How to inject a signal into a TV?

[wa2ise]

Video signals have a polarity, and you can have it be upsidedown. Not upsidedown as if the vertical yoke were wired backwards, but the video looking like an old fashioned photographic negative. Whites being black, blacks being white, and so on. Also the sync circuits won't sync up.

[maxhifi]

I think that in addition to what has been said already, one thing which may be valuable is to use an oscilloscope to view the "normal" waveforms at each point for a Properly operating tv, side by side with the service manual (one of the RCA manuals which shows waveforms would be ideal) section by section.

Once you know what waveforms should be where, then it's the right starting point for reading the manual for the B&K

[old_coot88]

Originally Posted by wa2ise

Video signals have a polarity, and you can have it be upsidedown. Not upsidedown as if the vertical yoke were wired backwards, but the video looking like an old fashioned photographic negative. Whites being black, blacks being white, and so on. Also the sync circuits won't sync up.

(For any noobs' benefit), phase inversion occurs because a tube's plate is 180 degrees out of phase with the grid. I.e., grid goes positive, tube conducts more, plate voltage drops. Then grid goes negative, tube conducts less, plate voltage rises.

[ChrisW6ATV]

Originally Posted by wa2ise

Video signals have a polarity, and you can have it be upsidedown. Not upsidedown as if the vertical yoke were wired backwards, but the video looking like an old fashioned photographic negative. Whites being black, blacks being white, and so on. Also the sync circuits won't sync up.

While recently testing my RCA CTC-4 chassis, I saw exactly these results. I injected video just past the video detector diode from my Sencore VA62 Video Analyzer, which has a drive control that varies from several volts positive, through zero, to several volts negative. I could see the unsynchronized, reversed video in the positive direction, and correct video in the negative direction that increased in contrast and synchronized as I increased the negative signal voltage.

[Jon1967us]

Raising this thread again to ask...If I want to inject video from a set top box, can I use the F connector/coax from the box or should I use an rca coming from the composite yellow jack on the box?

[Yamamaya42]

Originally Posted by Jon1967us

Raising this thread again to ask...If I want to inject video from a set top box, can I use the F connector/coax from the box or should I use an rca coming from the composite yellow jack on the box?

the composite yellow jack on the box.

the F connector is modulated output
https://antiqueradio.org/A-V_AdapterForVintageTVs.htm

[Jon1967us]

Originally Posted by Yamamaya42

the composite yellow jack on the box.

the F connector is modulated output
https://antiqueradio.org/A-V_AdapterForVintageTVs.htm

Thx for the tip. I tried my pattern gen and composite out from my converter box and and it worked. I'm trying to isolate where smearing is being produced in the video chain, on my CTC-16XH. Fed the signal into the 1st Vid amp and there was smearing. Fed into the 2nd, and although the image was reversed, I didn't see evidence of it at that point, so I think it's between those two points, probably due to a leaky coupling cap...3.4pF(?)...

[old_tv_nut]

Those little (few pf ) caps don't get leaky, but could open (though not likely). More likely failures are the coils L10, L11, L12. Check L12 resistance to see if it is open. Should read 9.5 ohms, but if open, will read the 10k parallel resistor.

Edit: hope we are both reading the same schematic (rca_ctc16x_sams-0818-2.pdf).

[Jon1967us]

Originally Posted by old_tv_nut

Those little (few pf ) caps don't get leaky, but could open (though not likely). More likely failures are the coils L10, L11, L12. Check L12 resistance to see if it is open. Should read 9.5 ohms, but if open, will read the 10k parallel resistor.

Edit: hope we are both reading the same schematic (rca_ctc16x_sams-0818-2.pdf).

Yep, Sams 818.
Measuring 25k across coupler C23. Need to lift a leg and get a real measurement on that little cap. The coils you mentioned are underneath the board. Hopefully they're not bad, as only a parts chassis could supply a replacement. L12 is after my injection point that didn't show smearing. So, yeah, L10, 11, C23 or a drifted R60...

[TV-collector]

There is another way to inject a signal.
The german "Funkschau" offered in the 50s a nice DIY-device.
This little assy covers a tube "EC 92", father & mother socket for the CRT,
and a few resistors, caps, 2 switches, cables and a piece of alloy.

It is a little generator which produces horizontal and vertical bars.
The device gets its voltages from the CRT plug.

To operate it, it has to be pushed on the CRT contacts and the plug coming from the TV chassis is conected with the backside of the assy.

Now you can switch beween vertical and horizontal bars on the screen,
as far the voltages to power a CRT are all there.

Regards,
TV-collector

[Notimetolooz]

TV-Collector, sounds like this device. About have way down the page.
Made by Crest Laboratories in the 1940s.
https://www.earlytelevision.org/post...equipment.html
It wouldn't help finding a problem in the video circuits however.

[Tom9589]

Anybody got a schematic for this device?