RCA CTC-16XH Smearing Issue

[Jon1967us]

Originally Posted by old_tv_nut

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

[Jon1967us]

Originally Posted by old_tv_nut

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.

[Jon1967us]

Originally Posted by Yamamaya42

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

[Yamamaya42]

Originally Posted by Jon1967us

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

[old_tv_nut]

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?

[old_coot88]

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'.

[Yamamaya42]

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.

[Jon1967us]

Originally Posted by Yamamaya42

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

Dig it!

[Jon1967us]

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.




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

[Jon1967us]

Originally Posted by old_coot88

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.

[old_tv_nut]

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?

[Jon1967us]

Originally Posted by old_tv_nut

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

[Yamamaya42]

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.

[old_tv_nut]

Originally Posted by Jon1967us

... 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.

[old_tv_nut]

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