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  #46  
Old 09-30-2013, 09:15 AM
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Quote:
Originally Posted by TinCanAlley View Post
So the flat line I see is correct. About the only thing I can do is move the coupler to GND, move the trace line to the bottom of screen, set the voltage/div, move the coupler to DC and then measure voltage after the trace line moves up. That's okay with me.

If I see ringing on the base of a transistor, do I look at the collector to see if the ringing has been amplified? Also, I seem to recall someone suggesting I ground the base of the ABL transistor to see if the jail bars go away. The voltage on the base is under 1V, so is it okay to ground it? Doing so won't short anything out?
Ringing may or may not be amplified, depends on circuit.
Grounding the ABL base will kill the ABL. If the jailbars are getting
in there they will go away. You may or may not see other changes
without ABL.
B+ lines should be clean, sometimes there is a very small amount
of hash but nothing like 5% or 10% of voltage.
With this problem you have to take things in order.
1) be sure all B+ are clean & correct
2) scope starting with the detected video from IF strip pin 5
3) work your way to the right through video til the
waveform goes "bad" thats where it gets in.

73 Zeno
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  #47  
Old 09-30-2013, 10:39 AM
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Last edited by andy; 12-05-2021 at 07:52 PM.
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  #48  
Old 09-30-2013, 10:58 AM
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Quote:
Originally Posted by zeno View Post
Ringing may or may not be amplified, depends on circuit.
Grounding the ABL base will kill the ABL. If the jailbars are getting
in there they will go away. You may or may not see other changes
without ABL.
B+ lines should be clean, sometimes there is a very small amount
of hash but nothing like 5% or 10% of voltage.
With this problem you have to take things in order.
1) be sure all B+ are clean & correct
2) scope starting with the detected video from IF strip pin 5
3) work your way to the right through video til the
waveform goes "bad" thats where it gets in.

73 Zeno
When you say the IF strip pin 5, do you mean the one labeled "C1"? I'll post an pic of the waveform I get from the B+. It's unlike any other waveform I get. It is similar to the ringing on the ABL base, but it is a multiple waveform of about 5 or more like you're on acid and tipping. It also expands and contracts from about three to 5 or more. It's only on the B+ that I get more than a single line waveform.

I've traced the B+ to two different sources. One is from a line from the transformer that is amplified by a diode and then is tapped into the canister. From there it goes to the chroma module and makes it way around the boards. The other B+ comes from another line of the transformer and goes though a resistor and then on to the horizontal board where it connects to the pin right next to where the first B+ connects. It's a loop, but why from different lead of the transformer and why is only one end filtered by the caps?

When I get home I'll take a picture of the waveform I mentioned and post it.
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  #49  
Old 09-30-2013, 11:00 AM
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Quote:
Originally Posted by andy View Post
You're still better off sticking to X10 unless you're at the lowest v/div setting and still can't see the signal because it's too weak. An X1 probe will tend to load down any signals you're looking at.
I'll do that. Guess I misunderstood the need for the 10x. Most of what I read and watch talked about sensitive modern circuits needing the probe. For some reason I don't think of an older television as being that sensitive with all the high voltage and other things going.
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  #50  
Old 09-30-2013, 01:09 PM
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Okay, here are recent waveforms.

First pic is the ABL base. It measure roughly .75 volts DC and this waveform is the AC with settings of 1 volt/div and 20us time/div. Odd thing is, the AC and DC waveforms are identical.

Second pic is the ABL collector's DC waveform. It measured roughly .5 volts DC. The AC looked the same but with settings of 20m volt/div and 20us time/div.

The third pic is the B+ 125V with a setting of .5 volt/div, but with the 10x probe the display is 5 volt/div and 5ms time/div. See how fat it is? Every other wave form is a single line except for the B+ 125.

Last pic is the B+ 125V again with different settings of 1 volt/div but with the 10x probe the display is 10 volt/div and 10us time/div. The DC showed a flat line at 50 volt/div for roughly 2.5 divisions.
Attached Images
File Type: jpg ABL Base AC.jpg (51.7 KB, 6 views)
File Type: jpg ABL Collector DC.jpg (53.2 KB, 6 views)
File Type: jpg B+ 5ms scan.jpg (44.5 KB, 7 views)
File Type: jpg B+ 10us Scanrate.jpg (38.2 KB, 8 views)
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Last edited by TinCanAlley; 09-30-2013 at 02:50 PM.
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  #51  
Old 09-30-2013, 01:40 PM
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Quote:
Originally Posted by TinCanAlley View Post
Okay, here are recent waveforms. The B+ measurements were done with a 10x probe, so the volt/div are actually 10x lower.
I'm not sure that I understand your use of the term "lower" in this case... For example, if the scope knob is set for 10V/div and you use the 10x probe, is the waveform measurement on the scope now? :

a) 1V/div
b) 100V/div

jr
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  #52  
Old 09-30-2013, 02:23 PM
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Quote:
Originally Posted by jr_tech View Post
I'm not sure that I understand your use of the term "lower" in this case... For example, if the scope knob is set for 10V/div and you use the 10x probe, is the waveform measurement on the scope now? :

a) 1V/div
b) 100V/div

jr
With the probe in the 10x mode it would be 10 volt / div. Isn't that how it works? If I set the scope to 1 volts/div and put the probe in 10x mode, it would reduce/lower/attenuate it by a factor of 10 and the display should be read as 10 volt/div?
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  #53  
Old 09-30-2013, 02:40 PM
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Okay, just grounded the ABL's base leg and the jail bars remained. The only affect it had was to brighten the screen when grounded and go back to original brightness when ungrounded. So it seems the ABL circuit isn't to blame.
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  #54  
Old 09-30-2013, 02:52 PM
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Quote:
Originally Posted by TinCanAlley View Post
If I set the scope to 1 volts/div and put the probe in 10x mode, it would reduce/lower/attenuate it by a factor of 10 and the display should be read as 10 volt/div?
That is correct, the "10x" is the *attenuation* factor, not a multiplier. It was not clear that you were reporting the actual voltages of the circuit or the amplitude seen on the scope, with or without taking into account the 10x *attenuation* of the probe, or worse still using the "10x" as a multiplier.
So "b" is the correct answer to my question... agree?

