Currently trying to iron out a smearing issue that appears on high contrast areas, especially text. I believe this in not an uncommon problem, but I've tediously made several attempts to trace the cause with no success so far. I understand this is typically due to problems with open coils or leaky caps in the IF and Video stages...

Example 1: https://i.ibb.co/NWY3Kpz/IMG-3797.jpg

Example 2: https://i.ibb.co/C0hM5HD/IMG-3798.jpg



Some test info and findings:


CRT tests good on emissions, about 1/3 into the good scale on a B&K 465. I don't recall what the cutoff was, but the picture is bright and clear

All tubes in IF section test good and have no shorts and aren't gassy

Performed step one in RCA service guide for peaking (max/min) IF stages with non sweeping frequency and this did NOT affect or remedy the smearing. I assume this stage of alignment is to get your stages "in the ballpark" before further refinement in the sweep gen alignment procedure?

Injected composite video into circuit, just before the 1st Video Amp, and observed smearing, leading me to believe the defective component should be after that stage.

Injected composite video into circuit, just before the 2nd Video Amp, and observed a reversed fainter image, but didn't notice smearing - not that there couldn't have been any, I just didn't see it, leading me to believe offending component to be before this stage.

All peaking coils' in IF and Video tested ok in terms of resistance, cold solder joints. Adjoining resistors were also tested - a couple were out of tolerance and replaced, but did not affect the smearing.

Replaced the video detector diode - no effect.

Replaced coupling caps in these sections - no effect.

Switched the converter box - no effect.

Tested continuity and resistance of Delay Line and noted about 130Ω. Even shorted the delay line to see color shift but no change to the smear.

Saw no cold solder joints on the underside of the IF or Chroma boards.


IF section Sams schematic:
Pt 1 https://i.ibb.co/JcW3hRS/Screen-Shot-2021-05-23-at-10-04-49-AM.png

Pt 2 https://i.ibb.co/pd6hRGz/Screen-Shot-2021-05-23-at-10-05-05-AM.png

Thoughts/questions


One thing that I observed was that when I jumped a couple of the peaking coils there was no effect to the picture. Could this mean that there might be shorted turns in one or more of the coils? I don't have an LCR meter, but I do have a Sencore YF-33 Ringer Yoke FLyback Tester. Not sure yet how to use that to test peaking coils.

Adjusting coils, traps or transformers in the IF/Video stages doesn't affect the smearing

Could it be poor cutoff on the CRT? The CRT is bright and clear though.

Wow, wish everyone worked a problem like this ! Well done.
If you have an anylist break the chain at the video amp & inject
video. This will cut the possible stages in half. Its why I scream
" learn the block diagram" for newbies.
I would not suspect the CRT. Those little square peaking coils
did open but I never saw one short. I am sure you covered it
but be sure all the ground lugs for the PCB's are good & any shielding
like the IF is also.
On the Sencore most of there gear came with 2 manuals. One was
a basic manual & the other was a large book that showed every
creative thing you can do with it. Look into that.

73 Zeno:smoke:
LFOD !

Peaking coils will only affect very short transients, near edges. Not the case here.

That streaking is a very long time constant, lasting for most of a scan line.

The important clues are:

Injected composite video into circuit, just before the 1st Video Amp, and observed smearing, leading me to believe the defective component should be after that stage.
Injected composite video into circuit, just before the 2nd Video Amp, and observed a reversed fainter image, but didn't notice smearing - not that there couldn't have been any, I just didn't see it, leading me to believe offending component to be before this stage.


Scratching my head a bit to identify a component with such a long time constant.

Wish they listed the inductance value of L10, but assuming it's OK, how about R57 220 ohm and C21, .001uf (screen bypass) or C24 and R61 (connect to the sync separator).

Also check C1, 40 uf, in the AGC/sync separator circuit.

