Motorola ts907 low hv

[timmy]

I’m trying to figure out what’s going on with this Motorola I’m obviously missing something here bright up 14kv bright down 20 kv with little to no difference by turning the hv pot. B+ is 375 and sams says 385 I tried cap off reg tube no difference all caps at the oscillator changed and no smell of leaking hv. I have a new flyback but don’t want to change it until I go over everything that I may be missing. Another oscillator tube nothing makes a difference. If anyone has even a clue I’m all ears. I don’t have a scope which would probably help I also checked the ohms of the horizontal hold coil which sets the frequency and the hold and ohms are good.

[nasadowsk]

Off frequency? Bad voltages to Output tube? Are you getting a picture that locks?

[Yamamaya42]

what CRT is in the Motorola ts907?

there is very little info out there on this set out there.

Also, why start a 2nd thread? you already have a topic about this set under the fried focus resistor.

Would it not all be easier to follow if it were all centralized under the same one?

[timmy]

Originally Posted by nasadowsk

Off frequency? Bad voltages to Output tube? Are you getting a picture that locks?

Sound but no picture full screen missing edges both sides due to low hv

[timmy]

Originally Posted by Yamamaya42

what CRT is in the Motorola ts907?

there is very little info out there on this set out there.

Also, why start a 2nd thread? you already have a topic about this set under the fried focus resistor.

Would it not all be easier to follow if it were all centralized under the same one?

This set has the 21fjp22 and I started another thread because the focus coil resistor I don’t think has anything to do with this hv issue

[Yamamaya42]

Originally Posted by timmy

This set has the 21fjp22 and I started another thread because the focus coil resistor I don’t think has anything to do with this hv issue

they could very well be related to each other, as they are both in the same section, and tied closely together to the function of the HOT & FBT.

[timmy]

Had a weird they happen twice I was disconnecting everything to take the chassis out and touching plugs to unplug with one hand and my arm was lightly setting on the hv cage and I was getting lightly zapped from the voltage in the crt now that would be impossible but until I removed the anode wire from the crt I was good to go. This makes no sense because the anode is in the hv cup with the 3at2 tube so how can this voltage make it to ground I have no clue. And there is a ground for the crt and that was good.

[Yamamaya42]

Remember, the crazy thing is all one big tuned circuit!

From one end to the other, it's amazing how they got it all working so well, but, it DOES mean it's easy to upset the balance, get one key element out of wack, be it the horizontal frequency, something in the damper area, yoke or convergence area, basically ANYTHING that can mess up resonant frequency of the circuit, then you have a big headache on your hands, and like I mentioned, it may very well include the focus circuit.

[timmy]

On a bk tube tester and recapped I tested the hv rectifier and it’s new but on the scale it tested on the end of the yellow bar which is around 62 on the scale I would think it’s no good but I don’t know how low it has to test befor seeing a hv problem so I tested the old one the tv came with and reads almost 90 on the scale. I didn’t try it yet but how low can this tube test befor it’s a problem.

[Yamamaya42]

Originally Posted by timmy

On a bk tube tester and recapped I tested the hv rectifier and it’s new but on the scale it tested on the end of the yellow bar which is around 62 on the scale I would think it’s no good but I don’t know how low it has to test befor seeing a hv problem so I tested the old one the tv came with and reads almost 90 on the scale. I didn’t try it yet but how low can this tube test befor it’s a problem.

Unfortunately, as is often the case with tube testers, especially with the power type tubes, they never give the full story about good/bad because they can't put them in real life load situations that they would be in the circuits they are being used in, in these cases, it's always best to try a "known good" one.

cause they often fool you.

[Yamamaya42]

WAY TOO MUCH info on tube testers, but it shows what you gotta deal with.

http://www.tungsol.com/html/faqs7.html

[timmy]

I don’t know if these series chassis were known back in the day for flyback failures the last Motorola I had I changed the flyback so with this one I have a new flyback and I put it in so I’ll see what happens. I keep going over this chassis and every cap I changed tested new and every resistor I checked tests new as well so if I still have low hv then maybe the yoke. I’m not sure really how to check the yoke coils ohms. I changed the rectifier tube and gained 4 kv but just won’t adjust via the hv pot it will lower from where it is but that’s it.

[timmy]

Boost voltage off the flyback is around 750 volts should be 770 volts after a 10k resistor and b+ is 350volts and should be 385 volts. I don’t know if the b+ diodes go weak from age has anyone had these diodes go weak by not putting out the correct voltage and if b+ is low everything else will be low. And the line voltage is 111 volts. Originally the b+ was 375 volts I don’t know why it dropped.

[nasadowsk]

If the boost diodes are selenium (possible) I’d be looking there.

[timmy]

B+ diodes no boost diodes in this set.