Motorola ts907 low hv

[Yamamaya42]

Originally Posted by timmy

R45 on the schematic shows it’s a 560 ohm but when I measure it it gives me .551k but I know sometimes any resistor that is over 500 ohms it shows me it in k ohms same thing with the other 560 resistor. This one is green blue brown.

good site for this is..
https://www.allaboutcircuits.com/too...de-calculator/

but it does not give down to 20% you have to work that out for yourself

[timmy]

An alignment issue can keep the first 2 tubes from conducting the proper way or can they conduct and show correct voltages when an alignment is needed.

[timmy]

So I am going to pull the first tube and check the voltages on the second and if the voltages are good on the second then that narrows down to the first tube having a problem if not then first one back and I pull the second and check voltages again hopefully I can get it down to one tube I can’t believe that both tubes developed a problem at the same time.

[Yamamaya42]

Originally Posted by timmy

An alignment issue can keep the first 2 tubes from conducting the proper way or can they conduct and show correct voltages when an alignment is needed.

It does make some sense that if the alignment was off, that the tube dynamics would be upset to some degree, but how much, who can say.

[timmy]

First tube pulled 7- 252 8- 136 3-5 2-4
Second pulled with first put back in 7-242 8-130 3-7 2-15v

[Yamamaya42]

It's almost as if the alignment is WAY off, and AGC is trying to compensate for it by messing with the gain of stages 1-2.

the numbers gave today are relatively normal, compared to the ones yesterday, namely voltage on pin 8, (130ish ) where it was 60v ish last time you tested.

This is probably being caused by.
AGC changing gain of these tubes.
Changes in voltage on the 275v line.
Changes in value of the 3w/2w power resistors on pin 8 as they heat up.
This added with the fact that the alignment is most likely off to start with.

[timmy]

Don’t voltages normally go up when a tube is pulled? And I checked voltages also with no antenna and no change.

[Yamamaya42]

Originally Posted by timmy

Don’t voltages normally go up when a tube is pulled? And I checked voltages also with no antenna and no change.

the draw of an IF tube is so small, it won't matter that much, in or out.

[timmy]

Well I don’t understand how a 100v drops to 60v that’s not so small of a draw I would think

[Yamamaya42]

Due to the action of the AGC, the 1st and 2nd IF is in constant flux, using horizontal pulses and video as reference points, even with garbage video, AGC will try to gain on those tubes via cathode and grid 1, this of course will have an effect on the other tube elements when this takes place.

Where it's hard to be sure why that 100v on pin 8 dropped liked that, it's unlikely that it was because that 275v was low, so it's prob tube biasing and / or related to the age of the resistors in the area coupled with the fact that alignment may be off.

Alignment is all but impossible to correct given the current situation, but upgrading to better resistors is a pain, but rather cheap.

[timmy]

I can’t help but go back to having sound stronger on channel 4 then 3 but the one day I had the set on and the sound just faded into distortion and static but can still make out voices and that’s how it still is so if alignment was the cause sound would not have been good in the beginning so I still believe the loss of sound has got to be the reason for bad voltages and no video.

[timmy]

So if you think the agc is trying to clean up a bad signal then what if I pull the 6hs8 agc tube then see if voltages get better on the first and second IF tubes.

[timmy]

Well pulled the agc tube didn’t make a difference.

[Yamamaya42]

Read page 8 of the sams, where is says “alignment instructions” , the better choice is to do as it says, connect a variable voltage to point A, and adjust to what ever needed, 3v 4v 2v, this overrides the AGC control, for alignment, this can sometimes be done for testing.

[timmy]

I think I’m going to try and get the 12 caps across the IF strip and change them. there are some that are shiny almost to say they got hot or whatever the reason is they get the oil or wet look. Something took out the sound that I had. maybe I’ll get lucky and find one that is leaking or partially shorted. I checked voltages this time with no antenna and pin 8 on both tubes still low.