Motorola ts907 low hv

[timmy]

So is it safe to say that even though injected video is stable and locked that there could still be a problem in the sync sep section knocking out the video path from the IF.

[Yamamaya42]

The 6HS8 is a dual function tube, even though the two sections share cathodes & G 1 and 2, the sections work independently, the sync sep section being on the right, AGC on the left, it is the video on pin 9 that is used for sync sep, and pulses on pins 3&6 for AGC.

[timmy]

I’m going to try that idea with the 9 volt battery and the pot what pin on v6 or where was the agc tap

[timmy]

So page 6 says to hook it up and see if it is over loaded so how is this supposed to work more 9v would clear it if it were over loaded I know it changes bias because it looks like it’s already overloaded I just need to completely rule this out for sure.

[Yamamaya42]

Originally Posted by timmy

So page 6 says to hook it up and see if it is over loaded so how is this supposed to work more 9v would clear it if it were over loaded I know it changes bias because it looks like it’s already overloaded I just need to completely rule this out for sure.

overloaded would be evident by a clipped wave or too high signal shown on the oscilloscope, but since you are going by what you see on the screen, things will be a bit different.

[Yamamaya42]

This may help to understand it a bit better, in this he drastically changes the AGC gain via external bias to a state over and under saturation,

https://www.youtube.com/watch?v=I1h5zNFvn_U

[Username1]

Good Morning:

If you really wanna see if your AGC is working, you could build a single transistor amplifier
4 resistors, total 47K on the outputs, 450K on the inputs, 18V supply, give you a
nice 5V P-P signal swing and feed a signal to it, and put it on your video in test point.
Without a scope you would have to go by what is on the screen. You got other tv's
so pick one put a signal on it and turn the AGC through it's range and watch the
screen......

Something like this:

https://www.electronics-tutorials.ws...ier/amp_2.html

You have to try and reach your required 5V P-P signal, so give it a try, you might
even have to use 2 transistors if you need to flip the signal, so keep that in mind....

I'm sure Yamamma can help out with it he seems to be able to find all kinds of goodies
online.

Once you get a proper signal your sync sep & AGC should work as expected....
With all the stuff & Time you spent up till now I think this may be a good step
to take..... Just keep in mind you will only see some voltages change, not
necessarily see a difference in picture etc. because AGC will not have an effect
on the picture because the signal is fed late in the system......

Poor signal would look washed out & poor H & V Lock. Overloaded pic would be very
high contrast, & noise on white lettering, possible H or V Lock on dark parts of the
picture resulting in a tearing look. I'm sure there are example pictures online....


.

[timmy]

I don’t know one minute it looks like it’s overloaded and then it looks like a weak signal.

[timmy]

I checked the voltages on v1 and 2 and they are spot on with the sets tuner being used and I seem to get more on screen using the tuner then the subber I really would think I would get more with the subber being it has a gain control. I don’t know what the difference is between the subber plug and the tuner plug really nothing yet the tuner has more activity.

[Username1]

Well, regardless of what tag they put on that subber, I would imagine that any adjustment
is to boost, or decrease output so as to change the level of signal available to the IF
section, not really the same thing as gain.....

Well, If you get something through the system directly from the TV's own tuner, that
is a major improvement, and big steps forward! And if that's the case, you should
definitely forget about feeding anything to the video test point, and work on the
battery AGC test point, and possibly even think about weather or not it's worth
the gamble of turning the trap coils to see if you can get more signal through.
But remember what was in that IF alignment video from this morning, you
have to remember each coil is peaked for a different frequency in the
full bandwidth that needs to make it through that section.... So
peaking one wrong will cause more problems....

Also if you are really getting a overloaded picture one minute, and a weak looking
picture the next, then you need to figure that one out.... Possible intermittent....
You may need to figure out how to clean the tube sockets & tube pins in a
really effective way..... Seems like you are getting closer to fixing this
one! And to do it before this thread hits 100 pages would also be
way-cool!!


.

[Electronic M]

Originally Posted by Username1

Well, regardless of what tag they put on that subber, I would imagine that any adjustment
is to boost, or decrease output so as to change the level of signal available to the IF
section, not really the same thing as gain.....

Well, If you get something through the system directly from the TV's own tuner, that
is a major improvement, and big steps forward! And if that's the case, you should
definitely forget about feeding anything to the video test point, and work on the
battery AGC test point, and possibly even think about weather or not it's worth
the gamble of turning the trap coils to see if you can get more signal through.
But remember what was in that IF alignment video from this morning, you
have to remember each coil is peaked for a different frequency in the
full bandwidth that needs to make it through that section.... So
peaking one wrong will cause more problems....

Also if you are really getting a overloaded picture one minute, and a weak looking
picture the next, then you need to figure that one out.... Possible intermittent....
You may need to figure out how to clean the tube sockets & tube pins in a
really effective way..... Seems like you are getting closer to fixing this
one! And to do it before this thread hits 100 pages would also be
way-cool!!


.

At page 75 he needed to send Yamamaya42, you and a half-dozzen other people a gold watch for the time invested in this shit-show.

[timmy]

With the set using it’s own tuner there is a picture but it’s got no contrast and I’m able to adjust the horizontal so there is no lines and it’s a steady picture but it flickers in and out if I just touch the channel knob it will go out and I touch the knob and can get it back but there’s a lot of white because of no contrast so maybe there’s something going on with the tuner almost as if the tuner tubes are no good. And the battery bias test didn’t change anything that I was able to see.

[Username1]

If the tuner knob causes the picture to go in & out, then you need to focus on getting
good solid connections on each channel. Take the tuner apart, cover off, & use a wood
stick to poke around till you find the most sensitive parts and try and figure out
what is not making good contact. Don't worry so much about voltage checks
or replacing parts. Go after making the tuner solid when on a channel.

In our shop we use to clean all contacts with a gritty cleaner on Q tips,
probably not available any more, today I think the closest thing would
be the mildest valve grinding compound. You could use silver polish
or Ajax, something with really mild abrasive. But we had to remove
all of that stuff after it's use, so whatever you use be sure to use
small amounts, keep it confined, use Q tips, and remove it all.
Then after be sure to spray it with Tuner Cleaner so you
protect it from oxidation......

Be sure the switches are in good shape before moving on to see if it's a
loose component, ground, or tube socket. Clean tube sockets too.....





.

[timmy]

I would have to take the tuner out to reach all that I would have to clean and at the same time check resistors in there I think there are 7 resistors.

[Yamamaya42]

It's not recommended to do anything with the caps / resistors in the tuner, because to disturb them can cause more harm than good, even if they are out of tol.

What could be done is removal of the drum to allow better cleaning, but this is not easy to do as the spring clips holding it in on each end are a pain to get in and out, and very close attention to detail to all the parts on both ends of the shafts must be taken so that they go back in place.
But, once the drum is out, you have easy access to the spring contacts inside for cleaning and tightening if needed.