Zenith 14DC16 Colour question/problem

[maxhifi]

Hi All, new forum member here.

I have a Zenith 14DC16 portable hybrid TV set with single button space commander remote control. Have had it since 1994, when I picked it up for free. I have used it fairly sparingly over that time, and the only repair it has required, has been a replacement of both tubes in the VHF tuner.

I have the sams package for the set, and basic knowledge about how TVs work. Audio/radio have been hobbies of mine for years, but I have only done minor repair work on TVs.

In general the set is in excellent working order - the picture is sharp and free of noise, and the picture geometry is more than decent for such an old TV. The picture is bright, and when the image is a solid colour, it is consistent over the entire screen area.

Question is as follows... when watching certain shows, especially The Simpsons, it's extremely hard to get the tint to stay the same over the course of a show. In one scene, they look yellow, then the next a bit green, and in another a bit orange. In all cases I can adjust it to the right colour using the tint control, but then later on it will be different. Not all programs seem to show this effect, but when it is happening it is really annoying, and detracts from the otherwise perfect operation of the set.

I am targeting the 3EJ7 burst amplifier, and the 9MN8 G-Y, R-Y, B-Y amplifier as possible culprits. If either of these tubes are weak, or operating in some non-linear region, I can see how this would upset the colour. I have no tubes to use as substitutes, so thought I'd see if I could get a second opinion before I start ordring parts. There appears to be no electrolytic capacitors in the colour circuitry, and I am really at a loss as to what else it could be.

Any input from someone experienced with TVs of this era would be greatly appreciated.