While I can understand the IF but what happened here today I still think there is something shorted possibly to ground maybe a cap that I didn’t change yet there are caps still in there originals because on the bench the hv jumped instantly as if there was an arc and at the same time the voltages jumped up on the IF but it was instant a bad alignment would not do this hv jumped 4kv and the IF 15v so I’m going to hope to find this it could be anywhere and besides the picture has flickered in clear on it own several times already so I don’t think the IF is out. I have no idea how I’m going to find this because other then the agc pot not working probably because it’s maxed already trying to fix the signal all other controls work even though something could be leaking somewhere or to ground. I’m sure it wouldn’t take much to corrupt the video signal. So bottom line is voltage still dips diode gets hot so something is not right. I have 2 4 amp diodes I tried they only get warm so it’s not a diode. To bad this forum dont have audio easier to talk then type.

For that I still suggest a longevity test, remove V1,V2,V3, hook direct video to point B as before, heck, hook audio input to pin 3 of the still connected volume control plug connector to R1 if ya want, you should get some sound, run video for 30 min ( do NOT leave it unwatched ).
If OK, try another 30, try longer, and so on.

Ok but what am I accomplishing I already have good video at test point B and my goal is to have it work with its own tuner I know you said I could take the other route with video inputs but I would rather find this headache and be done with it. After seeing the video flicker in and out clear there is another obvious problem something is more then likely leaking to ground I feel it don’t know why but I do. And an arc somewhere can only do what it did in an instant I don’t think it’s a tube. I had an rca don’t remember what chassis but I had a disc cap short dead to ground and took out the flyback and ho transistor so those caps do go bad. In this case I just don’t know.

What I did try was disconnected both diodes and ran the heaters and checked the positive side of the power supply caps and I got a very low voltage reading on the 250v 260uf string and also the 450v 80uf but all the other caps were zero so I pulled each tube one by one thinking heater cathode short but still had that small reading. These caps do go to ground but still why only these caps.

The point is to eliminate any possible problems from the video det forward first, then work back.
If you can determine that you can run the set for extended periods of time with A/V input without any strange things popping up, then you can turn attention on IF/ tuner.

But if things still act strange with A/V input when run for long periods, address that first.

Well the sound does fade on and off but that’s probably because of the lousy video

"disconnected both diodes "

but c151 was still there, right?
that gave some charge to C1, not much.

C1 & C2A = voltage doubler when added with the diodes, the other caps are filters.

C151and c152 are disc caps and both diodes completely disconnected there wouldn’t be anything flowing out of those caps from the heater string.

and about that, things of this era just do not compare to the SS one, as everything went solid state, it also went cheap cheap CHEAP, the components were just not built to the same standards, not expected to last, all disposable, hell, only a fraction of the CRTs from SS TVs even still worked after 10 years, let alone 30+!

All I know is there is something that I would call an arc because of how the hv changed and IF voltages in an instant and if the chassis was in at that moment the video probably would have been clear for that moment.

All I could do now is look at the old caps that are still in the chassis more so the ones that tie to ground along with all the rest of course they are old and should go and if there’s a bad one I will know it.

any leakage from heaters should have been AC, If it was DC, then it was most likely residual voltage from before.

Prob nothing.

I did get an ohms reading but I didn’t write it down.

Well how about this scenario being the hv jumped up and the voltages went up on the 2 IF I could possibly have a cap at the horizontal oscillator that may be defective and that would possibly change the frequency and there for mess up the agc and down to the IF strip. I never had a new bad or defective cap but I guess it’s possible.

I’m wondering why if v6 is pulled then there is no horizontal oscillator v12 it don’t run shouldn’t the oscillator run without v6. Maybe this is my problem if the oscillator should run by itself. I’m not sure looking at the block diagram if v6 is needed or not for the oscillator to run.

I'm rather unfamiliar with the way Zenith did their horizontal oscillator circuits, it's clear that this set has a clone of the Zenith and not RCA, or some other kind.

Very close to this.
https://www.earlytelevision.org/pdf/...sams_757-4.pdf

do remember , the horizontal oscillator is a phase locked loop, and where I'm not sure of all the aspects of how it's implemented in this set, but, removing V6 is most likely breaking the feedback chain, and the oscillator won't start w/o it.

Is there a reason why L42 gets really hot along with the focus coil L42 measures 35ohm so far it’s still good but why both really hot these 2 tie into the agc and noise gate kind of odd being the problems in the agc circuit. When I first got this set the 100k resistor on the focus coil was burned.

The horizontal running off frequency shouldn't effect AGC a noticable amount. If you have ever misadjusted the horizontal hold on a working set you'd see that the video amplitude stays very close to normal with the hold out of locking range....If the set by design lost IF signal because misadjusted hold screwed up AGC then the sets wouldn't be able to receive a signal unless the horizontal miraculously synced up to a station without signal....No maker would sell something so Mickey mouse.

Again, the whole point of applying the 0-9v sweep to the AGC test point was in hope that the circuit may have been malfunctioning, and by giving it external control power, it would have given the IF a chance to pass something through, but this did not help, again pointing at an alignment problem, and not related to any other areas.

