View Full Version : Color drives/biasing on '77-'80 Zeniths & '74-'75 Sonys...


fxcamera1
03-30-2017, 02:13 PM
Hello. Although I've been reading this forum for quite some time. This is my first post. I'm not a qualified technician. But somewhat tech savvy. My question today is regarding color balance(bias)adjustments. In my family we have a history of owning mostly Zenith and Sony color TV sets during the '70s and '80s. In a few of them, especially when they started to get older, the GREEN gun usually falls out of balance and emits more than the other two. Giving a greyscale program a greenish tint. When I was younger I discovered the 3 gun controls either on the back of the Sony cabinets, or on the CRT socket board inside on the Zeniths. Naturally I would think this can be solved by turning the control for the GREEN down a bit. But I have a friend who's father and brother had years of experience tinkering around with Televisions as a hobby, and to me, seemed to possess good knowledge. They advised me that this only fixes the issue TEMPORARILY. They said that the GREEN gun will eventually go back to the level it was at before making that adjustment. They also warned me that it may even get worse if I don't leave it alone, -based on one of their experiences with a 25" Sony Trinitron console set. My sister had the Sony KV-1723 Trinitron from '75/'76, and I still have a Sony KV-1722 Trinitron from '74 and BOTH sets always had the same SLIGHT "green" issue that never SEEMED to change, -I never touched those guns. We also had a 17" Zenith(model?)from 1977 and a 19" Zenith(model?)from 1980. Both those sets didn't seem to have an issue when new, but they both noticably developed a "green" issue to an annoying level as they aged. On these 2, I would turn down the GREEN, but alas the trouble would either return or worsen. After researching online and "youtubing", it seemed that it was fine to make the adjustment, but after seeing one of "shango066's"videos I learned that in some cases a relevant component for that gun going bad might be an issue. So now my Sony 1722 still has a "green" bias, and being that that control is accessible on the back, I'm asking if it is advisable to try to turn it down, or should I leave well enough alone? Thanks :-)

dishdude
03-30-2017, 03:29 PM
I think what you're asking is why do the red and blue guns get weak and the green usually stays strong?

That's always what I noticed.

Jon A.
03-30-2017, 03:44 PM
Happens all the time to Trinitrons. I had a KV-1967 from 1986 whose CRT went like this.

Electronic M
03-30-2017, 03:46 PM
Better to turn the red and blue up IMO. The aging may have something to do with the content your watching....Think of your CRT like the inks in a VERY high ink capacity printer...The color or colors that get weak first are the ones that are shown the most....Maybe you might want to leave it on the golf channel a couple hours a day? to even the wear.

The Sonys are more prone to relapse than the Zeniths.

fxcamera1
03-30-2017, 06:05 PM
I think what you're asking is why do the red and blue guns get weak and the green usually stays strong?

That's always what I noticed.

You know, that thought occurred to me. But for 2 reasons I didn't assume that because 1) This old Sony seems to have an unnatural green brightness in the lower contrast areas of a given scene and in a subjects hair when compared to my newer Sony KV-20FV12 in the next room which has a much better greyscale balance when both are compared viewing an identical source, and 2) when I saw a certain youtube video the person described one gun having higher emissions due to a component issue. Does that sound logical? -But then again, different sets can have different issues.

fxcamera1
03-30-2017, 08:24 PM
Better to turn the red and blue up IMO. The aging may have something to do with the content your watching....Think of your CRT like the inks in a VERY high ink capacity printer...The color or colors that get weak first are the ones that are shown the most....Maybe you might want to leave it on the golf channel a couple hours a day? to even the wear.

The Sonys are more prone to relapse than the Zeniths.

That's a very good analogy. Also, that's a good alternate solution about the golf channel, lol. So far it looks here like turning the red and blue up is the general consensus. The only other thing that concerns me about doing all that gun calibrating is that it may affect my brightness/contrast/color levels where they will need to be readjusted. Because if I put the auto/aft feature"on", the colors become more saturated than they should be as the set is now.

Will a rejuvenation remedy the color gun balance?

Dave A
03-30-2017, 09:43 PM
In a three gun arrangement the only things the guns can do is fade away. Others can guess why these R/B guns are suspect. Maybe the green dies later. Watching the Golf channel is a punishment that is beyond me. Maybe there is a Techincolor effect unknown to us. Unless there is some voltage variation they just fade away with age. Crank the R/B first to bring them back up. Then look at the hidden drive control which pulls all guns up or down in relation to the customer brightness/contrast controls. Remember that green is the base line for all color tv from camera to set. Single gun Trinitrons are for others to explain.

zeno
03-31-2017, 10:12 AM
You know, that thought occurred to me. But for 2 reasons I didn't assume that because 1) This old Sony seems to have an unnatural green brightness in the lower contrast areas of a given scene and in a subjects hair when compared to my newer Sony KV-20FV12 in the next room which has a much better greyscale balance when both are compared viewing an identical source, and 2) when I saw a certain youtube video the person described one gun having higher emissions due to a component issue. Does that sound logical? -But then again, different sets can have different issues.

The newer Sony has AKB ( automatic kine bias ) that adjusts itself.

On the Zenith do this.
Turn OFF the chromatic or color sentry if it has one.
Turn color down all the way.
Contrast or picture control to mid way.
Let warm up 1/2 hr.
Turn up the R & B a little to make the pix as B&W as you can.
The tube is aging so it may not be perfect.......
Return customer controls to normal & watch.

good luck
73 Zeno:smoke:
LFOD !

andy
03-31-2017, 10:51 AM
For the Sony, you also need to adjust the drive controls. Typically, they have 5 controls. three controls called background which affect the brightness of each color. They also have two "drive" controls that affect the contrast of the the blue and green (red is normally fixed at maximum because the red phosphor is the weakest). Typically as a gun ages, you need to turn down the drive to maintain good gray scale in the bright areas of the picture.