Wow, wish everyone worked a problem like this ! Well done.
If you have an anylist break the chain at the video amp & inject
video. This will cut the possible stages in half. Its why I scream
" learn the block diagram" for newbies.
I would not suspect the CRT. Those little square peaking coils
did open but I never saw one short. I am sure you covered it
but be sure all the ground lugs for the PCB's are good & any shielding
like the IF is also.
On the Sencore most of there gear came with 2 manuals. One was
a basic manual & the other was a large book that showed every
creative thing you can do with it. Look into that.

73 Zeno:smoke:
LFOD !

Can you recommend a particular Analyst?

Peaking coils will only affect very short transients, near edges. Not the case here.

That streaking is a very long time constant, lasting for most of a scan line.

The important clues are:

Injected composite video into circuit, just before the 1st Video Amp, and observed smearing, leading me to believe the defective component should be after that stage.
Injected composite video into circuit, just before the 2nd Video Amp, and observed a reversed fainter image, but didn't notice smearing - not that there couldn't have been any, I just didn't see it, leading me to believe offending component to be before this stage.


Scratching my head a bit to identify a component with such a long time constant.

Wish they listed the inductance value of L10, but assuming it's OK, how about R57 220 ohm and C21, .001uf (screen bypass) or C24 and R61 (connect to the sync separator).

All these caps have been replaced. OOT Resistors too. I may have to check C22, the 7pF. Don't recall if I replaced that one.

Next plan is to jump into more extensive voltage testing as well as video insertion. Maybe see if I can trace down to a bad tube pin joint, supply voltage or something overloading a section. Open to other ideas.

All these caps have been replaced. OOT Resistors too. I may have to check C22, the 7pF. Don't recall if I replaced that one.

Such a small cap cannot produce such a long smear. C7 couples only high video frequencies to the chroma circuits.

I would nose around the AGC / sync separator / noise inverter, since feedback circuits can do weird things and make it difficult to figure out where in the loop the problem is. Check voltges in that area, and substitute V6 if you have a spare. The fact that the smear disappears when you couple to the 2nd video is a strong indication that the problem is in first video or the above stuff that is fed from the first video.

Since the smear starts on black lettering, it's possible the AGC circuit is conducting during trace when it should be gated off. It would be good to know that the 450 volt keying pulse on pin 9 of V6 is there, as well as whether V6 is good.

Also, in case the smear really is still there when you inject into the second video, check any caps in the following video circuits that are .01 uf or larger.

You didn't say you have a scope - this is a case where looking for the right waveforms could be much faster to isolate the problem.

My CTC-16XL does the same thing, but to a MUCH lesser degree, it's hardly noticeable on mine, but it is there, it seems that it's common, but not sure what the cause is.

Voltage tests on V4 indicate wrong voltage on pins 7, 8 and 9.

pin7: -5 vdc / .5 vac / Should be 0 vdc and 3.5 vac

pin 8: 177v / Should be 95v

pin9: 184v / Should be 130v

Resistances are wrong on pin 7 to B+ output according to the Sams.
Pin 7: 2.1kΩ and 3.4kΩ (Sams states R depends on polarity of probes)
R should be 130Ω

So, something's overloading the grids and plate on the Vid1 section and the tube can's cut off correctly. I have some ideas suspect dropping resistors and DC blocking caps before the Vid 1 stage, maybe even going back to the AGC...

Will also bust out my scope to verify the waveform on the Vid input. Maybe try different video injection points. I don't have an analyzer, so I have to do it by composite from the set top box.

For pin 8 to be 177, the 100 v source that feeds it must be way too high. Check all the power supply voltages (but especially the 100 v source and R215, 47k 1W) and check pin 8 again to make sure you read it right.

Pin 7 should be 0vdc as you state. However, the 3.5 V on the schematic is not an ac meter reading but a scope peak-to-peak reading of the video waveform. AC meter reading will vary drastically depending on video content. The 30~ notation means the scope sweep rate is set to 30 Hz, so you see the two video fields as illustrated.

Where do you see that the resistance reading for pin 7 should be to B+? I think it should be 130 ohms to ground, and the note on polarity variation is because of the video detector diode.

