RCA CTC-16XH Smearing Issue

[Jon1967us]

Originally Posted by old_tv_nut

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?

[old_tv_nut]

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.

[Yamamaya42]

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?

[Jon1967us]

Originally Posted by Yamamaya42

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?

[Yamamaya42]

Originally Posted by Jon1967us

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!

[Jon1967us]

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.

[Username1]

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......

[Jon1967us]

Originally Posted by Username1

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.

[Username1]

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.

[Jon1967us]

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?



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.

[Yamamaya42]

Originally Posted by Jon1967us

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?



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.

[Jon1967us]

Originally Posted by Yamamaya42

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.

[Yamamaya42]

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

[Username1]

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.



.

[damen]

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.