Now, where do you set the baseline "0 volts" before probing a DC voltage? If probing a positive voltage, I set the baseline to the lowest line on the 'scope face and count divisions up from there after the DC is applied to the probe. If unsure of polarity, I set the baseline (with no voltage applied) to the center graticule line and see which way the trace goes when probing the voltage.

jr
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  #55  
Old 09-30-2013, 02:58 PM
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Quote:
Originally Posted by jr_tech View Post
That is correct, the "10x" is the *attenuation* factor, not a multiplier. It was not clear that you were reporting the actual voltages of the circuit or the amplitude seen on the scope, with or without taking into account the 10x *attenuation* of the probe, or worse still using the "10x" as a multiplier.
So "b" is the correct answer to my question... agree?

Now, where do you set the baseline "0 volts" before probing a DC voltage? If probing a positive voltage, I set the baseline to the lowest line on the 'scope face and count divisions up from there after the DC is applied to the probe. If unsure of polarity, I set the baseline (with no voltage applied) to the center graticule line and see which way the trace goes when probing the voltage.

jr
Yes, if the dial is set to 10 and the probe is on 10, then the display is 100 per division. I edited my original post to reflect the probe and dial setting.

For the DC I put set it to GND and moved the trace to the bottom of the screen and then switched to DC. It moved up as it was positive. Since the DC was showing a waveform, I moved the baseline to the top of the first division so it would show the entire waveform.
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  #56  
Old 09-30-2013, 03:20 PM
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Originally Posted by TinCanAlley View Post
Since the DC was showing a waveform, I moved the baseline to the top of the first division so it would show the entire waveform.
Ahhhh! that's where you lost me... the reported values did not *seem" to correlate to what I was seeing on the 'scope.
jr
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  #57  
Old 09-30-2013, 03:44 PM
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Originally Posted by jr_tech View Post
Ahhhh! that's where you lost me... the reported values did not *seem" to correlate to what I was seeing on the 'scope.
jr
My biggest issue is why the B+ waveform is so fat. I found that if I adjusted the trigger level I could thin it out, but then it would lose the trigger. To get it back I had to zero out the trigger level, but then I got the fat waveform.

I just scoped all of the B+ 125V to and from each of the modules. It was consistent throughout, if I thinned out the waveform, it was roughly 1 VPP before it lost the trigger. If you count the fat wavefrom, it would be roughly 3.5 VPP.

So I'm pretty sure 1 VPP of ringing isn't going to create the jail bars. That and I've pretty much ruled out the ABL.

Not sure where check next. I've done the horizontal oscillator, wave generator and output on the horizontal board. I don't have the probe necessary to do anything with the FB, yoke or HOT.
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  #58  
Old 09-30-2013, 04:05 PM
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Without knowing the specs. for the 125V supply, it would *seem* to me that 3.5 volts of garbage would be more than I would like to see. Perhaps there are some filter caps in the 125V supply that are not functioning properly.
jr
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  #59  
Old 09-30-2013, 04:11 PM
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Yes C-1 is Zeniths term for composite video. Some sets
even have a "C-1 adjust" pot.
Grounding the ABL base proves its NOT coming from there so ignore
all between the ABL base & tripler.

Depending on the scope I was using I almost never used
DC only AC since I was looking at waveforms. On my sencore
there was a built in meter to speed things up.
Also be sure all your calibrations are set. The are the red
knobs are set to "cal". Some have an arrow to show which direction
to turn them.
If the scope is dual trace you can use sync on B to stablize the
waveform. Hook the B channel probe to a clean hoz signal
such as the hoz drive collector, this may get rid of the multiple
traces.

73 Zeno
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  #60  
Old 09-30-2013, 04:17 PM
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Okay, moved on the 240V boost section. I'm attaching three waveforms. Each are done at 50V/div and 20us/div.

The first is directly from the lead off the flyback where it connects to the boost diode. It's taller than my scope can display. I didn't realize it was 900V. Glad my scope didn't do something bad. I'm growing fond of it.

The second is on the other side of the boost diode and is now 248V. The waveform covers just over two divisions, so it's just over 100V and there's ringing in it.

The third is through a resistor and to the 10uf 300V capacitor. Again, I'm getting a really crappy waveform, but the basic form is the same as pic 2.

Now I tried scoping the other 240V boost, but I couldn't get a meaningful waveform. Where I scoped for pic two, it splits off from there to another point where it's connected to a 15ohm coil. It measures at 248V, but the waveform is pretty much non-existent. Don't know if it's the coil smoothing it out, or if my settings aren't working for it.
Attached Images
File Type: jpg B+ 240V (1) Small.jpg (37.8 KB, 5 views)
File Type: jpg B+ 240V (9) Small.jpg (32.3 KB, 4 views)
File Type: jpg B+ 240V (5) Small.jpg (39.3 KB, 3 views)
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