Where do you see that the resistance reading for pin 7 should be to B+? I think it should be 130 ohms to ground, and the note on polarity variation is because of the video detector diode.

correct, it is to ground,

as stated on page 8 of the SAMs

it does not say anyplace that its to be from b+

Where do you see that the resistance reading for pin 7 should be to B+? I think it should be 130 ohms to ground, and the note on polarity variation is because of the video detector diode.

I think I got this confused I think with another measurement. It is to ground. The same measurements still stand

For pin 8 to be 177, the 100 v source that feeds it must be way too high. Check all the power supply voltages (but especially the 100 v source and R215, 47k 1W) and check pin 8 again to make sure you read it right.

Pin 7 should be 0vdc as you state. However, the 3.5 V on the schematic is not an ac meter reading but a scope peak-to-peak reading of the video waveform. AC meter reading will vary drastically depending on video content. The 30~ notation means the scope sweep rate is set to 30 Hz, so you see the two video fields as illustrated.

Great information. I really appreciate it.

correct, it is to ground,

as stated on page 8 of the SAMs

it does not say anyplace that its to be from b+

Got it switched with a different measurement...hard to keep track sometimes. I keep a journal, but I didn't note that

Got it switched with a different measurement...hard to keep track sometimes. I keep a journal, but I didn't note that

you can see my baby here !
https://www.youtube.com/watch?v=7V3etX2NsS4

:)

Resistance from pin 7 to ground with detector diode reveresed should be essentially R54 and R55 in parallel = 3327 ohms. This agrees with your measurement.
With the opposite polarity, it will depend on how much voltage your meter applies to the circuit to measure resistance, which will determine how much the video detector diode conducts. I suspect your meter has a lower voltage than the one SAMS used. So 2.1 k may be fine.

The DC voltage on pin 7 will depend on video content, and will be more negative with a dark scene, so -5 volts *may* be OK too. Have you checked L6?

It's a shot in the dark, but just for the heck of it, try subbing the 3rd IF tube. On multiple occasions, I've had the 3rd IF cause ringing/smearing effects (albeit not of the duration yours has). This was even tho the tube tested 'good'.

I agree, the 100v may be way too high, there are only 2 things tied to that, 1st video and V6 agc pin7 which may also may be too high (point 21) , for that matter, 315v may ALSO be too high, being tied to only 1 connection, you just may not be seeing any symptoms of it, meaning that R213 may be to blame.
You may want to check the voltages on the entire divider tree to be safe.

you can see my baby here !
https://www.youtube.com/watch?v=7V3etX2NsS4

:)

Dig it!

OK, finally set aside some time to further troubleshoot, take some waveforms, and voltages. All peaking coils' continuities test good. Pretty much replaced all larger value caps in the video agc sections and no change. Checked all grounds again and they appear fine.

Voltage checks on V4 ok except pins 8 and 9 which were about 70 and 50 v too high, respectively.

Voltage checks on AGC V6 appear ok, except maybe pin 7 which was about 10v high. I need to mull over this data to figure out what it means, but I think there's a connection between the AGC (as someone else may have alluded to earlier) and the 1st video stage...

Pin 2, V4. Video is reversed here, but not very much noticeable smearing, as opposed to the first stage of V4. Hard to lock the picture due to lack of sync when injecting video at this stage.
https://i.ibb.co/6RZ5DFc/IMG-3844.jpg
https://i.ibb.co/kXWVBQ9/IMG-3846.jpg
https://i.ibb.co/gDYj7QR/IMG-3849.jpg

Some waveforms, starting with the AGC. All appear to look normal to me.
Pgs 2 and 3 can be referenced for the waveforms here: https://earlytelevision.org/pdf/rca_ctc16x_sams-0818-2.pdf

https://i.ibb.co/Hgn5JS0/IMG-3853.jpg
https://i.ibb.co/4fLFfPq/IMG-3854.jpg
https://i.ibb.co/hKFzqZM/IMG-3856.jpg
https://i.ibb.co/9g5YWR5/IMG-3858.jpg
https://i.ibb.co/72rb5C5/IMG-3859.jpg

It's a shot in the dark, but just for the heck of it, try subbing the 3rd IF tube. On multiple occasions, I've had the 3rd IF cause ringing/smearing effects (albeit not of the duration yours has). This was even tho the tube tested 'good'.

