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  #16  
Old 09-27-2013, 08:45 PM
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Quote:
Originally Posted by andy View Post
Have you tried scoping the CRT cathodes to see if the ringing is there? This will tell you if the problem is getting in through the video chain.

I would also try placing the scope probe tip near (NOT TOUCHING) the case of the HOT to see if there is any ringing on the signal you will pick up. Try the same thing near the yoke, and yoke wires. You will need to use a low volts/div setting, but you should be able to pick up radiation of the horizontal sweep signals. Don't try to measure them directly since the high voltages pulses will damage the probe, or scope.

Your problem could be caused by the flyback, or yoke oscillating. This seems likely to me since the bars are clearly synchronized to the horizontal sweep, and you seem to be seeing it everywhere that has pulses from the flyback.

Finally, can you remember if it had the problem when you first got it (before you did anything to it). I seem to remember that you didn't mention it until you had done a lot of cap replacement.
Okay, I scoped the HOT by placing the plastic safety tip against the shell. That's the fist pic and I see no ringing. The second pic is the focus wire and I'm assuming that's ringing on it, but I don't know if that can create the bars. Also, with the probe touching the yoke wires, I get roughly the same as the focus, but it shows less ringing the closer I get to the wires. So I'm not sure if it's really ringing or just that the probe is picking up interference.

So what would you suggest next?
Attached Images
File Type: jpg Hot Small.jpg (50.1 KB, 20 views)
File Type: jpg Focus Small.jpg (56.8 KB, 22 views)
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  #17  
Old 09-27-2013, 09:00 PM
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If I put the probe anywhere around the flyback, I get the same as in the focus picture in the previous post. Lots of ringing. Of course I don't know if that's just because I'm not making electrical contact and just picking up on the radiating signal.
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  #18  
Old 09-27-2013, 09:13 PM
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I scoped the leg of the diode that connects to the 500ohm resistor that feeds the wiper of the ABL pot, blah, blah, blah. This is what I got. It's an ugly waveform, that's for sure, but what does it mean? It was with a volts/div of .2 and a time/div of 20us.
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File Type: jpg ABL Diode Scope Small.jpg (44.9 KB, 19 views)
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Last edited by TinCanAlley; 09-27-2013 at 09:17 PM.
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  #19  
Old 09-27-2013, 10:17 PM
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It is really difficult to follow what is going on with the schematic incomplete and in a different thread.

Can you post a bigger chunk, so we see where the ABL signal from the pot wiper goes? Somewhere into the video amps, I assume.

Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.

Check the zener diode using the diode check on a DMM as a first go. That will conclusively check for opens/shorts. I'm betting it is still good though. Im thinking you might have a bad bypass cap in the video amp somewhere.
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  #20  
Old 09-28-2013, 12:29 AM
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Quote:
Originally Posted by N2IXK View Post
It is really difficult to follow what is going on with the schematic incomplete and in a different thread.

Can you post a bigger chunk, so we see where the ABL signal from the pot wiper goes? Somewhere into the video amps, I assume.

Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.

Check the zener diode using the diode check on a DMM as a first go. That will conclusively check for opens/shorts. I'm betting it is still good though. Im thinking you might have a bad bypass cap in the video amp somewhere.
The wiper goes directly to the base of the ABL transistor. From there it leaves the collector, through the contrast control and then on to the base of the base of the third video amp.

I'll do the B+ tomorrow. The DMM will tell me if the diode is working as far as passing in one direction. Wouldn't I need to supply 7.5V to open for testing in the other direction? Would a 9V battery do the trick?
Attached Images
File Type: jpg ABL Schematic 2.jpg (35.4 KB, 12 views)
File Type: jpg ABL Schematic.jpg (58.3 KB, 11 views)
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Last edited by TinCanAlley; 09-28-2013 at 12:39 AM.
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  #21  
Old 09-28-2013, 04:35 PM
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Quote:
Originally Posted by N2IXK View Post
Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.
Okay, here's the B+. The DMM has it at 129.8V and the waveform is attached. It doesn't look clean at all. Not sure why there are two on the scope. Scope had the 10x probe, volts/div of 1 and the time/div of 10us.
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File Type: jpg B+ Voltage Waveform.jpg (37.6 KB, 14 views)
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  #22  
Old 09-28-2013, 05:03 PM
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Okay, I just scoped the B+ at the test point which gets it directly from the source and something odd is happening to the waveform. Hopefully someone here has the answer.

Take a look at the two attached pics. The first one is the rippled wave form with a thin trace line. Then take a look at pic two. The line is starting thin and spreading out, then back, then out, etc. It takes about 4 to 5 seconds for the process and it keeps repeating.

