Are these things I should consider bad - Page 10 - Videokarma.org TV - Video

TinCanAlley · #**136** 10-03-2013, 05:17 PM

Quote:

Originally Posted by Username1

I know its trying to be taken in different directions by different people with ideas about what can be wrong. I'm quite surprised you have not called us all a bunch of nuts by now and thrown that tv off the roof and went and got another off CL for free or $10. and just said the hell with it...... : )

If its not right in that area of the coupling transformer, that diode, open resistor, then it's got to be the pink fairy inside the flyback, she probably can't get any air cause of that extra silicone on it.....

I know it's a Letterman thing, but you may be able to plead your case to Lenno, he's on your coast, maybe he'll make an exception and do a Letterman and toss it off a roof for you and put it on national tv..... Could be the best solution to the problem...

I've spent years looking for this set. I'll either fix the jail bars or learn to live with them.

TinCanAlley · #**137** 10-03-2013, 07:24 PM

Okay, she's got the new damper diode and the 1.5ohm resistor. The resistor tested as 1.8 and the one I replaced it with was dead on 1.5.

I also tested the resistance of the coupler transformer and one side was pretty much dead on at .23ohm (Sams has .25) and the other side was 92ohm (Sams has it at 100ohm).

She's been running for a little bit now and nothing blew up. The jail bars are still there, though. Not sure where to go next.

Username1 · #**138** 10-03-2013, 07:33 PM

I'm not too sure what to think of next either....

Well, you know about now, I would be taking a small cap and jumping those caps after the collector of the HOT with the set on and watching the screen to see what it does.... Not recommended, But if you ran across a spot that made a change in those jail bars, it might be worth it....

Do you think anyone ever removed a metal shield from somewhere and never put it back ?

I really don't think its in the yoke, so it's probably a bad yoke....

TinCanAlley · #**139** 10-03-2013, 08:49 PM

Quote:

Originally Posted by Username1

I'm not too sure what to think of next either....

Well, you know about now, I would be taking a small cap and jumping those caps after the collector of the HOT with the set on and watching the screen to see what it does.... Not recommended, But if you ran across a spot that made a change in those jail bars, it might be worth it....

Do you think anyone ever removed a metal shield from somewhere and never put it back ?

I really don't think its in the yoke, so it's probably a bad yoke....

Those caps after the HOT are all the safety caps. They're all new.

All the shields seemed to be in place when I got it. The only one removed was when I put in a new, updated, subcarrier regen module. It was redesigned with a small shield on it to protect from interference. The last person to adjust the APC stripped the plastic slot in the pot and then pushed it so hard they broke it free from the solder joint. The jail bars were there with the old and still there with the new, so I'm sure it's not the shielding.

DaveWM · #**140** 10-04-2013, 09:42 AM

Perhaps this has been asked and answered but will bring it up.

I presume the jail bars are caused by either of the below:

video info (lack of blanking during retrace)

video info (ringing happening during trace)

non linear sweep during trace (not likely) if this was the case I would think holding the scope prob near the horz leads of the yoke should give a wave pattern that would have the ringing during the rise time, but that is just a guess.

Did you ever try putting on a blanked out screen and scoping the G1's (and may was well look at the cathodes and G2 for that matter, even though they should not have video info).

with an blanked out screen you should have no AC signal at the G1 (or cathodes and G2 for that matter).

You should adjust the brightness and contrast on the blank screen to make the jail bars as bad as possible.

This should be done with a blank screen image being fed to the tuner so you can see the horz sync pulse (the blanking period) followed by a burst pulse.

If there in no AC signal between H sync pulses, then is seems it would HAVE to be insufficent blanking during retrace.

If that's the case I would still be hung up on how you have the brightness/contrast/screen drives setup. I think this is the same set that you said you could not get the CRT setup done when using the described SAMs method using the setup switch and G2 adjustments.

TinCanAlley · #**141** 10-04-2013, 11:00 AM

Quote:

Originally Posted by DaveWM

Perhaps this has been asked and answered but will bring it up.

