Motorola ts907 low hv

[jr_tech]

Originally Posted by timmy

It’s permanent and when it was at 35 ohms it started getting hot and went up from there.

In the past, did you ACTUALLY measure the coil to be 35 ohms, or are you relying on the SAMS measurement for your baseline “before” number?

jr

[timmy]

When it first started getting hot I measured it and it was 35 ohms.

[Yamamaya42]

Originally Posted by Username1

If you are so worried about the L42 Temp. then just put a 10 Ohm 10W resistor in
series with it, and check it's temp. and move on till you get a pic on the screen
and then you can figure it out.... I mean like a Good Pic from the tuner
with everything else working.....




This should be your main focus:

Every TV without a signal should produce snow on Picture & Sound
this one does not. You tracked the signal loss to a specific area, & now
need to focus on why it's getting lost. IF Amp not working? IF amp
turned off because of some AGC Fault?



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I agree with adding this resistor, you should also stick on the ceramic heat sink using thermal conductive epoxy as I mentioned, save the coil as best as you can.

[timmy]

Originally Posted by Yamamaya42

I agree with adding this resistor, you should also stick on the ceramic heat sink using thermal conductive epoxy as I mentioned, save the coil as best as you can.

With injecting video point b would the agc affect that video since it follows to the video amp.

[timmy]

I do remember when agc is maxed it has a blank screen like I have now so if that’s the case then I have to find out if it’s maxed with the pot at minimum. There one wire that goes to v1 from the v6 area maybe I should disconnect it and see what happens at this point.

[timmy]

Ok so I have a theory the high voltage across L42 my theory is that the voltage on the path of the 470pf cap which goes to v6 as well as the 2.2 cap coming off the agc pot both those voltages come from the flyback so if infact there is still a problem with v6 then I think it’s safe to say the tube is not conducting correctly if any at all because if it were conducting then I think it would relieve excessive voltage at L42 because right now it appears to be solid standing voltage on both sides of L42 780v. That may explain why removing one lead from each cap having no change and still heating L42. Which in turn possibly shutting down v1 having no snow on screen and no video.

[Yamamaya42]

Originally Posted by timmy

Ok so I have a theory the high voltage across L42 my theory is that the voltage on the path of the 470pf cap which goes to v6 as well as the 2.2 cap coming off the agc pot both those voltages come from the flyback so if infact there is still a problem with v6 then I think it’s safe to say the tube is not conducting correctly if any at all because if it were conducting then I think it would relieve excessive voltage at L42 because right now it appears to be solid standing voltage on both sides of L42 780v. That may explain why removing one lead from each cap having no change and still heating L42. Which in turn possibly shutting down v1 having no snow on screen and no video.

That is not how it works.
The AGC circuit does not take any voltage away from there via C59, it does take filtered horizontal pulses from the FBT, any DC is blocked by C59.

That lower winding on the FBT serves more than one function, one of them is generating +/- 500v AC horizontal pulses AND the boost voltages, pin 9 being the pin where power is fed in.

ALL PINS are at DC boost potential in the focus circuit, this is normal.
As there is no diode used in this boost setup, no matter where you measure, you will see boost level voltage in this area.

So there is no “excessive voltage on both sides of L42” the entire area is at 780v DC and this is normal.

What is causing it to heat is the AC pulses it's getting and nothing with any DC voltage in the circuit.

[Yamamaya42]

Originally Posted by timmy

With injecting video point b would the agc affect that video since it follows to the video amp.

Yes and no.

If the video fed in was up to the level needed at that point, 5v ptp, it would start to fool the AGC into thinking that there is good video coming in and start to do it's thing, but since it is low at 1v, it is still like a weak/ no signal from the tuner.

[timmy]

Originally Posted by Yamamaya42

That is not how it works.
The AGC circuit does not take any voltage away from there via C59, it does take filtered horizontal pulses from the FBT, any DC is blocked by C59.

That lower winding on the FBT serves more than one function, one of them is generating +/- 500v AC horizontal pulses AND the boost voltages, pin 9 being the pin where power is fed in.

ALL PINS are at DC boost potential in the focus circuit, this is normal.
As there is no diode used in this boost setup, no matter where you measure, you will see boost level voltage in this area.

So there is no “excessive voltage on both sides of L42” the entire area is at 780v DC and this is normal.

What is causing it to heat is the AC pulses it's getting and nothing with any DC voltage in the circuit.

Well here is another theory is it possible that being there is no video for the focus to work that is the possible reason why it’s getting hot. The focus coil gets hot also. So just because the resistance check on v6 was good don’t mean there is no problem there.

[timmy]

If the agc was at max what at v6 could create this with the pot at minimum

[Yamamaya42]

Its still suggested to do as SB said, get a 10 or 20 ohm resistor, stick it in series with L42.
https://www.amazon.com/HONJIE-Power-...7771596&sr=8-1

Get IF working.

add a small ceramic heat sink 15mm.

[timmy]

Ok I got an 18 ohm 10 watt resistor so if I put this in and the catch is if this focus L42 issue has anything to do with v1 and not having video then I’ll be waisting even move time looking for something I may never find.

[Username1]

Just some evening AMC Rambler-ings,,,, If you want to see if the AGC is doing something
you might want to feed that tuner subber back to V2 where you had a pretty good
picture, and make some before & After voltage measurements on the AGC line.
You might also want to play around with the AGC control while there is a nice
picture on the screen, and see if there is a voltage change on the AGC line,
it's not so important to see a change on the screen at this point.

As for L42, you can do one of 2 things... Cut it out and throw it into the pond, or
you can try to protect it as best you can. Coils are made of 2 things, An Ideal
inductor, and some resistance - from the copper. If this coil really really did
change it's resistance, and increase, then it's already burned. If it's getting
Hot, it's because Current is heating up the resistive part of the coil.
So the current is either coming from a AC, or Pulsed DC signal
causing a field change in the coil sufficient to cause large
enough current to make it hot! The other possibility
is there is large current flowing through it and
making it hot...... That's really the only
2 possibilities...... Unless, it's within
distance to be inductively coupled
to another coil causing current
to flow in the coil...... So, is
this tv too close to your
Warp Coils ?


.

[timmy]

This L42 is just a roll of very fine wire no ferret on it just wire.

[Username1]

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I'm wondering about the path of current through L42, I think the thinking that C96
could have been shorted to send high voltage & a current path through L42 is not
correct. But the regular current path of from Pin 5 to Pin 1. Since the flyback
windings are low ohms, that's a lower voltage, & high current source.
Much higher current than the HV winding... Transformer Basics....

How is that 10 Ohm resistor R136, I know you probably
checked it 4 times already....

So do you have control of the HV adjust?
Does it work?



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