It's true that it's temporary (everything is). By the time there's a noticeable green cast, the CRT is usually getting close to the end of life, but adjustment can make it look better for a while. It won't accelerate its decline much other than the fact that the red and blue will be driven harder for the same picture brightness. Eventually the red and blue will be so weak that it's impossible to turn the green down enough to match.

I don't know why the older Sony's had problems with the red and blue guns. I don't think it's just because they are driven harder to compensate for the lower efficiency of the red and blue phosphor. Something about the gun design must make the red and blue cathodes collect more contaminants. They seemed to have mostly solved it by the late 80's. I've seen Sonys where the green was perfect, but there was virtually no red or blue. No one else had this problem consistently.

If that 25" was actually a 26", then that CRT was so bad they did a recall on it.

fxcamera1
03-31-2017, 11:23 AM
For the Sony, you also need to adjust the drive controls. Typically, they have 5 controls. three controls called background which affect the brightness of each color. They also have two "drive" controls that affect the contrast of the the blue and green (red is normally fixed at maximum because the red phosphor is the weakest). Typically as a gun ages, you need to turn down the drive to maintain good gray scale in the bright areas of the picture.

Eventually the red and blue will be so weak that it's impossible to turn the green down enough to match.


Thank you.
So basically you're saying in this case with my Sony KV-1722, I need to BOTH turn the Red & Blue BKG "up", AND the turn the DRIVE to the stronger color, in this case green,"down"?

I get what you mean by the color brightness vs color contrast though. I just want to make sure I understand how to take the right steps in this procedure as you described.

andy
03-31-2017, 03:39 PM
Thank you.
So basically you're saying in this case with my Sony KV-1722, I need to BOTH turn the Red & Blue BKG "up", AND the turn the DRIVE to the stronger color, in this case green,"down"?

I get what you mean by the color brightness vs color contrast though. I just want to make sure I understand how to take the right steps in this procedure as you described.

That's right. You want to adjust the backgrounds for neutral dark areas in the image and then adjust the drives so that bright white is neutral. They interact, so you will have to switch between them a few times. With those older Sonys, I almost always ended up with the green drive at minimum, and the blue somewhere in the middle and there was still too much green in the highlights.

The service manual does have an official procedure, but it assumes a strong CRT. With a weak CRT, you might have to compromise a little.

fxcamera1
03-31-2017, 04:46 PM
Thanks guys.

I will look for that manual and follow all these steps you all gave so far. I still welcome any more opinions if they come. I certainly have work cut out for me also because these old Sonys are tricky to get into. First I will start on the '74 Sony KV-1722. After that I will get to the '80 Zenith 19".

(The '75 Sony KV-1723 & the "77 Zenith 17" are actually gone :-(. I only included their stories because of the similar symptoms.)

zeno
03-31-2017, 06:07 PM
Thanks guys.

I will look for that manual and follow all these steps you all gave so far. I still welcome any more opinions if they come. I certainly have work cut out for me also because these old Sonys are tricky to get into. First I will start on the '74 Sony KV-1722. After that I will get to the '80 Zenith 19".

(The '75 Sony KV-1723 & the "77 Zenith 17" are actually gone :-(. I only included their stories because of the similar symptoms.)

Sony tubes of this era always have the green lasting longest. Rejuvenation
never worked. It either ruined the CRT or they looked like crap again in
a few days. Zenith CRT's until the early 90's were tough. Most mid 70's
CRT's still work at near 100% when found. It was actually a mistake for
Zenith to make them that good. TV's were never intended to last 40-50 yrs.
Ten years at best.

When adjusting the Sony follow the same basic procedure. Dont forget to
turn off any auto-color switches. Be careful of the controls. The tool can
get stuck & cause damage. They are delicate compared to the Zenith
ones with nice knobs. Also dont expect a perfect pix, just some improvement.

73 Zeno:smoke:
LFOD !

Marco-nix
03-31-2017, 10:01 PM
Happens all the time to Trinitrons. I had a KV-1967 from 1986 whose CRT went like this.


Hi, and what is the main problem when happen ?

Titan1a
03-31-2017, 11:19 PM
The red gun is usually weaker and requires more power than the others. I've found that the first gun to short-out is the red gun. Just science fact.

fxcamera1
04-02-2017, 01:13 PM
Then look at the hidden drive control which pulls all guns up or down in relation to the customer brightness/contrast controls.

What would this also be known as? The AGC? The ACC?

Would you say that I should pull them up or down according to consumer preferences? Or where I think the brightness/contrast should be according to where those front controls are at the moment I am performing this?

zeno
04-02-2017, 03:21 PM
What would this also be known as? The AGC? The ACC?

Would you say that I should pull them up or down according to consumer preferences? Or where I think the brightness/contrast should be according to where those front controls are at the moment I am performing this?

ACC is Automatic Color Control dont touch
AGC is Automatic Gain control also dont touch

Overall brightness on Zenith is affected by:
G-2 or Screen
ABL
Brite range
BL
Depends on chassis what its uses.
No need to touch them unless the pix is to brite or dark &
then it is questionable.....

Customer contrast or picture control & bright should be mid range.
Driving it at high levels exaggerate any flaws in the CRT making
it look bad.
If you take a set with a very weak CRT & adjust it in a dark room
at low level it usually will look good till you turn things up. A
slightly weak CRT can look almost good in normal light.

BTW If you post a chassis picture ( nudie ) model & chassis numbers
it helps ID the set. Dont know if you have a CC2 style steel chassis
or a System 3 style. All I know is its an in line EFL CRT.

73 Zeno:smoke:
LFOD !