Chromacolor II CRT setup - black level and white level?

[N9ZQA]

All -

Got a question about grayscale setup on a Chromacolor II (25KC45 chassis). I've looked in a few different places (books, Internet, etc.) and everyone seems to have a different procedure for doing this.

In the past, I've done setup on this set by setting the 'black level' knob to the center of its rotation (it's got a built-in detent), the 'picture' or contrast knob to about 60-70% of its rotation, flipping the service switch, and adjusting all three screen controls for a 'barely visible' (the only common thing I've read in all procedures!) white line.

This results in a great looking monochrome picture, although the black level seems a little high (i.e. when my DTV box is on a no-signal channel, there is a black screen, but the TV reproduces it as a slight gray). Not too serious, but if I turn the black level knob down a bit, the black becomes true black. Whites still look OK.

Where do the brightness and contrast controls usually get set during this procedure? Is there possibly a certain procedure for this chassis? Since this set gets used quite a bit, I'd like to make sure I've got it set up correctly.

-Jim

[andy]

000

[N9ZQA]

I'll have to try it and see; one of the books and a couple of the Internet sources mentioned that the brightness and contrast played a role in the setup-line-twiddling, but a couple other sources state it doesn't.

The picture starts off dim but watchable, and comes up to normal brightness in about 5-10 minutes. I still have to chase down an intermittent flicker of the brightness, but seem to have that localized to the front control panel. It doesn't seem to do it when the set is fully warm, though.

Do these sets ever produce a fully black picture with no video? Maybe I'm just expecting too much from it?

-Jim

[julianburke]

Your procedure is a proper one and a very similiar way the Zenith field engineer (Jack Van Hutton) taught me to do.

[old_tv_nut]

This set may not have full DC restoration, and therefore will not go completely to black on an all-black image (but I am not sure at what point most sets including Zenith went to 100% DC restoration). This was a perennial complaint of Consumer Reports for years, that sets should have full DC restoration.

[N9ZQA]

Thanks to all for the responses!

Sounds like I'm on the right track; I think I might do a little more experimenting after the holidays to get a better handle on things.

I picked up a copy of 'Basic Television Principles and Servicing' by Bernard Grob at our local junior college's last book sale and have been trying to understand how this thing actually works.

-Jim

[kx250rider]

I can't remember if they had moved the G2 pots to the CRT socket board by then, or was it still 3 pots below on the chassis? There's also a sub brite pot, which I think is active even during service position.

If it's the old one with the pots on the chassis, make sure the G1 jumpers are on the center lug on the video output module (follow the CRT socket leads). Turn all G2 pots to minimum, and throw the service switch. Try them 1 at a time, and you should get a line at about 30% clockwise. If it's too early/late, you can adjust the CRT Bias or Brite Limiter pot. Then set the 3 G2 pots for a faint gray line. Bring the picture back, and turn the picture (cont) to minimum and brightness/black level to where you just barely see a faint picture (Chromatic switch off, if it has one), and see how the white balance looks. Correct it with the G2 pots if needed, then set for a normal B&W picture and use the G1/drive pots or jumpers to correct the bright areas of the picture.

That procedure is mine; didn't come from any official manual. Done it at least 2000 times since the 70s

Charles