Motorola ts907 low hv

[Yamamaya42]

that is NPO then!

[timmy]

Ok short history of this set with me, I got it changed the power supply caps didn’t change any other caps put the chassis in tried it , it had low hv and no video so what I have done to date didn’t affect its operation in a positive way except for the hv. I really expected it to work as all of my other sets in worse condition then this one. And I put the 18 ohm 10 watt resistor in series with L42 still getting hot. And it does appear that on dc scale I’m getting 7.5 vdc on the tube side of the 470pf if it was ac my meter jumps back and forth to indicate it’s on wrong setting.

[timmy]

That cap had ac on it with leg off the 7.5 vdc is on the tube side with leg off

[Yamamaya42]

The 7.5 vdc on pin 3 of V6 (far side C59) is perfectly understandable, as there is no video for the circuit to compare to and thus no pulses on pin 6, the gain is being turned up to the max, if you were to hook up the subber to the grid of V2 like you did before, as Squirrel boy mentioned, using a decent video source, and adjusting R14, you should see that 7.5 vdc come down as the AGC tries to bring down the gain.

[timmy]

So now I’m checking L1 L2 L3 so far they are looking ok. I do remember having the video put tag pin 2 of v2 getting video I turned the agc made no difference in the Video I got. I did check the agc it does vary not much.

[timmy]

R23 is a trap but it has no wiper it’s attached at each end and would usually have a center for the wiper it has the adjustment knob but no wiper

[Yamamaya42]

Not with it the way it is working now, you won't see it change much.
But as suggested, if you feed the tuner subber into pin 2 of V2 as you did the other week, giving it a good source like DVD something else with good sync, the AGC should respond much better.

You won't see any change on the screen, BUT, the voltage at pin 3 of V2 should change as you adjust R14, the same changes should be seen at pin 3 of the tuner plug.

[timmy]

Originally Posted by Yamamaya42

Not with it the way it is working now, you won't see it change much.
But as suggested, if you feed the tuner subber into pin 2 of V2 as you did the other week, giving it a good source like DVD something else with good sync, the AGC should respond much better.

You won't see any change on the screen, BUT, the voltage at pin 3 of V2 should change as you adjust R14, the same changes should be seen at pin 3 of the tuner plug.

Well I already seen the voltage does change at max it’s only 135v. All 3 coils test good the only other is the 8.2pf cap at antenna input.

[Yamamaya42]

Originally Posted by timmy

R23 is a trap but it has no wiper it’s attached at each end and would usually have a center for the wiper it has the adjustment knob but no wiper

picture please...

if R23 is broken that is a BIG PROBLEM, and 99.9% likely you can't tune in anything.

the traps are de-tuned and nothing can get to the 1st IF to get processed.

[timmy]

Are you saying that they are pre-tuned I didn’t touch the blue knob.

[timmy]

It say it’s 15k but can’t measure it because the .2 that the coil is showing across the trap will show before the 15k. So how are they checked why would it have gone bad if it did.

[Yamamaya42]

Originally Posted by timmy

It say it’s 15k but can’t measure it because the .2 that the coil is showing across the trap will show before the 15k. So how are they checked why would it have gone bad if it did.

Those types have brass communicators hidden under the plastic disc, they make contact with little carbon traces that are formed into the ceramic resistor base below it.

It looks fine, don't turn it cause it will make things worse.

[timmy]

Originally Posted by Yamamaya42

Those types have brass communicators hidden under the plastic disc, they make contact with little carbon traces that are formed into the ceramic resistor base below it.

It looks fine, don't turn it cause it will make things worse.

It’s not broke in anyway if it was turned it can be put back where it was correct.

[Yamamaya42]

https://www.robotroom.com/Trimpots-2.html

not exactly the same, but you get the idea!

[timmy]

Well now to figure out the next step.