schematic out and handy

Alright. I spent some time looking at my Zenith 20YC137 print (sams 932/3) as the YC and the XC are similar enough to where I can fill in the blanks.
The issues you have described so far still point strongly to the IF section and I'm wondering if this this is being caused by a gain issue be it voltages running near the cutoff regions of the IF tubes, misaligned coils or the possibility a 6EH7 is occupying V3.

First lets go back to the voltages but instead of just whats there to ground focus on the differentials as these are far more critical.
V1 with 130v on the plate, 27v on the cathode and 24v on G1 according to the Sams, its this 3V differential between K and G1 that is important.
V2 is a special case in that the cathode is on the end of R51/R52 giving it approx 140v with the grid at 135v, 5v difference here while the plate runs at 230v making the tube run at a potential of 90v. Look for the +245v supply coming into R52 as it will have a dramatic effect on the overall IF performance.Find this source on the half circle terminal of C3 in the power supply section as this is derived from the +340V source thru R202 which is a hefty 15-Watt 720 ohm wirewound resistor, a low +245v source will also pull down the +125v source so don't discount the multi-section capacitor.

Low IF might not kill the sound entirely but it will affect the sync and chroma. Sound & sync are derived prior to the video detector, looking at your YouTube post it appears the sync is trying to latch onto whatever is coming thru V6b which again point me to a gain issue upstream.

The voltages of V4 pin-9 and pin-8 are going to be at or near the supply when the tube is in cutoff, its controlled by the color killer detector and with no colorburst coming into the burst amp the killer detector is not going to provide the needed DC to bias the bandpass amp into conduction. Lets forget about the chroma stages at the moment and focus on the why very little is making its way into pin-2 of V4.

Let me know what you find, I will keep my schematic out and handy

Good points to think about for sure. Good to be observant of correct looking differentials. Although, scoping out the IF I'm seeing a pretty healthy signal that seems to hit a wall around V4A. Supposed to have 2.5v, 3, 240 respectively and I have .8, 12, 235, so It's not conducting too well...

Feeding composite straight into the video amp or output yields a pretty good pic, minus of course the sync.

I did replace Q1 with a 2n222 which gave me a little improvement but nothing dramatic. I can make out less faint figures and text in the pic now.

BTW, Peak picture, contrast, brightness, and bright range, all ohm out ok.

I cut the ground on the delay line and jumpered it with no improvement.

Will continue analyzing and report back any interesting findings.

Waiting on tubes for subbing, as well.

Another update, and I believe I've solved the mystery. My hunch was correct about V4A, the cathode follower. Waveforms confirmed that that tube section was not conducting sufficiently. Swapping it with V10, appears to have resolved the trouble. This tube tested ok on 2 testers, by the way!

In position at V10, the same problem tube isn't problematic here, apparently because of how it functions differently with the color killer.

Replacing the stock Vid Amp transistor, Q1 with a modern 2N222 and and vid detector with a fresh 1N60 also livened things up a bit.

This is the first set that I've operated on that has a cathode follower. My understanding is that this section provides impedance matching for the delay line (?)

The only truly defective part was the broken degauss thermistor, which I replaced with a NOS one.

......This tube tested ok on 2 testers, by the way!......



There should be a sticky at the top of the homepage with three essential words ;

"Tube Testers Lie"

:D

Tube testers can't really show you what's going on inside, little more than arbitrary numbers however some are better than others. Its a static test that doesn't duplicate the real dynamics of high frequency interactions between the elements or "spot" emissions of the cathode.

There should be a sticky at the top of the homepage with three essential words ;

"Tube Testers Lie"

:D
Best tester is the TV