Motorola ts907 low hv

[Yamamaya42]

This would be correct if the circuit were working as intended, but it may also so out of wack that it won't let you tune in anything.

The intent of doing this bias sweep on point A is to see if it has any effect at all on the screen, better / worse.
If there is a noted change, then it prob is AGC related, if not, then it's IF and alignment.

[timmy]

I’m going to go over a few resistors in the agc circuit then on to the 9v get up.

[timmy]

Just for the heck of it chassis back on back but upon plugging it in have a test lead on v1 with antenna and just as the hv came up it jumped 4kv and when it did the voltages on v1 and 2 neared 100 v then hv dropped again did this twice this just about confirms something is getting in or shorting intermittently somewhere. I never seen this since working on this chassis.

[Yamamaya42]

Originally Posted by timmy

Just for the heck of it chassis back on back but upon plugging it in have a test lead on v1 with antenna and just as the hv came up it jumped 4kv and when it did the voltages on v1 and 2 neared 100 v then hv dropped again did this twice this just about confirms something is getting in or shorting intermittently somewhere. I never seen this since working on this chassis.

The voltages when it first comes on really don't mean that much, it's once it is all warmed up and stable that matters.

There is a reason for doing the AGC bias test, this goes back to 2016 when I was working on my CTC-16XL and it too had IF problems, and old_tv_nut said the following..
---
The AGC circuit is a feedback circuit. This means that the 9 volts at the plate does not necessarily mean anything is wrong with the AGC circuit itself. It may be getting an incorrect detected video signal at the grid due to some other reason (like a dead IF) and trying to correct it by changing the AGC voltage. You need to check the detected video for starters. If it's missing, check and/or replace the AGC tube. And, you may be right that some component is bad. Check all the voltages in this area. Check resistor values wherever voltages are way off. Further trouble shooting could involve breaking the feedback loop by connecting an adjustable bias to the AGC line, as you would for aligning the IF. If video is missing or wrong amplitude and you can't get it by manually setting AGC bias, there is something dead in the IF or tuner.
---
so please try that bias override, and see the results.

[timmy]

Originally Posted by Yamamaya42

The voltages when it first comes on really don't mean that much, it's once it is all warmed up and stable that matters.

There is a reason for doing the AGC bias test, this goes back to 2016 when I was working on my CTC-16XL and it too had IF problems, and old_tv_nut said the following..
---
The AGC circuit is a feedback circuit. This means that the 9 volts at the plate does not necessarily mean anything is wrong with the AGC circuit itself. It may be getting an incorrect detected video signal at the grid due to some other reason (like a dead IF) and trying to correct it by changing the AGC voltage. You need to check the detected video for starters. If it's missing, check and/or replace the AGC tube. And, you may be right that some component is bad. Check all the voltages in this area. Check resistor values wherever voltages are way off. Further trouble shooting could involve breaking the feedback loop by connecting an adjustable bias to the AGC line, as you would for aligning the IF. If video is missing or wrong amplitude and you can't get it by manually setting AGC bias, there is something dead in the IF or tuner.
---
so please try that bias override, and see the results.

So I assume the voltages at the agc tube 6sh8
3 7.95v 9 32.53 6 116 7 83. Doing the 9v setup then check voltages?

[timmy]

Well it’s official the 9v setup proves an agc problem voltage jumps up 11 volts on v1 and that’s a huge difference using the only pot which was 900k

[Yamamaya42]

This should be done with the crt hooked up and a signal being fed in the tuner, adjusting the AGC bias to see if it makes any marked improvement in the picture on screen.

[timmy]

Originally Posted by Yamamaya42

This should be done with the crt hooked up and a signal being fed in the tuner, adjusting the AGC bias to see if it makes any marked improvement in the picture on screen.

Ok let’s say it makes a huge difference nice picture what would be the next step because I’m lost at this point I have checked all the resistors in and around the tubes associated with the agc so if this proves to give a great clear picture what’s next.

[Yamamaya42]

If it does turn out to be an AGC related issue, the whole AGC / NOISE GATE system will have to be taken into account, as Old TV Nut pointed out, this is a feedback system, involving not just the 6HS8 immediate area, the whole point of this is to find if there is or is not a problem in this circuit.

if there is not, then on to the IF.

[timmy]

Well unfortunately the bias test did nothing I even jumped the pot and gave it 9 v no change. This is beginning to really hurt. So I guess the agc is trying to fix or adjust the input.

[Yamamaya42]

Since you have given test point A a bias sweep of 0-9v with no results, and been over the resistors in the IF section more than once from what I can see, this basically only leaves one thing left, the IF is badly out of alignment, this is likely causing AGC to overcompensate, as there is no video for it to reference to, causing the abnormal voltages.

Who knows, the de-tuned state may also disrupt the normal voltages, be that as it may, color sets are quite hard to align even for the most experienced techs with the right equipment on hand.

It took me 3 tries to align my BW Arvin set (45mhz), and that was just with a frequency generator and a volt meter.
But for color, you need a sweep marker generator and a oscilloscope plus lots of know-how.

But the one thing that must never be done is, try to visually align a color set's IF, this will always end badly and make is worse than when sttarted.

[timmy]

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.

[Yamamaya42]

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.

[timmy]

Originally Posted by Yamamaya42

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.

[Yamamaya42]

Originally Posted by timmy

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.

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+!