So what would cause this?
Attached Images
File Type: jpg B+ Waveform thin.jpg (49.0 KB, 8 views)
File Type: jpg B+ Waveform spreading.jpg (52.8 KB, 10 views)
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  #23  
Old 09-28-2013, 06:24 PM
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Quote:
Originally Posted by old_tv_nut View Post
What you called the "ground" of the tripler is not ground, it is just the low point and has some positive voltage on it due to being connected to ground through the other parts of the circuit, not directly to ground. If the Zener was connected on both ends to ground, it would indeed be doing nothing.
I think TCA is taking tripler ground to mean GROUND and of course its not.

OK TCA the "ground" on the tripler is grounded in SOME sets.
On those the ABL will usually be taken at R356, the "low" end of the
FBT HV winding.
Think of yours as the low side of the tripler.
R362 & R359 will have the HV current through them, the brighter
the pix the more current so more voltage across the resistors.
The Zener diode will keep the voltage at its cathode at
7.5 V or less.
Under 7.5V the zener does nothing.
Result is the ABL control will adj. between apx 0 V & 7.5 V
If a dark pix it will adj. between 0 & < 7.5 V & send that to the
ABL transistor.

Hope that helps

73 Zeno
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  #24  
Old 09-28-2013, 06:37 PM
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Quote:
Originally Posted by zeno View Post
I think TCA is taking tripler ground to mean GROUND and of course its not.

OK TCA the "ground" on the tripler is grounded in SOME sets.
On those the ABL will usually be taken at R356, the "low" end of the
FBT HV winding.
Think of yours as the low side of the tripler.
R362 & R359 will have the HV current through them, the brighter
the pix the more current so more voltage across the resistors.
The Zener diode will keep the voltage at its cathode at
7.5 V or less.
Under 7.5V the zener does nothing.
Result is the ABL control will adj. between apx 0 V & 7.5 V
If a dark pix it will adj. between 0 & < 7.5 V & send that to the
ABL transistor.

Hope that helps

73 Zeno
Makes perfect sense. I will file it away in my memory and hope what I've learned will help with the next lesson.
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  #25  
Old 09-28-2013, 06:40 PM
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Quote:
Originally Posted by TinCanAlley View Post
Okay, here's the B+. The DMM has it at 129.8V and the waveform is attached. It doesn't look clean at all. Not sure why there are two on the scope. Scope had the 10x probe, volts/div of 1 and the time/div of 10us.
Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno
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  #26  
Old 09-28-2013, 06:46 PM
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Quote:
Originally Posted by zeno View Post
Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno
It is the B+ directly off of the transformer and the pin is noted on the topside by a tag that says "B+".

So I should be locating the 240V B+? I'll see if I can locate it on the schematics.

Oh, and C270 was changed during the initial recap when I got the set.
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  #27  
Old 09-28-2013, 07:04 PM
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Quote:
Originally Posted by zeno View Post
Is that the main B+ or one of the video outputs ???
The video out B+ is 240 VDC & filtered by C270. This cap
is notorious for causing jailbars in almost any brand.
Check C270 before going further.
In any case there is 5V of garbage there that shouldnt be.........

73 Zeno
Here's the B+ 240V that feeds the video outputs. Again, I don't know why I sometimes get two traces. I don't have a reference waveform to compare it to, but it does seem that there is ringing in it.
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File Type: jpg B+ 240V Boost.jpg (56.8 KB, 14 views)
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  #28  
Old 09-28-2013, 08:20 PM
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Quote:
Originally Posted by TinCanAlley View Post
Here's the B+ 240V that feeds the video outputs. Again, I don't know why I sometimes get two traces. I don't have a reference waveform to compare it to, but it does seem that there is ringing in it.
There is no way to tell if this is significant if you don't tell us the volts/division setting of your scope so we know what the peak-to-peak value of this waveform is.

Edit: I see you did tell the settings on a previous waveform. I suggest you check the filter cap as suggested by Zeno.

Last edited by old_tv_nut; 09-28-2013 at 08:24 PM.
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  #29  
Old 09-28-2013, 08:21 PM
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What is the amplitude of that ringing on the 240V line? What is the DC voltage?

Can you try temporarily bridging another cap between 240V line and ground to see if it improves the bars or cuts the amplitude of that ringing?

Post the section of the schematic that shows C270 and this supply for those of without a Sams handy...
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  #30  
Old 09-28-2013, 09:14 PM
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Quote:
Originally Posted by old_tv_nut View Post
There is no way to tell if this is significant if you don't tell us the volts/division setting of your scope so we know what the peak-to-peak value of this waveform is.

Edit: I see you did tell the settings on a previous waveform. I suggest you check the filter cap as suggested by Zeno.
It had the 10x probe on volts/div of 5 and time/div of 20.

I'll double check the cap. I is new and tested good w/in spec when I tested it before install.
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Last edited by TinCanAlley; 09-28-2013 at 09:26 PM.
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