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-   -   Motorola ts907 low hv (http://www.videokarma.org/showthread.php?t=275174)

timmy 08-27-2022 05:12 PM

I could answer all you wrote if you want my number let me know it will only take a few minutes so much typing lol. The audio trans checks perfect 80-81-82 resistors perfect and after having the set on the last time I had an antenna on channel 3 fades alittle probably out of tune but channel 4 sound was perfect but heard no snow with antenna off and yes I made a mistake pin 2 is a green wire is the wiper set on it measured 280 mv But the tube didn’t red plate until I had the chassis out and found the 150 resistor burned. The tube just seemed to get really hot fast now I find within 30 seconds the 6aw8 and the video output 6hb6 get really hot fast I have read that low b+ is not good for tubes maybe things change with the tube conducing at low voltage. My initial finding was I had no video so maybe something in the video area causing all this.

Username1 08-27-2022 06:49 PM

It is always possible you have more than one problem. If you suspect the Video Output
tube is using too much current, then you need to do voltage checks at each pin & see
if you find any burnt looking parts in that circuit. It's also sourced to the 385V.

The video amp 6AW8A is also sourced to the 385V.

But if the audio out tube accounts for all the extra power supply draw, then we may be
getting ahead of ourselves.


.

timmy 08-27-2022 06:56 PM

That’s just it there is nothing I’m finding resistors check perfect it makes no sense I thought maybe something in the convergence but I don’t think there is any high voltage points there to pull it down.

Yamamaya42 08-27-2022 07:06 PM

keep in mind, as stated before , audio output tubes always tend to run hot, as do horizontal outputs, this is just par for the coarse and does not mean there is something wrong.

timmy 08-27-2022 07:08 PM

Ok maybe so but I still have the low b+ and no video and I went over the video amp and output and found nothing I did suspect the 1n60 but I do have sound.

Username1 08-27-2022 09:22 PM

If the sound is clear, and you replaced the cathode resistor, and that circuit seems ok,
then it's time to check the next circuit. It may seem frustrating because there is no
dead short, and everything mostly works, but somewhere you may have a tube
with bad voltages on it, improper biasing, and using too much current.
It will take time to find it, Most likely with tedious voltage checks.

.

Yamamaya42 08-28-2022 12:06 AM

You still have yet to get a decent DVM that has a decent amperage range to check what current draw you really have at L54 right after the voltage doubler.

And until you can do this correctly, as you have stated that the meter you have does not have the range to do so, you are just going on assumption.

GET A decent DVM and check the current at that point to see if it is indeed excessive.

this is an important step.

timmy 08-28-2022 06:53 AM

Going to try something I have been using a 10 foot extension cord to power this tv so with the resistance of the extension cord and the thermistor and using a power cord from a b&w tv very thin and an air conditioner running from same outlet maybe this will make a difference, excessive resistance would cause this.

timmy 08-28-2022 11:30 AM

Well that didn’t work but from the first day I plugged this set in it red plated one horizontal tube and it’s still doing that now only one tube and it’s now looking like the pulling down of voltage maybe in the horizontal the oscillator runs but after warm up plug in again the oscillator will not start again until it sets for awhile and cools down. I don’t know if the yoke would affect the horizontal oscillator from starting. This happened with the old flyback but I since changed the flyback with a nos one. Problem is the voltages across the board are still low it’s not like I can look at voltages and see that one rail is lower then the rest and go to that area b+ low everything is low.

Username1 08-28-2022 02:46 PM

hummmm Red Hot Tube Plates = Too Much Current.

Is G1 for each tube -45V?

Maybe you need to take a break from this tv for a few days......


.

timmy 08-28-2022 02:52 PM

The g1 was low to begin with so I turned it down more like not even a 1/4 up. Took the chassis back out to double check the 2 timing caps .0039 and .0068 it’s always possible I reversed them especially because the print on them is so small I should have used a magnifying glass that’s how small and yes I should get away from it. But only 1 tube, hmm.

Yamamaya42 08-28-2022 03:33 PM

here is the biggest help to know when hor osc is OK.

https://i.imgur.com/afNm19c.jpg

best investment you can make.

timmy 08-28-2022 04:10 PM

I know but it wouldn’t pay for me since I would use it once then put it in the closet lol ��

zeno 08-28-2022 04:37 PM

Not sure you are checking the right " G-1". We mean the G-1
of the hoz out tubes. They are in // to give enuf output.
Typical sets draw abt 210 ma this one IIRC 240, beyond most
hoz out specs. Thats why 2 HOT's. Others did it in the early days.
Admiral did & if you changed the FBT there were pages to mod the
set to use one 6KD6 H out NOBODY wanted to do them.
If that neg voltage is not there the tubes stay on too long.
See class C amps. !
Once one fries the other takes over. That one will overheat trying
to supply the HV but one cant keep up current demands.
Bottom line is without the proper G-1 voltage you will cook up expensive sweep tubes. Fix that FIRST if needed !

enuf fer now
Zeno:smoke:

timmy 08-28-2022 04:57 PM

This from the start didn’t do this all the time was random then it was ok now it started doing it again when the oscillator is running I have perfect hv. Maybe it’s because the b+ is low creating this. Only tube I can’t test is the damper.


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