Westinghouse TV no picture : Strip or fix?

[electroking]

Hello again,

I don't think this has been suggested before. The cathode current of
the 12BY7A video amplifier is supposed to go through R-221, the contrast
control potentiometer. If there's anything wrong here, no video signal
will get to the CRT cathode.

With the set off, just pull the 12BY7A tube, connect one terminal of
your ohmmeter to ground and the other to pin 1 at the tube socket.
While rotating the contrast control, you should get a smooth variation
between 0 and about 500 ohms. If this is OK, fine, otherwise the
control should be cleaned, replaced, or temporarily replaced with a
resistor of about 250 ohms.

Once the previous check has been completed, you may reinstall the
video amplifier tube, power up the set and check the DC voltages on
the tube: +178 on plate (pin 7), -2 on control grid (pin 2) and +161
on sceen grid (pin 8). Note that schematic seems to be indicating the
-2 volts on suppressor grid (pins 3 & 9), but that does not make sense
as this grid is grounded. I do believe that the -2 applies to pin 2.
If anything is odd here, get back to us and we'll discuss.

If you have good sound, it means that the problem is somewhere
between the video detector (V-5B) and the CRT cathode, and
things are not that complex in this area. Bye for now.

[JesusJones]

Sounds like a plan.

I will also be changing the horiz output tubes cathode resistor.
It checks in at 120 ohms and should be 150. Might this help some other voltages get in spec. Such as the 3au6 and 3cb6.

[jpdylon]

how are you checking the resistors?

If you measure them while they are in the circuit, you almost always get a lower value because of the resistance in parallel with that one (tube elements, caps, etc) Unsolder one leg of the resistor and then check it. You'll find that the values will be MUCH different.

Usually when resistors begin to fail they will go UP in value, not down. Chenging the cathode resistor in the HO circuit will NOT change the voltages in the IF stages. If voltages are low its due to a power supply problem or something pulling down the voltage in the IF stage like a shorted capacitor or tube.

Do you have a tube tester?

[JesusJones]

Yes I do have a tube tester. B&K model 606 tests if its good or not, shorted, or if its grid is leaking/or gassy it claims. It works but I am not sure of it's accuracy(needs fine tuning I'm guessing but it works).

Most of the resistors I have checked have capacitors or something blocking them off from any parallel paths and what not. Or would this still be way off.

The 470 ohm resistor that goes to pin 2 of the video amp checks in at 530 ohms

The path from v5 to v6's first grid also checks in OK. Although I noticed there is no resistor in parallel with the second inductor after pin 8 from v5.(Change in production?)
Oh and the contrast 500 ohm resistor is fine. It makes the screen brighter and duller as of right now.

And the horiz. output gets it's voltage from the flyback trans. At the bottom it has connections 1 and 2 that go off to the left and go to the plates and cathodes and grids of some of the tubes? Does the current the horiz output draws affect those voltages.Or are they not connected in that way.

Voltage Readings soon tomorrow




Hehe Racoons keep waking my dog up then she starts barking. So I go outside with a bucket of cold water (and it's already cold out) and..well.. you can imagine the rest. They Don't Like That.

[electroking]

The winding with terminals 1 and 2 of the flyback provides pulses to the circuitry
that synchronizes the horizontal oscillator frequency to that provided by the
sync pulses in the received signal, in order to achieve correct horizontal sweep.

[JesusJones]

Well I checked the voltages.
Pin 8 had 170 .
pin 2 had -220 volts , measured from grid to ground.
pin 7 had 161 volts

Sort of the reverse of what it should be
Although I did not adjust the contrast at all during that test. Afterwards I tried again on pin 7 and could vary it beyond 180.

What about that grid though?

[electroking]

Originally Posted by JesusJones

...
pin 2 had -220 volts , measured from grid to ground.
...
What about that grid though?

If you really got such a big negative voltage at the grid, no wonder
the tube doesn't pass the video signal. Are you confident about this
measurement? It's hard to believe.

Did you check the contrast control operation with the tube removed?
I guess so since you proceeded to measuring these voltages.

[JesusJones]

Yes the 500 ohm pot is doing just fine. So I did the other tests.

And sorry It's this new tester I got. It said -200mv (still getting used to it). But shouldn't it be -2000mv.

What should I be checking to get this right?

The cap marked 400v should be .1mfd

[electroking]

Well, all the discrete components that are connected to V-6, in particular R-222
R-231, R-229, R-232, C232. The capacitor C-232 is only marked 400 V,
without capacitance, maybe you can locate it on the PCB and identify
it. You might bridge it temporarily with a similar one, without removing
the original. Be careful with those old PC boards, they were fragile even when
new!

