Carbon composite in place of carbon film

[TinCanAlley]

Never mind the last post about the waveform. Seems it was generating that even after I disconnected the probe. I'm going to give it back to my brother and see if there is somewhere around here that rents them.

[DaveWM]

yep, with tvs you can only go so far with voltage readings, wave forms are were its at. put it back together and get some screen shots showing brigtness and the jail bars again.

Scopes are handy but expensive for a good one, you can get decent later models for around 100$ but you risk it not working, case in point my scope just took a dump on me so now I have to fix it.

[DaveWM]

You may just want to try your hand at fixing that scope, its prob pretty simple.

You do need to get a straight trace that reacts as it should.

[TinCanAlley]

Originally Posted by DaveWM

yep, with tvs you can only go so far with voltage readings, wave forms are were its at. put it back together and get some screen shots showing brigtness and the jail bars again.

Scopes are handy but expensive for a good one, you can get decent later models for around 100$ but you risk it not working, case in point my scope just took a dump on me so now I have to fix it.

Yeah, most of the scopes I've found listed for a decent price are either broken or untested (untested=broken most of the time). I can't really justify spending a decent amount on something I might use one or twice. I have a closet full of stuff like that already.

I'm attaching a pic of the jail bars and brightness. The brightness is greatly improved with much more available range, so that seems resolved. The jail bars, however, are still there and quite noticeable (even in lighter scenes). I've replaced the two 100K resistors, the 33K and the diode. None had any effect.

I have the scope's build instructions and I can go over it. If I'm not mistaken, this thing has tubes in it. I'll take them out and test them.

[TinCanAlley]

This scope has 10 tubes in it! Where to begin.

Well my brother built it, I'll have to enlist his help.

[DaveWM]

if the scope has not been recapped it may have issues there.

[DaveWM]

the fact that the horz convergence is not responding (I think that is what you said) and the horz blanking may be causing the jail bars sure points to a problem there. Is the width ok? not too wide?

[TinCanAlley]

Originally Posted by DaveWM

if the scope has not been recapped it may have issues there.

It's been recapped, but I don't know how long ago. I see a combination of electrolytic, film and those "orange drops" in it. I'm seeing my brother tomorrow, so I'll get more info on what's been done to it. He said it worked the last time he used it, but I didn't has how long ago that was.

[TinCanAlley]

Originally Posted by DaveWM

the fact that the horz convergence is not responding (I think that is what you said) and the horz blanking may be causing the jail bars sure points to a problem there. Is the width ok? not too wide?

The horizontal convergence for the blue moves quite a bit, but just not in line with the other colors on the sides. There is the coil and two pots that move around the blue, but no combination of them will get the lines where they should be on the sides without messing up the top and bottom horizontal lines (center convergence stays put).

I've gotten used to no overscan, so this set's image seems too wide. I believe, though, that the overscan is about 6%. I can just see the edge of the 5% line on the overscan pattern.

[jr_tech]

I may be missing something here, but why is the scope thought to be in need of repair... the waveform posted looks reasonable, and perhaps the 10 or so "ripples" at the bottom of the waveform might indeed correspond to the 10 or so bands "jail bars" seen across the TV screen?
jr

[TinCanAlley]

Originally Posted by jr_tech

I may be missing something here, but why is the scope thought to be in need of repair... the waveform posted looks reasonable, and perhaps the 10 or so "ripples" at the bottom of the waveform might indeed correspond to the 10 or so bands "jail bars" seen across the TV screen?
jr

If you scroll up to post #53 you'll see a waveform I posted. The waveform for the 170V in the pic is what supposed to be on the scope. I thought I had it, but that waveform didn't go away when I removed the probe. So it most likely isn't from the circuit, but from the scope itself.

I recalibrated the scope per manual and I was able to get both of those waveforms in the picture from the SM. However, all other attempts to scope out other points has given me garbage on the scope. I think there might be a short in the 10x probe.

[jr_tech]

Originally Posted by TinCanAlley

If you scroll up to post #53 you'll see a waveform I posted. The waveform for the 170V in the pic is what supposed to be on the scope. I thought I had it, but that waveform didn't go away when I removed the probe. So it most likely isn't from the circuit, but from the scope itself.

I really suspect that the probe could have been picking up the waveform without direct connection to the test point... a sensitive probe held near the horizontal section can easily do that. If you turn the TV off, does the waveform on the scope stop?
jr

[TinCanAlley]

I managed to get to good waveforms from the convergence section (easiest to get to and many test points). The forms matched almost completely. Then things went wrong. I think there's a problem with the 10x probe. It's a heathkit, so I'm going to take it apart and see what might be going wrong.

[DaveWM]

if you are getting good wave form the 170v pp then trace on through and see if you can see it getting to the base of the blanker

[TinCanAlley]

Originally Posted by DaveWM

if you are getting good wave form the 170v pp then trace on through and see if you can see it getting to the base of the blanker

I think the 10x probe is defective (it is 57 years old). I found it difficult to not only get the signal with it, but to keep it. Tapping it caused glitches. I looked over the schematics and it's pretty simple, but I don't like how the tip is designed. It's just a screw-in tip and the wire to it just hangs out the end of the probe and then the tip is attached. The wire just sit loosely in the tip, not soldered or attached in any way.

I've ordered a new probe and the BNC to banana plug converter. It should be here on Wed and I'll be able to get more done.