I've switched all of the video and sync tubes 2 or 3 times. Unfortunately no change.

All the waveforms from V4 and V5 look like they have a bunch of intermittent spikes where sync should be?? Not sure what I'm looking at. What was the video signal, and was it coming through the antenna?

All the waveforms from V4 and V5 look like they have a bunch of intermittent spikes where sync should be?? Not sure what I'm looking at. What was the video signal, and was it coming through the antenna?

Yes, the signal was RF coming thru the antenna terminals. I think the resolution isn't the greatest on the little Tek 224, maybe why it appears that way? Might need to go back over with my big Tek.

Voltage checks on V4 ok except pins 8 and 9 which were about 70 and 50 v too high, respectively.

Voltage checks on AGC V6 appear ok, except maybe pin 7 which was about 10v high. I need to mull over this data to figure out what it means, but I think there's a connection between the AGC (as someone else may have alluded to earlier) and the 1st video stage...

What's totally puzzling is that the 100v and 390v rails going to V4 test ok

that scope is a perfect example of why i prefer analog o-scopes over digital, especially with that one's low sample rate, it's hard to see anything useful for anything like video. :(

... I think the resolution isn't the greatest on the little Tek 224, maybe why it appears that way? Might need to go back over with my big Tek.



If it's a sampling rate problem (missing sync pulses) in those photos, switch to back to 20 us / Div and view at the horizontal rate. That would be better for looking for the smear, anyway.

How about applying a fixed DC bias to the AGC to see if the smear goes away?

How about applying a fixed DC bias to the AGC to see if the smear goes away?

Where? Point A in the Sams schematic, where it indicates to apply bias for an alignment? Tried that -15v on down to zero and video disappears. Another point perhaps?

Not sure - there may be a conflict between tuner AGC and IF AGC that makes my idea not work.

Measure the voltage on point A with the set running normally, then apply the same DC voltage, and see if that works.

Posted voltages will always vary from set to set to some degree, so the higher voltages you are seeing may, or may not be an indication of anything :(

But to go and jump into a pool of redundancy, and state the obvious, I'm sure you have already checked things like R56 R57, R74-76? The usual drill? :)

Posted voltages will always vary from set to set to some degree, so the higher voltages you are seeing may, or may not be an indication of anything :(

But to go and jump into a pool of redundancy, and state the obvious, I'm sure you have already checked things like R56 R57, R74-76? The usual drill? :)

Yeah, all those resistors are within spec...

Good point on the inconsistency of voltages between sets. Also, currents can be altered by pot settings and whatnot, so...

I was reading your long troubleshooting thread about your set. Overall, what were your findings, from a high level? I saw that you were buying and subbing peaking coils and what not. What were your conclusions?

Yeah, all those resistors are within spec...

Good point on the inconsistency of voltages between sets. Also, currents can be altered by pot settings and whatnot, so...

I was reading your long troubleshooting thread about your set. Overall, what were your findings, from a high level? I saw that you were buying and subbing peaking coils and what not. What were your conclusions?

That's on the future “to do” list, to try and address the minor annoyances that are still there in my set, like replacing L13, that may or may not be damaged by the person who had it before me, re-do the grounding of the delay line so it's more OEM spec, replace the worn R131 (66meg 6kv) to get more focus range, check & most likely replace R70 , R71, C31, to try and get better blanking, check for any other leaky caps in the video output area, there is minor background shadowing with bright logos against darker backgrounds, but this may be normal/ unavoidable, as I have it in A/V bypass, the IF still needs alignment, but I don't have the tools for it, it WILL WORK, but has red smearing, so I have a signal relay at L9 and C53, and can go from tuner or A/V with a flip of a switch!