I presume the jail bars are caused by either of the below:

video info (lack of blanking during retrace)

video info (ringing happening during trace)

non linear sweep during trace (not likely) if this was the case I would think holding the scope prob near the horz leads of the yoke should give a wave pattern that would have the ringing during the rise time, but that is just a guess.

Did you ever try putting on a blanked out screen and scoping the G1's (and may was well look at the cathodes and G2 for that matter, even though they should not have video info).

with an blanked out screen you should have no AC signal at the G1 (or cathodes and G2 for that matter).

You should adjust the brightness and contrast on the blank screen to make the jail bars as bad as possible.

This should be done with a blank screen image being fed to the tuner so you can see the horz sync pulse (the blanking period) followed by a burst pulse.

If there in no AC signal between H sync pulses, then is seems it would HAVE to be insufficent blanking during retrace.

If that's the case I would still be hung up on how you have the brightness/contrast/screen drives setup. I think this is the same set that you said you could not get the CRT setup done when using the described SAMs method using the setup switch and G2 adjustments.

You are correct. I am unable to get any drive other than blue to produce a faint line in setup. The other two don't show up at all. Well, they might if I could completely black out my room (guess I could try it at night). Still, if the line doesn't show up in a dim room, that not normal, right?

I had to pull the IF and adjust the G2s for a dim raster. Checking the voltages, they are within the range noted by Sams.

My new pattern generator allows me to pretty much blank everything out and just leave the jail bars (IQW off, chroma off and luminance off).

So I should pull the socket back a bit, put the probe's j-hook on each of the G1s and the cathodes. My scope is not designed for the voltage found on the G2s and I don't have a HV probe.

As for the ringing around the yoke, I see a ringing type pattern in that whole area, especially the focus wire (just having the probe near, not touching). I don't know if it's actual ringing or just a normal electrical field the scope is picking up. I'm attaching a pic of what the scope sees in the general HV area and around the yoke wires, focus wire and FB.

DaveWM · #**142** 10-04-2013, 12:26 PM

the G2 is prob around 800v max, at 10x and if you have a 10v setting on the scope you should be able to read it, besides you will have the scope on AC so it should not matter. Start with 10x 10v then AC and then switch to lower and lower voltage settings on scope, that covers the G2, but there really should be no AC here anyway. Same goes for the cathodes.

G1 is where the video signal shows up (luma and chroma on this set) again start with 10x on 10v AC and work down the voltage, looking for a wave form pattern between Horz blanking pulses, the dark screen should be still a fair amount below the max amplitude found on the horz blanking pulse.

Generally speaking the horz video pulse should blank out the signal during flyback time, it is aided by the pulse from the fly that is fed to that blanking transistor (talking horz now) to furter cut off the CRT.

Zeno, any possibility this could be an AGC issue? maybe limiting the blacker that black region?

Tin Can give us a good shot of the CRT with the jail bars again with a transmitted blank screen. Adj the contrast and brightness to max and min the effect, then lets see some actual images using those same max and min settings.

the question that needs to be figured is
jail bars in video or sweep.

the below I really don't think is the issue, I still want to think its a blanking issue, not enough cut off to the CRT during flyback) but here it is:
as far as the horz sweep, you want to look at the rise time not the ringing after the drop off (that is a given and will always be there to some extent).

can you see the horz rise by holding the prob right up near one of the horz defection coil leads? if so look at the rise, is in smooth or rippled, the ringing you are showing in that other pic is I presume the ringing after the sudden drop off, not during the trace part of the scan. You want to see if the trace part is smooth.

andy · #**143** 10-04-2013, 03:34 PM

...

TinCanAlley · #**144** 10-04-2013, 03:39 PM

Quote:

Originally Posted by DaveWM

the G2 is prob around 800v max, at 10x and if you have a 10v setting on the scope you should be able to read it, besides you will have the scope on AC so it should not matter. Start with 10x 10v then AC and then switch to lower and lower voltage settings on scope, that covers the G2, but there really should be no AC here anyway. Same goes for the cathodes.

