RCA CTC-16XH Smearing Issue
 

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...0-04-49-AM.png

Pt 2 https://i.ibb.co/pd6hRGz/Screen-Shot...0-05-05-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.

Can you recommend a particular Analyst?

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.

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.

correct, it is to ground,

as stated on page 8 of the SAMs

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

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

Great information. I really appreciate it.

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.

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_...ams-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

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?

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. :(

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?

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? :)

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......

Quote:

Originally Posted by Username1 (Post 3234194) 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.