Really the only things that are left that could be suspect would be disc caps and the remote possibility that there is a shorted peaking coil. All mylars that were in these circuits in question have been replaced, and frankly when tested out of circuit, they were still within spec and not very leaky. I'm reluctant to pull the chassis out again. Wires can only stand so much of that, especially the tuner that's separate, but hard wired, and has to be moved with the main chassis.

I actually have peaked the coils again and the picture is decent enough. I don't need it to be a reference model or intend for it to be a daily watcher. The flyback wouldn't be able to take that, unless I mod the cage for ventilation.

It could probably use a full setup again and a full alignment, which I may start this weekend, but I may wait to get a hold of a better marker generator (don't have one...only the marker on my sweep gen and an additional freq gen...would like to access all at the same time rather than having to punch each one up.) If anything, I'm curious as to how screwed the bandwidth shape is.

If pin 7 is at -5v as you said early on, then the first video amp
tube v4 is close to cutoff. Cutoff is where the tube does not
conduct any current, that would explain the high voltages
on the plate & screen grids. I would wonder if the 22ohm
resistor in the cathode circuit is open? or there is a
bad connection, broken foil etc. Why is -5v on pin
7? bad resistor to ground up stream closer to
the detector? For the most part the picture looks
good, and you have color, so it's all pretty much
working. So it's gotta be a little thing......

If pin 7 is at -5v as you said early on, then the first video amp
tube v4 is close to cutoff. Cutoff is where the tube does not
conduct any current, that would explain the high voltages
on the plate & screen grids. I would wonder if the 22ohm
resistor in the cathode circuit is open? or there is a
bad connection, broken foil etc. Why is -5v on pin
7? bad resistor to ground up stream closer to
the detector? For the most part the picture looks
good, and you have color, so it's all pretty much
working. So it's gotta be a little thing......

Yep, not only the voltage on pin 7, but 8 and 9 are way out of spec from the schematic. R56, 22Ω is within spec too. The 100v and 390v rails measure correctly. I replaced R58, 10k/10w even though it measured in spec out of circuit. I agree, as you said about the -5V on pin 7 producing the voltages on 8,9. That points to a possible problem upstream.

The only route to pin7 on V4 is thru the vid detector, via V3. The 200V rail that feeds the grid on V3 measured ok, but looks like I need to dig deeper and check around V3 for voltages carrying the IF signal thru the detector.

Q. - If you disconnect the signal to antenna do you get snow
on the screen? w/ or wo color? and do you get snow on sound?
if no, then you know where you need to go also. if yes then
I'm not sure I would go to AGC right now.
R56 that 22ohm job, do you have a good unbroken connection
from the tube pin through the socket, through the PC Foil to
the resistor wire 100%? You probably need to poke around
everything in the detector area, DC Scope readings on both
sides of the detector? do they seem right? Something out
of place in the signal? And yes use a real analog scope.
and stop turning coils, you could be tuning for that
streaking and making it worse. Never do that to a
tv or radio with a problem.

Q. - If you disconnect the signal to antenna do you get snow
on the screen? w/ or wo color? and do you get snow on sound?

A. This is what I get (minus the camera blanking bar) and no, I don't get snow on sound. I tested the mixer tube and I believe that was good. Don't know about the nuvistor...do they go bad? How would something in the tuner affect video and cause smearing?

https://i.ibb.co/y8sjpWJ/1.jpg

if no, then you know where you need to go also. if yes then
I'm not sure I would go to AGC right now.
R56 that 22ohm job, do you have a good unbroken connection
from the tube pin through the socket, through the PC Foil to
the resistor wire 100%?

I'll double check the path to the 22k and scope around more with my analog tek.

You probably need to poke around
everything in the detector area, DC Scope readings on both
sides of the detector? do they seem right? Something out
of place in the signal? And yes use a real analog scope.
and stop turning coils, you could be tuning for that
streaking and making it worse. Never do that to a
tv or radio with a problem.

Q. - If you disconnect the signal to antenna do you get snow
on the screen? w/ or wo color? and do you get snow on sound?

