Tuning up a 1988 Zenith System 3 that I found.

[radiotvnut]

Originally Posted by 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.

The video output board is the module that plugs into the CRT neck. I know what you mean about those wires. They are usually marked; but, not very well. And, they make it very hard to pull the chassis for service with everything connected.

[MRX37]

Well hell, I've already changed the one bad lytic cap on the CRT neck board. What else would be causing the uneven black level?

[roundscreen]

Originally Posted by MRX37

Well hell, I've already changed the one bad lytic cap on the CRT neck board. What else would be causing the uneven black level?

Look for a 4.7 or 10 uf cap @ 250 v cap near the fly back transformer. That set has a scan power supply and the power for the video comes from the flyback transformer. If you do not see one there look for the same value caps on the crt board itself.
Ed

[MRX37]

There is only one electrolytic cap on the CRT neck board, a 10uf@50 volt, which I've already replaced.

I did replace one 33uf@200 volt cap near the flyback. It tested good, but it's seen some heat.

Okay, I'll focus on the caps around the flyback when I get time to mess with it again.

[MRX37]

There are only three electrolytic caps near the flyback, and they all test fine. Any other ideas as to what's causing the uneven black level?

(No, it's not phosphor burn in.)

[wa2ise]

Weak (dried out) caps anywhere in the video signal path will do that. Even the small ones, like 10uF coupling caps.

[MRX37]

Originally Posted by wa2ise

Weak (dried out) caps anywhere in the video signal path will do that. Even the small ones, like 10uF coupling caps.

So, I go back to my initial question. Where do I look for these caps? On the main board, on a seperate module? There's probably 500 lytic caps in this TV, and going through and testing each and every one is frankly not worth the trouble.

[MRX37]

Okay, an update for you all:

After setting this TV aside for awhile, I went back and replaced a 33uf@200 volt cap that tested good, but was a bit on the low side. This might have solved my uneven black level, but I can't be sure, as now the brightness seems to be fluxuating, like maybe the brightness knob is dirty. When i first powered it up after installing the new cap, the G2 was up so high that retrace lines appeared. I lowered the G2, but the picture's brightness still seems to be fluxuating.

I'm going to clean the front panel controls later, but I'm wondering if the flyback G2 control is also dirty and whether or not it's safe to squirt anything into it.

[radiotvnut]

See if there is a screwdrived adjustment hold near the customer controls marked "BR". This is the brightness range control and may need to be turned down a little. I had a Zenith come in awhile back where someone had maxed out the control and it was very bright and flickering.

[MRX37]

Okay, figure out this one if you can:

My flickering brightness only happens when the TV first powers up, and only AFTER it's been unplugged for awhile.

This TV always showed retrace lines when it was first turned on after being plugged in, and these always go away in a few seconds. This flickering brightness also goes away after a few seconds, and won't return unless I unplug the TV and let it sit for a bit then plug it back in and power it up.

If it's nothing serious, then I won't worry about it, as the uneven black level issue seems to be fixed now.

EDIT: NOPE! the uneven black level is still there. But after the Tv running for a bit, the brightness flickered again and the black level is even right now. I don't get it...