G1 is where the video signal shows up (luma and chroma on this set) again start with 10x on 10v AC and work down the voltage, looking for a wave form pattern between Horz blanking pulses, the dark screen should be still a fair amount below the max amplitude found on the horz blanking pulse.

Generally speaking the horz video pulse should blank out the signal during flyback time, it is aided by the pulse from the fly that is fed to that blanking transistor (talking horz now) to furter cut off the CRT.

Zeno, any possibility this could be an AGC issue? maybe limiting the blacker that black region?

Tin Can give us a good shot of the CRT with the jail bars again with a transmitted blank screen. Adj the contrast and brightness to max and min the effect, then lets see some actual images using those same max and min settings.

the question that needs to be figured is
jail bars in video or sweep.

the below I really don't think is the issue, I still want to think its a blanking issue, not enough cut off to the CRT during flyback) but here it is:
as far as the horz sweep, you want to look at the rise time not the ringing after the drop off (that is a given and will always be there to some extent).

can you see the horz rise by holding the prob right up near one of the horz defection coil leads? if so look at the rise, is in smooth or rippled, the ringing you are showing in that other pic is I presume the ringing after the sudden drop off, not during the trace part of the scan. You want to see if the trace part is smooth.

Okay, give me about an hour and I'll provide the images you requested.

Also, the max voltage on mine is 5V/div. The manual says it +/- 250V DC plus peak AC at 20Kilohertz. I don't think I should go near the G2s, do you?

DaveWM · #**145** 10-04-2013, 05:01 PM

Quote:

Originally Posted by andy

I think you meant to say that the cathodes are where the video signal is applied to the CRT. G1, and G2 should have DC on them.

oops right thanks Andy.

Tin Can just do the check on the cathodes with the scope for now with the transmitted blank screen, use the horz rate, AC, make sure you can see the entire trace including two horz sync pulses.

after that the G1 and the G2, If you scope works like mine the AC setting should allow you to look at the G2 (using 10x and 5v would be 50v per div) since it should see very little AC at all, assuming the filter caps are ok on those supplies (the 250 and the 870, both derived in the horz circuit). If you want you could start by turning the screen pots fully CCW that would place the G2 at the lowest DC voltage of 250v (but again it should not matter as there should be NO ac anyway).

TinCanAlley · #**146** 10-04-2013, 06:04 PM

Quote:

Originally Posted by DaveWM

oops right thanks Andy.

Tin Can just do the check on the cathodes with the scope for now with the transmitted blank screen, use the horz rate, AC, make sure you can see the entire trace including two horz sync pulses.

after that the G1 and the G2, If you scope works like mine the AC setting should allow you to look at the G2 (using 10x and 5v would be 50v per div) since it should see very little AC at all, assuming the filter caps are ok on those supplies (the 250 and the 870, both derived in the horz circuit). If you want you could start by turning the screen pots fully CCW that would place the G2 at the lowest DC voltage of 250v (but again it should not matter as there should be NO ac anyway).

Okay, I know the G2s are in the bottom right of this schematic and feed the higher voltage (540 - 640V) pins on the CRT. Are the G1s the ones in the 140V range and the cathodes in the 36V range? If so, should I test at the pins of the CRT or find a spot on the chassis?

You'll also note the test points on the schematic that feed the taps, etc. Are those ones I should scope? And if so, do they take the place of doing so on the CRT pins for those?

TinCanAlley · #**147** 10-04-2013, 06:28 PM

Here are a few pics. First one is contrast down and brightness up. Second is brightness and contrast up. Third is a question as to whether I need to redo purity of if it needs a good degauss.

DaveWM · #**148** 10-04-2013, 07:35 PM

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.

DaveWM · #**149** 10-04-2013, 07:36 PM

you have a very slight purity issue, I would leave it alone as rarely will you notice that with regular viewing.

sampson159 · #**150** 10-04-2013, 07:49 PM

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!