A. This is what I get (minus the camera blanking bar) and no, I don't get snow on sound. I tested the mixer tube and I believe that was good. Don't know about the nuvistor...do they go bad? How would something in the tuner affect video and cause smearing?

https://i.ibb.co/y8sjpWJ/1.jpg

if no, then you know where you need to go also. if yes then
I'm not sure I would go to AGC right now.
R56 that 22ohm job, do you have a good unbroken connection
from the tube pin through the socket, through the PC Foil to
the resistor wire 100%?

I'll double check the path to the 22k and scope around more with my analog tek.

You probably need to poke around
everything in the detector area, DC Scope readings on both
sides of the detector? do they seem right? Something out
of place in the signal? And yes use a real analog scope.
and stop turning coils, you could be tuning for that
streaking and making it worse. Never do that to a
tv or radio with a problem.

wait a sec...
did you just say you DON'T get hiss with no signal input?
I'm not sure what you mean by " and no, I don't get snow on sound."

If by that you mean no hiss, then you are in major weirdsville, cause you SHOULD!

even mine with the messed up IF does.
As seen here showing my weird power down Audio quirk.
https://www.youtube.com/watch?v=Oaw7LDRBB5c

IF you don't get hiss, then you have a lot more going on then just video.

wait a sec...
did you just say you DON'T get hiss with no signal input?
I'm not sure what you mean by " and no, I don't get snow on sound."

If by that you mean no hiss, then you are in major weirdsville, cause you SHOULD!

even mine with the messed up IF does.
As seen here showing my weird power down Audio quirk.
https://www.youtube.com/watch?v=Oaw7LDRBB5c

IF you don't get hiss, then you have a lot more going on then just video.

Nope...literally no static/whoosh sound with no RF in.

Tested the path from V4 to R56 to ground and it's clear. Sure the resistor is 24Ω, but in spec.

Just tested the nuvistor, btw and although the emissions were good, and there were no shorts, my Mighty Mite VI showed grid leakage on the 6DS4.


Funny turnoff sound you got there. I have a couple of electric organs that do a similar thing.

that is a very strong sign that the front end is messed up...

Have you checked R60 & R216 and the voltage on
pin 2 of V4? I bet that +5volts is a bit higher?
That higher voltage on your AGC tube pin 7
of V6, 20V is higher because it's coming
from the plate of V4, so it's to be expected.
with the antenna not connected, no signal
do you still get -5v on V4 pin 7? If yes, you
might just have a noise source being
rectified through the V det. Until you
can figure out that -5V I'm not entirely
sure you have an AGC problem.
But the no Snow condition
certainly points that way.
It's a Conundrum for
sure.



.

Check the two resistors that make up the voltage divider feeding the grid of the 6GM6 second IF tube. Should be 150K or 180K. This was a very common problem of no snow/hiss off channel. This diagram shows them as R306A and B.

Check the two resistors that make up the voltage divider feeding the grid of the 6GM6 second IF tube. Should be 150K or 180K. This was a very common problem of no snow/hiss off channel. This diagram shows them as R306A and B.

correct, R48/R50 they were bad on mine when I started, and got just blank raster.

correct, R48/R50 they were bad on mine when I started, and got just blank raster.

What was the difference in picture quality, once these were replaced?

Check the two resistors that make up the voltage divider feeding the grid of the 6GM6 second IF tube. Should be 150K or 180K. This was a very common problem of no snow/hiss off channel. This diagram shows them as R306A and B.

Checked in circuit, they measure 93k each, which looks consistent with a parallel arrangement.

What was the difference in picture quality, once these were replaced?

i was unable to tune in anything before they were replaced the IF was DEAD

Checked in circuit, they measure 93k each, which looks consistent with a parallel arrangement.
you must remove them to check them correctly

EDIT

if you have not replaced them yet, do it NOW, as someone once once told they will ALWAYS be bad, and/ or out of spec.
this proved correct in my ctc-16 and GE ctc-15 clone, I put 1w parts.

OK, so a couple readings and waveforms with the analog scope today.