EDIT==

EM addressed the resistor issue before...
"I think I have heard that if the coil is at it's extremes it will burn that 100K resistor."

But I have been looking for a draw down in voltage as a possible reason video is screwed up and this maybe it I don’t know but the focus coil and L42 get really hot L42 got so hot that the glue holding the coil in let loose and the coil fell out so I put hot glue and I just noticed the coil fell out again heating the hot glue. The resistance check on v6 and v12 were good so the focus coil and L42 both are tied to 2 locations in the agc feedback circuit the 2.2pf and the 470 pf disc caps c96 130pf is new so if the focus coil is bad or any one of the 2 caps along that line are bad then maybe this could solve it. Amazing but I found a new focus coil.

Any issues that may, or may not be with the focus coil area are not related to the tuning / IF or AGC issue, if it was, you would have seen a substantial change in video on screen when AGC test point A was given a bias sweep from 0 to 9v.

This means that no matter how AGC tries to set gain, no matter what the voltages are on V1 & V2, or the tuner, no video is going to get from the tuner to the detector diode w/o getting corrupted.
The alignment is wrong.

There are voltages between the 2.2 cap if this cap is bad then it would upset the sync sep and as been stated before is that if the sync sep is not right I won’t get video or be able to tune anything in. The voltage on pin 6 IIRC was low and should be 145v and the agc does nothing as it should change voltage via the agc pot. It’s just my thought I could be wrong.

I know I’m being stubborn but if the alignment was so far out then I would not have had the picture flicker in clear as can be for a second and I have 2 components getting very hot for a reason and need to find out why like the diode getting hot heat equals voltage so I need to find out why and if it corrects any other problems then that’s a plus.

What you may see in the first second or two is not relevant, as how any given receiver behaves before all the components come up to normal temperature and operating voltages is very different from up in a stable state.
Thus the alignment instructions clearly state “allow a 20 minute warm up period.”
What you are most likely seeing is the IF/and or tuner passing video before things have fully come up to power and stabilized, this is not unusual, the alignment method of course would be to get it to pass video when it's fully up and warm.

Also, the sync sep has been shown to be in a good state already, if it was not, you would have no video lock, and or unstable video with the direct video input.

Ok true but I still have the focus coil and the peaking coil very hot this is not right for only a minute on the focus coil could be shorted but I didn’t check it yet.

Pardon my ignorance, but what is the "focus coil" on the schematic? This set uses electrostatic focus.
Ah, nevermind - L49 - focus coil.

I still have pin 8 of v1 that the chart says 3.2k but I’m still getting 6.2k after changing the resistors so that’s a problem unless the chart has a typo. I have a Motorola book for different chassis and there is a 907-B I don’t know if mine is a B but if I take the 8.2 off ground then pin 8 shows the correct resistance maybe the 907-B is updated it’s from 1969.

I have to look into the video detect diode the one I put in may not have been good so can I mount this diode on the outside run 2 small wires to an opening on the chassis and mount it to a small tie strip for easy access to try different diodes. Maybe this diode has excessive leakage and it’s tough to reach it every time.

Altering the detector like that may result in unwanted undesired results.

How does one know if the diode has excessive leakage. Like many other things that test good but really is bad like tube testers.

The diode test with any DVM is good enough in this situation to detect any faulty diodes.
The detector is not under any high power load or voltage extremes.

Well it does check good but at this point I’ll check anything to rule out.

Still didn’t come up with the reason why pin 8 v1 is at around 6.3k when it’s supposed to be 3.2k. I’m letting everything else go for now and have to focus on this discrepancy with pin 8 v1. I don’t even know if sams is wrong because pin 8 v2 is 6.4k and matches sams.

More likely than not, the data on the SAMs is in error, and 6.3k is correct.
You should really look into what Squirrel Boy mentioned, and try injecting IF signals into the string at the various stages via the grids of the tubes, (pin 2), using a decoupling capacitor to protect the tuner subber from any voltage that may be on the grid.

Since you can't place the chassis in service position for this, or have a tube test socket, you will have to get something like some 30 Gauge Wire Wrap Wire, and wrap a few turns around P2 of the tube of the stage under test, as this has to be done with it hooked up fully to the CRT to see if you get a picture.

+1 basically your using your tuner subber like a B&K analyst's IF output....Only I'm not sure why you bought the subber instead of an analyst in the first place....I never use my tuner subber, but I use my analyst more than my scope (it's probably second to my DMM interms of use).

So your saying inject signals from the subber to pin 2 of the first 2 IF tubes. Ok well that’s next. .01 cap or .1 I’ll leave the rf plug from the tuner out while trying each tube.

Ok v1 same v2 was impressive v3 nothing so either L4 was turned or something right there at v1 is the problem or just befor it I don’t know. The picture is from v2.

This is a 1st IF problem, something between L3 and L4.

First replace
R36,R37,R38,R42,R43,R44,R45 with all new carbon film parts, do not rely on any meter to tell you the old parts are OK, at this point, you want all new resistors in there, of coarse, paying close attention to lead dress and placement when put in, making it look as close to original as you can, then go on from there.

This obviously means all is good from the 2nd IF onward, including the detector diode! :banana::D

Well this somewhat proves it don’t need a full blown alignment.

there is a problem in the first half.