Mighty Monarch of The Air

[vts1134]

Originally Posted by old_coot88

Well, while waiting for the heavy artillery, if you're game to try the 'quick & dirty' method of signal injection, here's how i would do it -
Tie onto the 6.3V heater supply just like you did earlier for the vertical, except this time put a cap in series with the clip lead. Value isn't critical, anywhere from .01 to .1 is OK. This'll give you a DC-isolated 60 cycle signal for injection.
Start at G1 of the CRT (pin 2). The raster should show a mild hum bar. Now hit the plate of the video output stage (pin 6 of the 12AU7). The same hum bar should appear. Now hit the grid (pin 7). The hum bar should show quite a bit of amplitude gain. Now hit the plate of the 1st video stage (pin 1 of the 12AU7). It should show the same amplitude gain.

Now to inject at the grid of the first video stage, it's a good idea to attenuate the signal so as to not overdrive the video stages. So let's utilize the 8.2K resistor (R27) that's already in place between the grid (pin 2) and ground. Add an 82K resistor in series with the cap on your clip lead, so that this new resistor is now the "probe". When touched to the grid (pin 2), it's also in series with R27 and forms a voltage divider giving a little over 10X attenuation. So the grid will be seeing about .59 VAC of signal. Of course you can reduce the value of the new resistor to give less attenuation if desired. {Those two coils L10 and L11 can be considered zero ohms in this situation.}

As a precaution, i would leave the diode M4 disconnected during the procedure.

So if you lose the signal at any point while working back stage by stage, that will isolate where the failure is at.

oc

Can I use the signal generator for all of the above steps? Starting with G1 of the CRT and working back to the detector diode. I'm guessing that anything after the video amp will not give me anything like a picture, but should give me some change in the raster, and anything before the video amp (assuming the failure is upstream) will give me the full pattern. Am I right?

[old_coot88]

Originally Posted by vts1134

Can I use the signal generator for all of the above steps?

Sure, absolutely.

Starting with G1 of the CRT and working back to the detector diode. I'm guessing that anything after the video amp will not give me anything like a picture, but should give me some change in the raster, and anything before the video amp (assuming the failure is upstream) will give me the full pattern. Am I right?

Well, when you hit G1 of the CRT (with the genny's output set high enough to see the signal), you should see whatever pattern the genny is set to. It might be negative though (that is, just like a photonegative). As you work back, you should see gain when you hit the grid of the video output stage (pin 7), and attenuating the genny as as needed, more gain at the grid of the 1st video stage (pin 2). This'll confirm that the video stages are working.
As mentioned before, since the detector diode is so easy to get to, i would leave it disconnected as a precaution against zapping it with the probe.

You'll probably see the pattern phase-invert (ie., shift from negative-to-positive) as you work back. That's because a tube's plate is 180 degrees out of phase from the grid. Grid goes positive, tube conducts more, pulling plate voltage down. Grid goes negative, tube conducts less, allowing plate voltage to rise.
oc

[vts1134]

Originally Posted by old_coot88

Sure, absolutely.

Well, when you hit G1 of the CRT (with the genny's output set high enough to see the signal), you should see whatever pattern the genny is set to. It might be negative though (that is, just like a photonegative). As you work back, you should see gain when you hit the grid of the video output stage (pin 7), and attenuating the genny as as needed, more gain at the grid of the 1st video stage (pin 2). This'll confirm that the video stages are working.
As mentioned before, since the detector diode is so easy to get to, i would leave it disconnected as a precaution against zapping it with the probe.

You'll probably see the pattern phase-invert (ie., shift from negative-to-positive) as you work back. That's because a tube's plate is 180 degrees out of phase from the grid. Grid goes positive, tube conducts more, pulling plate voltage down. Grid goes negative, tube conducts less, allowing plate voltage to rise.
oc

When I inject video directly on pin two of the crt I am getting nothing more than the slightest change in raster. There is definitely not any sign of the pattern that the generator is outputting. There is control for phase +/-, adjusting this gives slight changes in the raster. When that control is left in the 12 oclock position there is no change in the raster from the generator in the off position.
I am using a piece of wire wrapped around pin 2 of the crt to attach my video output test lead to, and the negative test lead I'm attaching to the chassis.
I've also hooked up the generator to my living room tv's composite input and verified that the generator is in fact outputting a signal.

Is there some other way to verify that the crt is ok?
Could the signal be too high or low coming out of my generator to give a full picture when connected directly to pin 2 of the crt?
Will there be a party when this is all over that every one is invited to?

I can only answer the third one.

[old_coot88]

Originally Posted by vts1134

When I inject video directly on pin two of the crt I am getting nothing more than the slightest change in raster. There is definitely not any sign of the pattern that the generator is outputting. There is control for phase +/-, adjusting this gives slight changes in the raster. When that control is left in the 12 oclock position there is no change in the raster from the generator in the off position.
I am using a piece of wire wrapped around pin 2 of the crt to attach my video output test lead to, and the negative test lead I'm attaching to the chassis.
I've also hooked up the generator to my living room tv's composite input and verified that the generator is in fact outputting a signal.

What about if you inject at pin# 7, the grid of the vid.out stage?

Is there some other way to verify that the crt is ok?

The jug appears to be OK if you're getting a decent raster and the brightness control works as it should.

Could the signal be too high or low coming out of my generator to give a full picture when connected directly to pin 2 of the crt?

Too low, maybe. Too high not likely at all.

Will there be a party when this is all over that every one is invited to?

I'll bring the beer.

[vts1134]

Originally Posted by old_coot88

What about if you inject at pin# 7, the grid of the vid.out stage?

Ok, here is the worlds worst youtube video .
http://www.youtube.com/watch?v=wqO0pCZS8gU
I used two different patterns. The first was one horizontal line, the second was one vertical line. I adjusted the phase from all the way positive to all the way negative on both patterns. Please forgive the angle of the camera.

[old_coot88]

So what happens if you inject at pin 2, the grid of the 1st video stage (with the diode disconnected)?
Have you actually checked the diode with an ohmeter? It's a very elderly germanium diode, and should show a very high (though probably not infinite) resistance in one direction and a much lower resistance in the other direction.

[vts1134]

Originally Posted by old_coot88

So what happens if you inject at pin 2, the grid of the 1st video stage (with the diode disconnected)?
Have you actually checked the diode with an ohmeter? It's a very elderly germanium diode, and should show a very high (though probably not infinite) resistance in one direction and a much lower resistance in the other direction.

The diode reads 35k in one direction and 1.5k in the other.
There is no change in raster when I inject at pin 2 of the 12au7.