Tele-tone TV 149 video trouble needing help.

[cameronflyer]

Hi guys, I've been working on this Tele-tone off and on for a couple of weeks now. I have perfect sound, all the voltages seem to be correct. I have checked and rechecked all the resistors and caps, replace a lot of out of tolerance resistors. But I still do not have a viewable picture.I am going to attach a couple of photos and a link to a YouTube video I would appreciate it any help you guys can give me. https://www.youtube.com/watch?v=ze0S5Sb5_9s

[Tom Albrecht]

Since you have very good sound, and this set uses intercarrier sound, it seems like the video IF has to be working on some level, and the video amp. That doesn't leave very many components that could be giving a problem. Check the wiring and components around the video amp stage and the route for the signal from that stage to the CRT cathode. Make sure the coils on L14 and L15 (in SAMS) are not open. Is the brightness control working properly? Does the contrast control have any effect?

Also, have you adjusted the fine tuning oscillator coil slug in the tuner for the channel you are using?

[Electronic M]

Might want to check the video detector diode (if SS type) too.

[cameronflyer]

Thanks for the info, I haven't checked the coils I'm sorry to say. I will check them as soon as I get back to the shop. As for the detector, I have replaced it with a NOS. And the tuner coil has been adjusted. I am truly at a loss on this one folks. One thing that puzzled me was the 2 6al5 tubes both read low on my tube tester, as well as the 5 others I have on hand. Maybe my tester is off a bit? But I did recently recalibrate it.

[vts1134]

Suggesting the rediculously obvious because I've been there in the past so take no offense, is the detector diode backwards?

[cameronflyer]

No offence taken , the detector is a vacuum tube type so backwards isn't possible. The brightness works just fine, but the contrast affects thee sound like a tone control with little affect on raster if that tells you anything.

[Tom Albrecht]

That all seems to point to the very few components between the video amp plate and the CRT cathode. just a few inductors, capacitors, and maybe a resistor. Those coils would be at the top of my list, as would the 0.25 uF cap which should be coupling the signal from the plate of the video out to the CRT cathode.

[edison64]

just wondering if you changed out several of the caps that are under the high voltage section, not the ones on the bottom of the chassis these are actually on a circuit board mounted underneath the 1b3 tube socket.

[cameronflyer]

Because the HV section is kind of hard to get to, I shotgunned the entire circuit in the very beginning. Including all resistors and caps.

[Username1]

It looks like you replaced all the caps. And in yer video you can hear noise in the sound
as the scene changes, I'm wondering if each stage needs to be re-tuned.... Can you pick
good waveforms out along the way...? Or do you have a way of injecting signal along
the way....?

.

[old_coot88]

I was completely flummoxed one time, chasing a no-video problem (Maggie color set). Sound and chroma were fine, but absolutely no luma at all. Chased the video amp stages, everything downstream of the v.detector, 'round in circles for a week. But no cigar.

After much hair-pulling, it finally occured to look at the video IFs. Sure enuff, the 2nd v. IF stage was dead. Yet the sound and chroma subcarriers were going thru by pure capacitive coupling, with no discernable attenuation.

Moral of story was to not overlook the v. IFs when there's no video but sound is still good (on an intercarrier set).

[cameronflyer]

Vaveforms were my next stop on this journey. I have to unpack my test leads when I get done with work today.

[earlyfilm]

Originally Posted by cameronflyer

Vaveforms were my next stop on this journey. I have to unpack my test leads when I get done with work today.

Frankly if it were my set, I'd do it with a redneck signal injector!

Take a small 600v capacitor, say an .005MF and hold one lead in your hand and touch the other end to the cathode (the video is cathode injected in this set) of the 7JP4 CRT and you should get a 60 cycle hum in the picture. If it is very weak, try reversing the AC plug, as that either will increase or reduce it.

Then follow the signal back to the plate of the 6AU6 Video AMP, and then to the grid of the same tube.

Then go to the plate pin 7 of the 6AL5 Video detector, and then to pin 1, the cathode.

The 60 cycle hum your body is picking up should modulate the IF stages, too, so follow it back.

You are looking for the point where the signal disappears, which sure makes finding the problem easier.

When the hum gets too strong, switch to a much smaller capacitor.

(If the signal is too strong, it may jump the defect.)

Oh, and remember this is a hot chassis set, so use due care.

Back in the late 1950's when I was servicing TVs, I used to keep several value small caps with a brass washer soldered on one end hung up on a nail above my workbench, just for this purpose. I covered the lead between the cap and the washer with spaghetti to lessen the chance of an accidental contact with the set.

James

[Username1]

Yah ! do what he said ! ! !

.

[DaveWM]

I had a set like that, it had been recapped before I got it. turned out one of the coupling caps was attached to the wrong term on a term strip that fed the video amp tube. Like the ohters have said I would go with a video injection to isolate the loss of the signal. I use a BK 1076 video analyst.

here is a video of the defect I found.
https://www.youtube.com/watch?v=qkJ3...CVtyRrqXVtll-g