Alternative Way of Adjusting G2s (25EC58)
 

After cleaning the setup switch I am now able to get a line on the screen for blue with 3/4 turn, but not for red or green. If I go back to normal mode with an image in B/W (color turned down and brightness half way) I can see each color as I turn the controls. Color starts appearing after about 1/4 turn. I adjusted until I got a decent grey scale image. From there I adjusted the taps to remove the slight red in the light areas.

While this has produced a good image and color, I don't think it's the best for the tube if I don't have them set right. I'm wondering if there is a better way? Voltage level?

I'm not sure why the other two G2s can't produce a line. When I last checked the tube it tested good. Should I test it again as it's been 12 years.

The factory recommended manner of adjustment are for the most repeatable and stable mode of adjusting it, but cannot be the only way. I have one TV where the red gun are only a bit weaker that others, and I simply adjusted with a B&W image at low bright settings, and repeated for low light scene/image with normal bright position of usage. Worked like a charm. Only a little deviation from the original positions. A more distance from original adjustment means weak CRT or some kind of issue in the circuits.

It's been at least a couple of years since I messed with grey scale on a CCII. Generally on Deltagun CRTs the instructions will say to minimize brightness, flip service switch and turn down G2 controls. If one or more guns doesn't produce a line at max G2 increase bias or brightness range pot to until dark guns produce light at max G2. if neither pot/switch exists in circuit (they aren't always in a convenient/obvious location so check schematic) advancing brightness is allowable. Once all are able to make a dim line bring up red to barely visible, bring up green to make the line yellow, bring up blue to make line white, return service switch and brightness to normal positions and if necessary touch up color drive pots for good white balance.

I know it doesn't take much advancement of the G2s to bring up color in a B&W image, so I'm assuming the CRT is working well. Why that same advancement doesn't produce a line is beyond me.

The only adjustment related to brightness I can find is the Brightness Limiter (other than the brightness user control). I guess I can do the adjustment procedure as it might have drifted from what I did 12 years ago.

I am trying my best to trace the setup switch in the schematics, but I think in setup, it disables brightness control. When I bring up the blue line, advancing the brightness control has no affect on its intensity.

Okay, I did trace the setup switch. It seems when switched, and I'm over simplifying this because I know there are other changes such as vertical, it disconnects the contrast and brightness circuits and connects the red video output to the brightness limiter circuit. I'm attaching a couple small images of the two circuits it connects with a red line showing the setup path.

A tiny tweak of G2 should adjust relative color level a bit on normal viewing. It's absolutely possible to still have that effect on a normal picture but no setup line...that happens when the gun bias voltages (cathode, G1,G2) are wrong or when the CRT is weak. If the cathode to grid voltage difference has the grid too negative or G2 isn't able to reach the B+ boost voltage feeding the one end, or the HV is below rated level that all could cause it.

I'm not sure how the schematic snippits you show relate to the service switch. You show the brightness limiter hooked to the Red video transistor but it probably interacts with all 3 color video transistors through paths that can't be fully seen in the snippits.

If you have a DMM and a CRT tester that's known working check the CRT and check the voltages feeding it. Maybe write them down and report back on the voltages VS schematic.

I used to have a Zenith 4-tube hybrid (basically a CCII flat chassis chassis but with tube horizontal sweep) with a bad CRT previous owner got it used in the mid 70s and it was his main daily watcher TV until 4 years ago. Two of the guns couldn't produce a line and I think I just turned off color and did what I could with color at minimum and a full screen grey scale pattern. It looked ok as long as adjusted several minutes after warm up after gun emission drift stopped.

The service switch isn't a rare part and I have seen dead ones completely kill raster in both positions...I just replaced the switch to cure the problem.

The parts of the schematics I showed how the setup switch connected those two circuits together. I'm assuming the switch when connected to the brightness circuit kills the brightness control and on the video side, I don't know what it does to that circuit. I could post the entire schematic, but with the size limitation here, it wouldn't be very readable.

I do have a B&K 470 with correct socket. I'll test the tube. I'll also get my small clip-ons for my DMM and test voltages. I'm assuming the best place to do that is directly to the CRT pins?

Just tube through entire test and it is in great shape. So now it's on to voltage testing. I'll scan back through past posts as I recall doing something similar back in 2013. Will be interesting to see what I get now compared to back then.

Just went over past posts from 2013 and found one I completely forgot about and it was never answered (the thread stopped after one other post). Guess I gave up, but now that I'm back in fix it mood, I want to continue.

I hope this link works, if not I'll copy and paste.

https://videokarma.org/showpost.php?...&postcount=188

This discovery was just verified today. I still can produce the lines if the taps are removed from the video drivers. Gotta be something to that.

I will give this a try as testing the CRT puts it as being good and I don't want to push it harder than it should be so I lasts as long as possible.

So when I do this I should turn the brightness control down to a very low level, but the image should still be visible for adjusting. Contrast matter? Then once I adjust for a good grayscale, I turn up the brightness to a normal level and readjust the guns.

I've done it with just a black screen - like you sometimes get with a modulator with nothing hooked to the input, or a DVD player turned on, but with no disc in it -- The black will look a little too red, green, or blue depending on which is set too high. With this method you can set the controls too low though, so you want to start with the controls a little high, then turn them down till just when the black screen stops looking too red, green or blue, but no lower.

Ideally, the lowest light setting is a perfect grey, and the whitest bright setting is pure white.

In theory, you're tracking will be right on if you do that. In reality, the demodulation is going to play a role in between, so if that's off, then the stuff in between is going to be off, then color balancing isn't going to fix it.

Always good practice to turn color to minimum during grey scale adjustment. If color demodulation adds significant tint where it shouldn't at normal color level then you probably need to service the demodulator.