Maybe you could try new tubes for V-5 and V-6, although the presence
of sound suggests that they are working.

I'm getting puzzled. Any other ideas, fellow AKers?

[JesusJones]

The cap marked 400v should be .1mfd

And I'm gonna ask this one more time. The height control pot. What is it's resistance supposed to be. This pot is checking in very oddly with me

Is there any chance I put an electrolytic in wrong, or that one is not functioning. And that this is causing ac to scramble the picture or something like this. I tried setting my voltmeter to ac on the dc line and it gave me alot of ac.

[electroking]

Originally Posted by JesusJones

The cap marked 400v should be .1mfd

And I'm gonna ask this one more time. The height control pot. What is it's resistance supposed to be. This pot is checking in very oddly with me

I read 2.5 Megohms, that is 2 500 000 ohms and it does feed the plate of
V-14B with DC so it should be in good condition for proper vertical sweep.
However, the problem of the video signal not reaching the screen is
probably unrelated to this.

[JesusJones]

That pot has nearly 6 megs on it.

Some one had said before that the heater on the crt could be shorted somehow causing horizontal hum bars. What would these look like.

And its very strange. The tv shows snow on a static channel. If i looked at the tv in someones living room I'd say it was snow. But you tune it to a channel and it starts having bars and stuff again.
/
Tuning the horizontal control at the front of the tv makes these bars go ___/ the other way they go straight -------

Could the screen also be scrolling vertically at a high rate?

ANd I noticed that the audio output tube and the vert output tube get noticibly hotter than the rest.
If this overheating were not due to the voltages on the tubes, could it be some sort of oscillation that I can't see or hear

[electroking]

Originally Posted by JesusJones

That pot has nearly 6 megs on it.

Some one had said before that the heater on the crt could be shorted somehow causing horizontal hum bars. What would these look like.

And its very strange. The tv shows snow on a static channel. If i looked at the tv in someones living room I'd say it was snow. But you tune it to a channel and it starts having bars and stuff again.
/
Tuning the horizontal control at the front of the tv makes these bars go ___/ the other way they go straight -------

Could the screen also be scrolling vertically at a high rate?

ANd I noticed that the audio output tube and the vert output tube get noticibly hotter than the rest.
If this overheating were not due to the voltages on the tubes, could it be some sort of oscillation that I can't see or hear

6 Megohms is definitely out of spec. That pot will have to be replaced.

What you're getting on the screen when you tune properly is likely
to be the correct video signal, with inadequate vertical sweep. The
effect of the horizontal hold control does appear to be normal.

So the area that needs attention is moving again to V-14 and V-15.
In addition to the height control, you have two more pots in that area
(R-422, linearity control, 800 Kohms and R-416, V. hold, 1.5 Mohms).
Every part in this area, including that capacitors, must be in good
condition so that the oscillator will free run at the approximately correct
frequency and will synchronize with received signal.

Since you don't have a 'scope, here's a trick that might help you
troubleshoot the Vertical sweep circuitry. If you can dig a cassette
recorder equipped with a loop designed for recording phone calls, and
get the machine to work in the 'tape monitor' mode (feeding the
signal being recorded to the earphone), you might first determine
that you can pick 60-Hz hum from single wire carrying AC. Then,
bring the loop close to the vertical ouptut tube and associated
circuitry. The waveform here is not a sine-wave but some kind
of sawtooth wave, but it should have the same fundamental frequency
of 60 Hz. If you hear something higher-pitched, you know something
is wrong.

The V. output and audio output tubes do dissipate a lot of power, so
the heating you are observing is probably normal.

As for hum bars, you would see two dark horizontal stripes on the screen
separated by an approximately equal height grey stripe. But since the
heater string is grounded at the CRT end, and you already measured the
cathode voltage to be correct at about 113 V DC, I don't think you need
to worry about this. Good luck.

[JesusJones]

Originally Posted by JesusJones

That bumble bee cap must have been a replacement or something.(Its the only one in the whole set) It says it is rated at 60000pf If I did it right. (From the point with solder,Blue, black, orange, black, brown) This would be .06mfd.
Which makes me ask again. Is the cap just above v-15(12b4a). Rated at .0547(or is that unheard of) or .0047 as previously stated.

That bumble bee cap is just above v-15. Was .0547 the right value to replace it with?

And I will work on the rest of the things in this area. ALso that pot.

[electroking]

If you mean C-404, I read 0.0047 microfarad. This feedback loop made of C-404, R-425, R-419 and C-407 is quite critical for the vertical ouput circuit operation.
Good night.