Are these things I should consider bad

[TinCanAlley]

Originally Posted by DaveWM

wow looks pretty good in the second pic, how does that look with regular content? can you adj for good contrast and reasonable brightness and not have jail bars? Now I wonder if there is a problem or are you just asking too much of it. Remember jail bar exist due to lack of complete blanking in retrace, if the CRT bias setups (contrast/brighness/G2) are pushed to an extreme I would not be surprised that they could show thru.

as far as were to hook up, I would pull the CRT socket back a tad and use the clip on style scope probe.

Thing is, the second picture is full contrast AND full brightness w/massive blooming. It's definitely being overdriven. If you try to watch program content, it is way too bright and washed out. The jail bars are the most noticeable with normal levels of brightness and contrast.

I usually bring up the contrast to the point of blooming and then back it off. I then keep backing it off until the level is right for the viewing environment. I then adjust brightness up until I get decent shading in the dark areas of the picture. Sometimes I have to go back and forth between the two controls to get it right. In no way am I driving it too hard with those controls and the G2 voltages are within range.

Tomorrow will be my day for checking the cathodes, G1 and G2s.

[TinCanAlley]

Originally Posted by sampson159

my magnavox bicentennial set has slight jailbars.only on a direct tv receiver.on my zenith converter and dvd player,no jailbars.at approx 50 percent brightness and contrast,no jailbars.these sets werent built for modern day receivers,etc.i adjust mine to a level where they are not noticeable or gone.purity is almost a non issue on your zenith.now post pics of screen with images!we want to see that glorious zenith picture.waited wayyyyyyy too long!

Is there a trick to taking pictures of the screen? The pictures always look bad compared to the live image.

[TinCanAlley]

Would it help if I were to video the scoping process tomorrow? I am going to scope all the cathodes, G1s and G2s and figured I'd record the process and then put it up on youtube. It'll be my first video upload.

I just thought that it might be more helpful for all involved if they got to see how I was doing it, how the scope was set and what the waveforms looked like.

[DaveWM]

Yes video would help IMHO.

[TinCanAlley]

Well the video didn't work out. It was too crazy trying to change the probe to different pins and change the scope settings all while trying to video. I would have spent longer editing the video than creating it. So I just went down the line and scoped the pins in order of color.

Below are the connections and the scope's volt/div setting. They all were with a time/div of 20us.

Green
Cathode .5V/Div
G1 20V/Div
G2 10V/Div

Red
G2 2V/Div
Cathode .5V/Div
G1 20V/Div

Blue
G2 2V/Div
Cathode .2V/Div
G1 20V/Div

When you look at the green G2 waveform, compare it to the red and blue G2s. The Green waveform came out nice and clean. The Red and blue, however, is a multiple form again. I don't know why this is happening, but the red and blue from should look the same as the green.

The attached pics will be in order of above (starting with Green Cathode). The first 6 will be in this post and the next 3 will be in the next post (seems only 6 can be attached per post).

Hope this helps. If it's true there shouldn't be any AC on the G1s and G2s, what's the deal?

[TinCanAlley]

Remaining pics from previous post.

[TinCanAlley]

So nothing? No ideas? Nothing about those waveforms brings anything to mind?

[old_tv_nut]

Did you move the scope probe ground lead during taking this series?
[Edit: you should connect the ground lead of the probe you are using to the chassis, keep it attached at one particular point for all the measurements, and do not connect any other scope ground leads to the chassis.]

The "fat" traces could be superimposed 60 Hz hum due to intermittent probe ground (can't tell from stills, but you could verify by slowing the scope sweep to vertical rate).

In any case, there appears to be ripple on the green cathode and grid, less on red and blue. Why they should be so different doesn't make a huge amount of sense, unless it varies with the scope probe grounding, because the bars you have shown pictures of appear to be monochrome - so they should be in all three guns.

Also, in the off-screen shots with a regular picture, the bars aren't visible. Are they visible to the eye at all with a regular picture, or only with a plain black scene?

[TinCanAlley]

Originally Posted by old_tv_nut

Did you move the scope probe ground lead during taking this series?
[Edit: you should connect the ground lead of the probe you are using to the chassis, keep it attached at one particular point for all the measurements, and do not connect any other scope ground leads to the chassis.]

The "fat" traces could be superimposed 60 Hz hum due to intermittent probe ground (can't tell from stills, but you could verify by slowing the scope sweep to vertical rate).

