Motorola ts907 low hv - Page 18 - Videokarma.org TV - Video

timmy · #**256** 09-07-2022, 01:32 PM

Well that was short lived tried some tubes and again voltage drop with audio tubes still out.

Yamamaya42 · #**257** 09-07-2022, 01:40 PM

You should be able to cycle through all channels and see some sort of effect on the screen.
But, I do find that “sticky-gummy” condition of the tuner a little disturbing, if it IS old lube, (not sure) it may be interfering with contacts and hard to clean out unless something like deoxit is used since the RS stuff is hard to get, but It's a bit costly.
As far is I know, it should not be “sticky-gummy” in there, my Arvin TV tuner was like that, full of varnish, and it was hell cleaning it up.
I would still suggest a new set of IF/ tuner tubes however.

timmy · #**258** 09-07-2022, 01:43 PM

But the voltage pulled down again with audio tubes still out it has to be related and the contacts in the tuner very little dirt I did all the contacts no more sticky feeling wasn’t that bad at at.if a disc cap to ground is shorted is there any tell tale signs of maybe getting hot.

Yamamaya42 · #**259** 09-07-2022, 02:00 PM

This then, is still likely a horizontal oscillation / sweep issue, as was pointed out way back, it is a giant feedback loop, if everything is not just right, the loop will collapse in on itself, oscillation stops, and the 6JM6s start to destroy themselves.

Where disc caps have been known to fail, it is very rare for them to do so, when they do short, they are hard to find, you often have to hunt for them by looking for a overloaded feeder resistor.

timmy · #**260** 09-07-2022, 02:12 PM

This is crazy I went over this chassis and found no bad resistors I am at a total stop the horizontal coil the oscillator tube and resistors around that area were good and the coil tests perfect ohms 85 another flyback numerous tubes I had changed the horizontal centering pot centering does work I also unplugged the horizontal from the yoke voltage still dropped 2 sets of power supply caps. What would cause an upset in the feed back loop.can a problem in the sound feedback to upset the video

Yamamaya42 · #**261** 09-07-2022, 02:24 PM

This seems to be a very finicky set to get going, and it looks to be teetering right on the edge of working / non-working, could be any number of things, a cap or coil that is just not to it's liking, or when something gets warm/cold it starts/stops working, this seems to be one of the most dreaded of situations, an intermittent fault.

Yamamaya42 · #**262** 09-07-2022, 02:30 PM

I would try to take a step back to where you had the most success, with tuner and sound tubes unplugged, see how long set can run with video input via test point B, 10min? 20? longer?
Does it mess up at all like that?

timmy · #**263** 09-07-2022, 02:37 PM

What happens is put on cold no problem with voltage warm up then turn off then back on that’s when the voltage problem starts after it’s warm.

Yamamaya42 · #**264** 09-07-2022, 02:59 PM

There are only 3 tubes that seem to be connected direcly to power, audio output, sound det ( removed) and V6, SYNC SEP AGC/ NOISE CAN, if V6 is faulty, shorting when getting hot, this could be a problem and would not show in a tester, I have seen a AGC tube short before in a set and load power (it was a 6au6)

timmy · #**265** 09-07-2022, 03:17 PM

Well I have v6 coming it’s a 6hs8 in the mail and yes there is a lot of power arrows and that would mess up video and probably take down horizontal with all that power there. I have to wonder what killed the sound all the other times the voltage pulled down I still had sound.maybe for giggles I should put that tube on the tester to get hot and see if anything shows up maybe even put the heater up a notch. I tried it on the tester 7-8 v showing grid emission.

Yamamaya42 · #**266** 09-07-2022, 04:05 PM

Quote:

Originally Posted by timmy

Well I have v6 coming it’s a 6hs8 in the mail and yes there is a lot of power arrows and that would mess up video and probably take down horizontal with all that power there. I have to wonder what killed the sound all the other times the voltage pulled down I still had sound.maybe for giggles I should put that tube on the tester to get hot and see if anything shows up maybe even put the heater up a notch. I tried it on the tester 7-8 v showing grid emission.

Won't be the same.

The TV has the cathode at 190v
https://frank.pocnet.net/sheets/049/6/6HS8.pdf
Max is 200v

the tester won't go that high for sure.

and you can be sure that in the set that it DOES go over 200v before everything heats up anyway.
so IF the tube is shorting, there is a good chance that it is mixing AC heater voltage with the 190v bias.
and IF it's failing then AGC is not working the way it should be, making the tuner deaf.

timmy · #**267** 09-07-2022, 04:09 PM

Sure sounds logical but would it knock out sound other then the voltage drop killing sound. Just curious if I should just wait for the tube or take a closer look at the audio.

Yamamaya42 · #**268** 09-07-2022, 06:08 PM

Quote:

Originally Posted by timmy

Sure sounds logical but would it knock out sound other then the voltage drop killing sound. Just curious if I should just wait for the tube or take a closer look at the audio.

wait for the tube, right now this all is just best guesses bases on looking at the schematic.

this is the same type circuit in my arvin.
http://suzaku.live-evil.org/arvin111.jpg

it DID a hard short.
when you lose AGC, all sorts of strange tuning stuff can happen.

timmy · #**269** 09-08-2022, 08:52 AM

I’m already contemplating the next move if this tube don’t come out a winner. If this tube was shorting then it should have been extremely hot I would think but then again didn’t have it on long enough so the hot don’t burn up.

Yamamaya42 · #**270** 09-08-2022, 09:38 AM

A tube with heater to cathode leakage/short wont get as hot as one that's overloading and running power to/from the plate, could even be colder if not conducting the way it should be, as no power is flowing from the plate as it should.