Double checking pin 7, V4...
With video: 0v
Without: -3.6v

Scope:

B4 V det:
https://youtu.be/7qv-o0B_aHU

After V det:
https://youtu.be/GdDLbR7zWb0

Pin 7, V4
https://youtu.be/XtraunfLyd4

Pin 2, V4
https://youtu.be/Yiq7CfYEB8s

Replacement Nuvistor ordered, as the current one has bad grid leakage. Just a hunch, there may be excessive noise coming in from the tuner AGC because of this, combined with the boost voltages applied later in the IF, could be distorting the video waveform at some point.

To get clearer scope traces:

Set horizontal sweep to 10 us / div. This will display somewhat more than one video line period (=63.5 usec)
Set vertical gain to calibrated position so you are not reading an unknown amplitude such as > 1 v/div ("greater than").
Adjust trigger level to trigger on H sync pulses

All you can tell from what you have posted is that you have video (but you knew that because you have a picture).

Then, if you can put up a still image that shows the white smear following a black block on a plain background, you may be able to see it on the scope, and see which places in the circuit it appears. If you don't have any test pattern sources, try to find a DVD that shows the problem when you pause it.

Edit: A still image will also allow you to see the effects of any adjustments without getting confused by varying video content.

Another hint: for pin 7, you should set your scope to DC coupling and establish where 0 volts is on the scope screen with the vertical centering control. Then you can see the actual voltage range on the grid.

Some things I don't understand right now:
Why is the DC on pin 7 zero volts with video? The detector diode is working negative with respect to ground, so any IF signal should pull the grid negative.

Why does pin 7 go negative with no video (I assume you mean no RF signal?). Does the scope show a lot of random noise there with no RF? If so, and you don't see snow on the screen, this would mean the tuner and IF are fine and something is causing the noise to be suppressed before it gets to the output (perhaps the noise inverter).

Thanks for posting scope videos, feel free to post 1 or 2 full
minutes of tape in the future. In your first 2 videos it sure
looks like there is a lower frequency noise floating through
the semi-synced picture. While looking at a longer scope
run, you should sweep the sweep speed setting and see
if you can capture the noise. The last one looks more
normal. With that V4 Pin 7 voltage back to 0V with
video I think you should replace those 2 resistors
mentioned above. You can expect in circuit
resistance measurements to be somewhat
accurate if the value of the resistor is
.5 Ohms to possibly 20K. Anything
over 100K you should expect a 90%
chance of complete inaccuracy.
You might also want to at this point
check out that entire AGC line back
to the tuner. From those 2 resistors
R 48 & R 50 keep going back to
the tuner, & check that .5V at
the end of that line. See
what you get.


.

Yes, I also expected a different voltage at pin 7 with no video.
he needs to slow the sweep and try and find that noise.
It may even be heater to cathode noise getting into
the detector.


.

Correct me if I'm wrong, but didn't the OP figure out that the smearing is there if he injects video at the first video amp and gone if he injects it at the second video amp?
If that's the case he should fix it so that he can get smear free video when injecting at the output of the video detector before worrying about the front end and IF sections.
I'm not saying the front end doesn't have issues, but if there's issues in the video stages too then they will hide any progress or other issues in the front end and IF stages.

When you have multiple problems in a TV there's often an optimal and a counter-productive order to tackle them in.

A lot of good feedback and apologies for my crude scope pix.

And, ok ok you've twisted my arm on the 2 resistors. Just about every resistor I've pulled from that set has been reasonably within spec, but maybe those 2 just get an unusual hammering for some reason, so I'll take a closer look.

From Sam's TV Servicing Guide

https://i.ibb.co/MnSs2cR/Sams-TV-Servicing-Guide-Smeared-1.jpg

https://i.ibb.co/XV71KfP/Sams-TV-Servicing-Guide-Smeared-2.jpg

https://i.ibb.co/w7p050H/Sams-TV-Servicing-Guide-Smeared-3.jpg

https://i.ibb.co/Jz14jZV/Sams-TV-Servicing-Guide-Smeared-4.jpg

No progress on this yet. Been busy with my other set. Ordered a cheap function generator kit for a square wave to quickly test response through the IF and Video.

