Are these things I should consider bad

[Electronic M]

The CRT shields on Zeniths of that era almost completely hide the dag. I should know I have at least two Zeniths that use that CRT shield.

[jr_tech]

Originally Posted by Electronic M

The CRT shields on Zeniths of that era almost completely hide the dag.

Good enough! I have never seen one in person and thought that the HV filtering (and ringing suppression) would be really poor if it were missing from a sloppy re-build job or from somebody cleaning all that "dirty stuff" off of the CRT.

jr

[old_tv_nut]

Originally Posted by Electronic M

The CRT shields on Zeniths of that era almost completely hide the dag. I should know I have at least two Zeniths that use that CRT shield.

thanks for this comment - made me look again, and I now see that apparently the picture shows the internal dag (?). If the external only is underneath the shield, then it is probably OK because none of the external components, labels, etc. are disturbed.

I still think the dag is a wild goose chase for anything having to do with the jail bars (isn't that the one thing we are trying to fix here?).

Need to stop shot-gunning and try to follow clues - there is a jail bar pattern in at least some of the CRT leads, and there are questions as to why some of the waveforms are fat (high frequency or low frequency superimposed?). Should be chasing down if those scope waveforms are valid and going from there.

[TinCanAlley]

Originally Posted by old_tv_nut

thanks for this comment - made me look again, and I now see that apparently the picture shows the internal dag (?). If the external only is underneath the shield, then it is probably OK because none of the external components, labels, etc. are disturbed.

I still think the dag is a wild goose chase for anything having to do with the jail bars (isn't that the one thing we are trying to fix here?).

Need to stop shot-gunning and try to follow clues - there is a jail bar pattern in at least some of the CRT leads, and there are questions as to why some of the waveforms are fat (high frequency or low frequency superimposed?). Should be chasing down if those scope waveforms are valid and going from there.

I'm ready and willing to do any testing you guys come up with. I'm going to disconnect the lead for the setup side of the setup switch to see if there's some kind of issue in the switch. It seems to be a pretty basic open design switch, so I cleaned it with Deoxit. That didn't help as I still have the bars and I still can't get a setup line from the red or green and only a faint line from the blue.

[TinCanAlley]

Never mind. I missed a couple of points of connection, so I'll have to start over. I thought I was able to delete posts, but I don't see how.

[TinCanAlley]

Okay, spent the better part of today looking into why the setup doesn't produce a line. This is what I found out, but not why or how to fix.....

The G1 voltage controls brightness and the higher the voltage, the dimmer the output. The voltage should be around 142V for normal and actually measures out around 147 - 150V. That's not too bad. It's when the setup mode is entered that things change. The voltage of the G1s goes up to 190V and that must be why I can't see the lines when adjusting the G2. 190V is making it too dim to see.

Now why the voltage goes up that high is beyond me. I looked over the schematics and see an 18K and a 1.8K resistor on the setup side of the switch and am not sure if one of those (or a combination of both) could account for the voltage difference.

[old_tv_nut]

Originally Posted by TinCanAlley

Okay, spent the better part of today looking into why the setup doesn't produce a line. This is what I found out, but not why or how to fix.....

The G1 voltage controls brightness and the higher the voltage, the dimmer the output. The voltage should be around 142V for normal and actually measures out around 147 - 150V. That's not too bad. It's when the setup mode is entered that things change. The voltage of the G1s goes up to 190V and that must be why I can't see the lines when adjusting the G2. 190V is making it too dim to see.

Now why the voltage goes up that high is beyond me. I looked over the schematics and see an 18K and a 1.8K resistor on the setup side of the switch and am not sure if one of those (or a combination of both) could account for the voltage difference.

Something's wrong with your measurements - either you are not measuring G1, or something else is going on.

G1 voltage higher = more brightness. Cathode (K) voltage higher = less brightness. It's mainly the difference between cathode and G1 that controls beam current, so you have to measure both to figure out what's happening.

These voltages *should* change to a predetermined value when you go to the setup mode, so that you can set the G2s for proper cutoff; then when you go to normal, the signals on the cathodes and G1's will produce the right colors.

[TinCanAlley]

Originally Posted by old_tv_nut

Something's wrong with your measurements - either you are not measuring G1, or something else is going on.

G1 voltage higher = more brightness. Cathode (K) voltage higher = less brightness. It's mainly the difference between cathode and G1 that controls beam current, so you have to measure both to figure out what's happening.

These voltages *should* change to a predetermined value when you go to the setup mode, so that you can set the G2s for proper cutoff; then when you go to normal, the signals on the cathodes and G1's will produce the right colors.

This is what I got out of a book on CRTs.

"The control grid (G1) controls the brightness of the CRT. It is generally
placed directly on top of the cathode. If there is no voltage on G1, the
electrons can flow freely from the cathode. If there is some negative voltage
on G1, the electrons from the cathode are repelled somewhat, and the screen
appears darker. The greater the voltage on G1, the darker the screen becomes, because more electrons reaching the screen equals a brighter image, and less electrons hitting the screen equals less brightness."

I'm attaching the CRT section of the schematic. If I have the G1 information incorrect, I need to know. My understanding is pins 2, 11 and 6 are the G1s. I'm also attaching a pic of a chart from a CRT tester manual.