Motorola roundie

[timmy]

Well checking resistors not coming up with anything wrong so I went and tested tubes in the color circuit and all I found was the burst amp tube had some grid emission but as it heated up the grid emission lowered so I had another used one with no grid emission and now the color is syncing and if I change the channel momentarily I get the color bars again and then it seems to lock in on it’s own so maybe the problem here is tubes even though they test good it can’t be believed that they will work right.

[Alex KL-1]

Originally Posted by Electronic M

Back in the day TV techs used to find thermally dependent faults with freeze spray. Get some canned air or that old radio shack tuner cleaner that is basically oil that comes out of the can frozen and with the set on and the chassis jigged so you can access everything in the circuit with it running hit every component in the offending circuit a few at a time once warm and see which component when chilled puts it back to the cold operation state, once you find a region of the circuit that effects it narrow your chilling until you isolate the exact part that's causing it.

About thermal related issues, like the original in thread (seems to be tube related as the last timmy's posting), I have sucessfully finally solved the the mystery of my Telefunken TV, using a electrical cleaner spray. I discovered (well, remembered... thanks to Electronic_M tip) this spray cooled surfaces, so I can try on this TV (when finally I had the time). One vertical output transistor reacted to it (thermally)(a TIP31), and, I discovered some hygroscopic resistor in series with the vertical centering control, and/or in the feedback arm... exactly what one I don't had the patience to discover; I changed all ones at the smalles area I can apply the spray (only 4 resistors). Super stable after this.

[timmy]

What’s the best grease or solvent to use on tube pins to help continuity. Or tuner spray?

[Electronic M]

Originally Posted by timmy

What’s the best grease or solvent to use on tube pins to help continuity. Or tuner spray?

Tuner/contact cleaner should be fine.

[dtvmcdonald]

Contact cleaner will usually help. DeOxit is usually better. I like the brush-on
kind as its not messy.

I usually clean pins first with the green dish scouring pads.

[timmy]

Well it wasn’t tube pins one moment the color syncs just fine then the next day it won’t sync at all. I don’t know if the 3.58 xtal may have drifted a bit enough to keep the color from syncing.

[Yamamaya42]

You are dealing with an absolute here as far as the quartz crystal goes, it works, or it does not, it can not drift from it's designed frequency, any problems with the reference oscillator will be in the secondary or tertiary circuits of the crystal.

If there was a problem with the primary area of the crystal, it most likely would not be running at all.

[timmy]

What I have noticed is that the 6aw8 tube is exceptionally hot for only being on for less then 3 minutes and the color killer don’t seem to kill the color once it’s in sync. That tube is the color killer and tried another tube and the same result.

[Yamamaya42]

There is hardly any power on the triode part of the 6AW8A (killer), and little or no effect should be seen by turning color killer in color video, perhaps it may fade the color a bit, but drastic reaction should be seen with color fringes in B/W video, or fake coloring in snow with no signal.

V4 is also first video amp, a sharp- cutoff pentode, this part IS doing a lot of work, so getting hot fast is nothing unusual.

[timmy]

I just remember my other color sets with a color picture turning the killer counter the color disappeared.

[timmy]

And no I don’t have a scope so I guess it’s off again looking for bad resistors as I haven’t found not one bad one yet in the burst area, sync phase detect and chroma reference osc. So from here I don’t know where next.

[Yamamaya42]

If there is any doubt, replace with new 2% resistors, this will remove any chance of them changing value as the get hot/cold, even if they seem “OK” you can't account for how they will behave with temperature, pay vary close attention to R171/R172, these should be a matched pair, the higher the tolerance, the better, a matched pair will get you a more stable lock.

[timmy]

Originally Posted by Yamamaya42

If there is any doubt, replace with new 2% resistors, this will remove any chance of them changing value as the get hot/cold, even if they seem “OK” you can't account for how they will behave with temperature, pay vary close attention to R171/R172, these should be a matched pair, the higher the tolerance, the better, a matched pair will get you a more stable lock.

I do remember those 2 resistors and they were almost the same very little difference between them. What’s really odd is that the color seems to sync at random hot or cold now.

[Electronic M]

Originally Posted by timmy

What I have noticed is that the 6aw8 tube is exceptionally hot for only being on for less then 3 minutes and the color killer don’t seem to kill the color once it’s in sync. That tube is the color killer and tried another tube and the same result.

You do realize the color killers function is to look for the color burst in the recieved sync signal and turn the color off if there is no color burst in the recieved program, right?

There's basically nothing out there designed to send monochrome programming without a burst running* so the killer should naturally be in the color circuit enable state all the time.

* Some people with monochrome TVs will chop up a cable so they can take the luminance coax from the S-video output of a device and use that for burstless high resolution monochrome, but it seems pointless to do for a color set.

[Username1]

Just to re-enforce what EM said the Color Killer to basically a do-dad that turns off
the color osc, & other color circuits when you are watching a B&W tv show. It was
found that if those circuits were not turned off while a B&W show was on, it produced
annoying color effects outlining items, or characters on the screen. One way to
Properly adjust the color killer knob is to turn to a channel broadcasting mosquito
races and turn the color killer knob until the races are only B&W. When you
switch over to a color program, it should work as normal & you see the
program in full color. Mosquito races can be found on any analog channel
that has no programing being broadcast.

I did not see any confirmation that this is that same Motorola TS-907 that you
have worked on before, but I suspect it is..... If the Local color osc. does not
sync with the burst signal coming in on the tv signal, you will get that
"barber Pole" effect on the screen. You should look over at the V21,
V22, & V23 tubes & that area for possible troubles.....
As always, without a scope, starting off with
voltage checks is the best idea, If all is
well with that, you can always tweek
coils, but document each move
down to the smallest mm.
And try to put them back
if it don't get better.
Remember 6GH8
Tubes are trouble.



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