Zenith Chromacolor II "Ghosting" Problem

[ghjkl67]

My Zenith television with a 25EC58 chassis has a ghosting picture. What I mean is NOT multiple images. You can see in the pictures that the people have a distinct black outline on the left side and a white outline on the right side. On one of the pictures, you can see that the horizon actually goes through the person's body in the foreground. Somethimes, the outline thickness is enough to completely wash out a small image, such as subtitles on TV commercials. I noticed that this problem mostly comes up when there is a large contrast of light in a single frame, such as adark object on a light background.

My guess is the AGC Delay, but I tried adjusting it with no success. I noticed when I move the dial all the way clockwise, the outlines become thicker (with a fuzzy snowstorm). Also, the intensity varies depending on what picture is shown. I hooked up a cable box to the TV, and the picture looked fine when I turned the weather report on. When I turned on a hockey game, the picture got completely washed out. When I connect a VCR, the picture almost always starts to "ghost". Another reason I think the AGC Delay is part of the problem is because the picture tends to swerve at the top of the screen. Again, instensity depends on what movie I put in. There is no problem with the tape or VCR (it was tested on another TV). Occasionally, the picture divides the colors into horizontal stripes across the screen (see picture). I usually fiddle around with the tuner and AGC delay to fix it, but after I fix it, it appears again when I change the channel momentarily, and back again.

Please note that the color issues and swerving picture are not major problems, they only come up from time to time. I thought it may help knowing that to diagnose the initial problem (the ghosting). Also, the AGC Delay might have nothing to do with it. Based on what I know about this TV, it is just an educated guess. Please let me know your thoughts on how to resolve this issue.

Take a look at this link to a forum on antiqueradios.com about the same TV if your interested. You can reply on this videokarma posting if you would like.
http://antiqueradios.com/forums/view...p?f=3&t=189977

[DaveWM]

if the ghost is not tunable,then maybe an open peaking coil, like the one before or after the delay line, you should be able to check them with an ohm meter.

Find the delay line (large tube shaped coil) and check it and the peaking coils attached to it for open. The signal would still get thru the various shunting resistors from the 2nd to the 3rd video amp.

[old_tv_nut]

Does this set have an automatic fine tuning (AFT/AFC) switch? What happens if you turn it on or off?

[ghjkl67]

It does have an auto fine tuner. I tried it both on and off. No results.

Could you help me locate the delay line? Is it the large silver capacitor (about 5 in. high) on the left side of the chassis? How do I check with an ohm meter?

[DaveWM]

You should see a long tube shaped coil (will not see the actual wires) about 1/2 inch wide and about 6" long. That is the delay line. Look for small coils attached to both sides of that, and check it as well. With an ohm meter all those should be very low resistance, prob all less than a few ohms. Its under the chassis in about the middle under the chroma module.

You could also check the 3rd video amp transistor if it's socketed. they can be checked with a simple diode test. Let me know if you can find it (mounted on the top of the chassis, not part of a module).

If those things all check out,then I am out of sugestions, other than just going thru and checking resistors coils some of which can not be tested in circuit.

[ghjkl67]

I found the coil. It tested good. I couldn't find the other two smaller one's. The only thing attached to the larger coil was a small, round red part that I could not identify. It may have been the coil, but there was only one (it tested good as well). I also took out the 3rd video transistor. I don't know how to run a diode test, but I did find out that there is continuity with a little resistance between two of the three terminals. The other terminal seems to be standing alone. From what I know, I think the transistor is good.

[DaveWM]

use the diode test of a DMM. transistor is Emmiter Base Collector. the base is in the center. with a diode test clip check the EB then the CB one way it should read about .6v reverse the polarity of the leads and check again, it should be 0v
the polority of the leads will be different on NPN vs PNP type transistors, it does not really matter only that one way its .6 the other is 0

After check the EB and the CB check the EC, should be 0v reverse check again should be 0v.

You may find the voltage around .3v if so it just means its a germanium not silicon. Also this test is good for smaller signal transistors, large power transistors may not test the same.

all the testing must have the transistor out of the circuit, which is easy on the zenith if they are in sockets. Maker sure you put them back in the way they came out, the Emitter and Collector are not interchangeable.