No progress on this yet. Been busy with my other set. Ordered a cheap function generator kit for a square wave to quickly test response through the IF and Video.

You can't align video IF with a square wave generator. You need a TV specific Sweep and Marker generator.

That TV video IF response curve that looks like a square wave with peaks on the ends is not created by injecting a square wave into the TV. It's created by an IF sweep generator.

An IF sweep generator is essentially an an overcomplicated radio alignment generator.
It generates a wine wave frequency in the TV IF range and contains a 60Hz ramp wave generator the ramp wave modulates (sweeps) the IF output frequency from around 3MHz below the center to around 3MHz above it. So the sweep generator outputs a constant amplitude RF signal (the frequency of which constantly changes such that it sweeps the entire IF passband at roughly 60Hz), and the 60Hz signal is also output. The 60Hz feeds the horizontal axis of the oscilloscope, and the vertical axis of the scope is fed from a demodulator probe connected to the TVs IF.
Basically the sweep generator and the scope form an RF curve tracer (or primitive RF network analyzer if you are familiar with RF network analyzers) that traces the IF response on screen by feeding the TV IF input a constant amplitude signal that sweeps it's frequency response range, sweeping the scope horizontal in sync with the frequency and ploting the non-constant output (which is the response curve) on the scopes vertical axis.

A marker generator is basically an RF wine wave generator with very precise frequency. TV specific ones can create multiple marker frequencies simultaneously and usually use crystal oscillators. You can use a modern digital RF generator or even an old tube radio RF generator (and a modern digital frequency counter to precisely adjust it) instead or in addition to a TV specific marker generator.
The marker generator adds extra fixed frequency energy to the signal injected into the TV IF creating a thing vertical line above and below the response curve on the scope to tell you if your response peaks are at the right frequency (because the sweep generator sacrifices frequency precision/accuracy to perform the sweep).

If alignment is a complex involved process that requires a lot of specialized equipment, knowledge and practice (it's nearly as much art as science) to do well.

You can't align video IF with a square wave generator. You need a TV specific Sweep and Marker generator.

That TV video IF response curve that looks like a square wave with peaks on the ends is not created by injecting a square wave into the TV. It's created by an IF sweep generator.

An IF sweep generator is essentially an an overcomplicated radio alignment generator.
It generates a wine wave frequency in the TV IF range and contains a 60Hz ramp wave generator the ramp wave modulates (sweeps) the IF output frequency from around 3MHz below the center to around 3MHz above it. So the sweep generator outputs a constant amplitude RF signal (the frequency of which constantly changes such that it sweeps the entire IF passband at roughly 60Hz), and the 60Hz signal is also output. The 60Hz feeds the horizontal axis of the oscilloscope, and the vertical axis of the scope is fed from a demodulator probe connected to the TVs IF.
Basically the sweep generator and the scope form an RF curve tracer (or primitive RF network analyzer if you are familiar with RF network analyzers) that traces the IF response on screen by feeding the TV IF input a constant amplitude signal that sweeps it's frequency response range, sweeping the scope horizontal in sync with the frequency and ploting the non-constant output (which is the response curve) on the scopes vertical axis.

A marker generator is basically an RF wine wave generator with very precise frequency. TV specific ones can create multiple marker frequencies simultaneously and usually use crystal oscillators. You can use a modern digital RF generator or even an old tube radio RF generator (and a modern digital frequency counter to precisely adjust it) instead or in addition to a TV specific marker generator.
The marker generator adds extra fixed frequency energy to the signal injected into the TV IF creating a thing vertical line above and below the response curve on the scope to tell you if your response peaks are at the right frequency (because the sweep generator sacrifices frequency precision/accuracy to perform the sweep).

If alignment is a complex involved process that requires a lot of specialized equipment, knowledge and practice (it's nearly as much art as science) to do well.

No, this isn't for alignment. My BK 415 will be for that. This is a quick test procedure to check video response (for troubleshooting/location of bad component)

Here's an illustration
https://ibb.co/Z2FH3TQ