In any case, there appears to be ripple on the green cathode and grid, less on red and blue. Why they should be so different doesn't make a huge amount of sense, unless it varies with the scope probe grounding, because the bars you have shown pictures of appear to be monochrome - so they should be in all three guns.

Also, in the off-screen shots with a regular picture, the bars aren't visible. Are they visible to the eye at all with a regular picture, or only with a plain black scene?

The ground was connected to the same spot for all tests (I used the ground on the CRT socket). I will try to bring down the sweep rate and see if the waveform clears up.

The bars are most noticeable when the screen is darker like in a transition between scenes. You can see them with color screens, but only if the colors are light/pale.

I'm wondering if my 750V boost is working as designed. I haven't looked at it until today. So far all I did was check its voltage. It's 761VDC. I didn't check the AC as my DMM isn't a true RMS. I'll need to put it on the scope to see the AC. I figure I can start at the diode that steps it up and work my way to the G2 controls.

[jr_tech]

Originally Posted by TinCanAlley

I will try to bring down the sweep rate and see if the waveform clears up.

Possibly the "fat traces" are due to a very high frequency component riding on the waveform, so increasing the sweep speed might reveal its shape. Use the internal triggering of the 'scope to see if you can trigger on the superimposed (and presumably extraneous waveform) and display it to determine what it may be. So try both higher as well as lower sweep rates.
jr

[andy]

...

[TinCanAlley]

Originally Posted by andy

It's not unusual for the ground wire to act like an antenna and pick up signals from things like the flyback and yoke. It looks to me like you have ringing on all of those signals and voltages. It could be a filtering problem, but I think the ringing itself is the problem.

What voltages to you have on the 240v and 750v boost sources? If one of those is low, it could explain the lack of a bright service line, and be causing the bars.

These types of problems can be real head scratchers and often end up being the last thing you would suspect. It could even be the yoke or flyback. You might want to look for a parts donor in an ugly cabinet. A whole chassis transplant isn't a crazy idea if you value your time.

Those voltages test out as 248VDC and 761VDC. So their not on the low side.

I was hoping someone could look over the schematics I posted earlier and tell me what happens when the setup switch is activated. To me, a beginner, it looks like it does something and collapses the vertical. That's my best guess based on what I get looking over the schematics. If that's what's happening, then the lack of setup line for all but a faint blue is puzzling.

If it comes down to replacing the FB or yoke, I'll live with the bars. I don't want to get that involved. I think for the heck of it I'll look over all the caps and resistors in the 750V boost area. Could be a decoupling cap.

[zeno]

Originally Posted by TinCanAlley

Those voltages test out as 248VDC and 761VDC. So their not on the low side.

I was hoping someone could look over the schematics I posted earlier and tell me what happens when the setup switch is activated. To me, a beginner, it looks like it does something and collapses the vertical. That's my best guess based on what I get looking over the schematics. If that's what's happening, then the lack of setup line for all but a faint blue is puzzling.

If it comes down to replacing the FB or yoke, I'll live with the bars. I don't want to get that involved. I think for the heck of it I'll look over all the caps and resistors in the 750V boost area. Could be a decoupling cap.

Service switch kills vertical also kills video & gives the 3 video outs a
constant voltage. On this chassis it also adds a crude blanking pulse.
If all the DC voltages are correct you should get very bright service
lines. At that point its 99% the CRT. Sometimes the CRT can look
& test good but be a little weak.
Good news ! Since I was a bench man & only did about 25 of these
sets I ran it by our old road man over a beer. He did a repair on
one once & it had the exact same jailbars. Bad news is the set was
very old & they didnt want to pay to pull the chassis. At least you
know this wasnt self induced & a real failure, possably common.
Just for kicks remove the wire from service switch that go to
jcn of R295 & R297. See if they go away.

73 Zeno

[DaveWM]

you thinking a leaky switch Zeno?

[zeno]

Originally Posted by DaveWM

you thinking a leaky switch Zeno?

A long shot but yes. When in service instead of video they tie in
a pulse from the FBT. Zeniths had problems with the tiny
remote/man SW & on/off buttons on this vintage getting leaky
& causing random on/off. Rare but they can get leaky & its
gonna be something strange if ever found.

I wonder if anyone here is on the old Electronix pay site ? I bet
the answers there..........

73 Zeno