Strange problem with my TV Monitor

[Barney]

Hello everybody, I have a weird problem with my TV Monitor and I thought you might be able to help me figure it out. When displaying a solid color on the entire screen with my Vic-20, the color changes hue from the top to bottom. For example, if I have solid purple displayed on the screen, the top of the screen will be red, the center of the screen will be light purple and the bottom of the screen will be dark purple.

This problem only occurs when I use my "Sears LXI", TV Monitor so I believe it is definitely a TV issue. All my other monitors and TV's display correctly when hooked up the to the same Vic-20.

Thanks for your help in advance.

[eslapion]

I looked up "Sears LXI" on Google and I can't find any TV or monitor.

Can you give more technical details ?

[Barney]

here is a post i made a while back on this type of monitor. It's basically a TV with a strange RGB input for the Commodore 128 and regular composite inputs for the Vic, C-64, etc.

http://sleepingelephant.com/ipw-web/bul ... lxi#p82774

[RobertBe]

here is a post i made a while back on this type of monitor.

Heh, I still have that extra 13" whitish LXI waiting for you.

It's basically a TV with a strange RGB input for the Commodore 128...

The IBM-style RGB input...

Leaving for the Pacific NW on Tuesday,
Robert Bernardo
Fresno Commodore User Group
http://www.dickestel.com/fcug.htm

[Imperious]

It sounds a lot to me like Your monitor needs degaussing, also known as demagnetising.
Specifically the tube.
There were various fixes for this with TV sets.

1. The degaussing components were faulty and needed replacing
2. The TV needed to be turned off at the wall for a few hours then at
turn-on the degaussing circuit would do the job. This was often caused
due to tv's being left in standby whiuch mean't the degaussing circuit never
worked, only from a full power off.
3. A degaussing wand was sometimes required if the problem was severe enough.

[Barney]

Thanks for the tip, but the degaussing didn't solve the problem. Looks like it is a picture tube issue. Oh well, thanks again.

[eslapion]

Hello everybody, I have a weird problem with my TV Monitor and I thought you might be able to help me figure it out. When displaying a solid color on the entire screen with my Vic-20, the color changes hue from the top to bottom. For example, if I have solid purple displayed on the screen, the top of the screen will be red, the center of the screen will be light purple and the bottom of the screen will be dark purple.

This problem only occurs when I use my "Sears LXI", TV Monitor so I believe it is definitely a TV issue. All my other monitors and TV's display correctly when hooked up the to the same Vic-20.

Thanks for your help in advance.

...Slap on my forehead

Do you have the same problem if you try with a C64 or another source of video signal ?

If so and since you've tried degaussing, it could mean the TV has suffered an impact and this has damaged the separation grid.

[Gyro Gearloose]

That would need a tube with a grid in the first place. It's more likely a store brand TV has a standard shadow mask.
The mask is part of the front face of the tube, it can't move, and if it did, it would affect the whole screen the same way.
It's likely the color purity magnets on the neck of the CRT have moved. You're in for a bad time trying to adjust those.
The magnets all interact and one adjustment will undo the others unless you know exactly what you're doing.

It's a bit like bicycle wheel spoke tensionning, I've seen techs adjust spokes by feel, but that's because they have years of experience.
For my bike, I need a tension meter.

This gives you an idea of what's in store
https://www.youtube.com/watch?v=QNtsTKVPO7I

Here's the trick
https://youtu.be/QNtsTKVPO7I?t=629

Even though it's an old TV in there, the idea is the same. You can make a grid pattern like that pretty easy with a VIC!

[Gyro Gearloose]

Hey, this guy is working on a modern TV and it shows what you may be seeing:

https://www.youtube.com/watch?v=nxOvYVcN1fc

[RobertBe]

This problem only occurs when I use my "Sears LXI", TV Monitor so I believe it is definitely a TV issue.

If you go to http://blog.retro-link.com/2016/11/comp ... s-lxi.html , you can see what a VIC-20CR outputs to a 13-inch Sears LXI. Just click on the picture to enlarge it.

FCUG celebrating its 35th anniversary,
Robert Bernardo
Fresno Commodore User Group
http://www.dickestel.com/fcug.htm

[Barney]

Thanks everybody for the help. I think I know what the problem is. I think it is a bad solder joint somewhere on the board. I noticed that when I gave the monitor a tap the color corrected for a moment until I adjusted the knobs below. I think the slight vibration on the motherboard as I adjusted the knob caused it to change back. It looks like I need to find what needs to be resoldered.