Tuning up a 1988 Zenith System 3 that I found.

[MRX37]

Now that I actually have a camera capable of taking clear shots of small text, maybe these images will help identify just what kind of Zenith I have here:





So far I've replaced the one lytic cap on the CRT neck board (10uf, measured at 7.6uf). I also replaced the main filter cap (a 680uf@200 volt cap, replaced it with a slightly smaller 680uf@250 volt cap.) And I replaced a 33uf@200 volt cap that's near a heatsink. It tested fine, but judging from the label, it's seen some heat. I replaced these caps mainly because after 20 years of use, they're probably ready to be retired. These cap changes haven't affected the following problems:

I still have a few small issues with this TV. I've occasionally noticed that there's a sort of stripe on the left side of the screen that's a bit brighter then the rest of the picture. It only appears in some scenes though. Also, when watching a letterboxed program, the black borders will become brighter when the scene is bright. That makes adjusting the black levels hellish, as I use those black borders to set the brightness/contrast. The picture also changes size depending on how bright or dim it is. I'd guess that this is normal.

Also, I've noticed that the audio kinda crackles and pops when a loud sound is playing. Most noticable in videogames. the speakers appear to be fine though, because I can turn the volume up and it sounds fine, but if the sound is loud, it crackles regardless of how low or high the volume is.

This TV is unique to me. It's unique because it works, but I can't really sell it. Picture's still pretty good overall. CRT seems to have some life left in it. The electronic keypad on the front is damaged. Cosmetic damage, it still works fine. However this damage makes this TV unsellable. This is fine with me as I wouldn't mind a TV in my bedroom that's cable ready and works with a universal remote... I'd like to whip this Zenith into shape if I can.

[zenith2134]

Sounds like it's off to a good start. The 'stripe' you speak of could be two things. First, if the purity is off there could be a permanent stripe on one side of the picture. Second, there is probably a small capacitor in the video supply circuit which has gone down in value. Very common.

If you wanna whip it into shape, of course set the greyscale and focus, clean the crt neckpins with DeOxit, and make sure to reseat all of the module pin-connectors/clean with deoxit. These can cause a hell of a lot of intermittent issues.

One more tip that I like: Run the set with the brightness, color, and contrast at maximum (tint at half) for 20 minutes. This supposedly cleans residue off of the electron guns allowing them to work better.

[MRX37]

I don't believe the stripe is a purity issue. The color is not affected, just the brightness.

Also, where the hell is the video supply circuit? Is it on the main chassis board?

I'm not too worried about the electron guns. Sure the CRT's seen some hours, but it's got life left in it.

[zenith2134]

Not too familiar with that model, but I'd look for dried caps (near heat) on the 9-770 and the video output board. The 9-728 has the color decoding and matrix stuff, not too sure if there are any drive voltages derived there.

As for the guns, even on a crt that tests 110%, you can improve overall focus and color tracking by performing this procedure. Really nothing to lose IMO.

[MRX37]

Well, I'll worry about the guns after I solve the stripe, and the audio popping issue.

PS: One thing I forgot to mention: The replacement 680uf cap I put in is only rated for 85 degrees Celsius. the original was rated for 105 degrees Celsius. I don't *think* this will be an issue, as that cap isn't next to anything that gets hot, and the old cap's label didn't shrink any, which I'm sure it would have done if it actually got up to 85 degrees Celsius.

[zenith2134]

Using an 85C cap in a circuit that calls for 105C is counterproductive IMO. Sure, it'll be fine for awhile but its just bad practice. That said, in this TV it really doesn't matter. With quality audio gear or a very collectible set I wouldn't do it though.

Forgot to chime in about the audio popping issue. I'm not sure what you mean. Does the output simply clip on peaks? (more prevalent in video games and DVD since they have more range than most broadcasts)

If its more of a crackle sound, its likely a bad connection or dying electrolytic filters.

[MRX37]

Of course I'm not going to use an 85C cap in an area that actually gets hot, but in this case I had a couple 680uf caps from a 2003 Sony TV, they're rated for 50 volts higher then the old cap was, and while slightly smaller, the leads fit just fine. I consider the smaller size an advantage too, more air space around it.

The audio issue is weird. It's only showed up in video games so far, and shows up on loud sounds. This is the only TV that's done this with that game system, and that RF modulator.

[zenith2134]

Hmm, thats a headscratcher. Maybe the AGC control needs adjusting. Since you're running composite video through a modulator, the signal may be too 'hot' for the RF section of the Zenith. Worth a try...

[MRX37]

Originally Posted by zenith2134

Hmm, thats a headscratcher. Maybe the AGC control needs adjusting. Since you're running composite video through a modulator, the signal may be too 'hot' for the RF section of the Zenith. Worth a try...

Could I test that by attenuating the signal, say by running it through 100 feet of cable?

Still, the left side of the screen sometimes being brighter is more of a concern. is the video module on the main board itself, or seperate from the main board?

i'll snap a pic of the inside of the TV if it'll help.

[zenith2134]

The 9-728 board and the 9-466 board are where you wanna be looking, as far as the video problem. Again, make sure to unsnap and reinstall ALL of those module connectors. If possible spray em all with cleaner or use an old toothbrush and isopropyl. This is standard practice whenever I open up an 80s Zenith.

You could try spooling up some coax cable to see if it attenuates the signal a lot, but IMO it'll take a heck of a lot to do so. Depends on the cable's resistance/inductance etc.

Quick and dirty test: unplug the F- connector from the set and hold it very close to the port, aor hanging out of the port, to get a snowy picture. This should help you decide if something's getting overloaded.

[MRX37]

I'm going to work on this TV somemore tonight when I have the time. In the meantime, here's a pic of the brighter stripe I was talking about:


You can really see it in the black border in the top left corner of the screen. This brighter area is only sometimes there. It may depend on how bright the scene is, I'm not sure.

[zenith2134]

Based on the pic, I'd say it's the video caps for sure. If you notice, the black level isn't uniform on the left side of the screen, from top to bottom.

Check the main filter caps and the supply going to the video output board. If the video output transistors aren't getting a steady supply (dried up filter caps) this can happen.

[RobtWB]

About a year and a half ago I picked up a SE2023W set at an estate sale. It dates to September 1988. The reasons I brought it home were that it was obviously a low hour set, and it had the original rabbitt ears and bowtie still wrapped in the original packaging sticking on top of the set. The case was also flawless. No scratches, dings, dents, fingerprints etc. IIRC I paid a whole 25$ for the set.

The set has the Zenith hallmark of incredible color saturation.

Like my 1991 Panasonic 19 inch tabletop set, a simple elagant set of a quality no longer produced anywhere.

For a 20 year old set I was amazed that the set still produced such a fine picture. I was sure that I would have seen signs of aging components with this set, but not so.

I used the set with rabbitt ears as a bedroom set for a while, but now it resides in the utility room, in storage with a bunch of other sets.

[zenith2134]

Well I got an '89 the other day and it does work but the crt is aging rapidly. I don't think it will last much longer, but judging from the inside this one saw a TON of use.

[MRX37]

Here's a picture of what this bastard looks like inside.


Can anyone here tell me where the video output boiard is from this pic? is it on the main board or is it one of the modules?

Too many wires... and many of them have connectors that look alike. Thank god I have enough sense to mark similar looking connectors with a Sharpie so I can tell what goes where.