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#46
05-30-2021, 12:40 PM
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために 
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#48
05-30-2021, 02:38 PM
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#49
05-30-2021, 03:31 PM
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#50
05-30-2021, 03:32 PM
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EDIT if you have not replaced them yet, do it NOW, as someone once once told they will ALWAYS be bad, and/ or out of spec. this proved correct in my ctc-16 and GE ctc-15 clone, I put 1w parts.
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために Last edited by Yamamaya42; 05-30-2021 at 03:38 PM.
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#51
05-30-2021, 05:08 PM
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OK, so a couple readings and waveforms with the analog scope today.
Double checking pin 7, V4... With video: 0v Without: -3.6v Scope: B4 V det: https://youtu.be/7qv-o0B_aHU After V det: https://youtu.be/GdDLbR7zWb0 Pin 7, V4 https://youtu.be/XtraunfLyd4 Pin 2, V4 https://youtu.be/Yiq7CfYEB8s Replacement Nuvistor ordered, as the current one has bad grid leakage. Just a hunch, there may be excessive noise coming in from the tuner AGC because of this, combined with the boost voltages applied later in the IF, could be distorting the video waveform at some point.
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#52
05-30-2021, 05:48 PM
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To get clearer scope traces:
Set horizontal sweep to 10 us / div. This will display somewhat more than one video line period (=63.5 usec) Set vertical gain to calibrated position so you are not reading an unknown amplitude such as > 1 v/div ("greater than"). Adjust trigger level to trigger on H sync pulses All you can tell from what you have posted is that you have video (but you knew that because you have a picture). Then, if you can put up a still image that shows the white smear following a black block on a plain background, you may be able to see it on the scope, and see which places in the circuit it appears. If you don't have any test pattern sources, try to find a DVD that shows the problem when you pause it. Edit: A still image will also allow you to see the effects of any adjustments without getting confused by varying video content.
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#53
05-30-2021, 06:04 PM
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Another hint: for pin 7, you should set your scope to DC coupling and establish where 0 volts is on the scope screen with the vertical centering control. Then you can see the actual voltage range on the grid.
Some things I don't understand right now: Why is the DC on pin 7 zero volts with video? The detector diode is working negative with respect to ground, so any IF signal should pull the grid negative. Why does pin 7 go negative with no video (I assume you mean no RF signal?). Does the scope show a lot of random noise there with no RF? If so, and you don't see snow on the screen, this would mean the tuner and IF are fine and something is causing the noise to be suppressed before it gets to the output (perhaps the noise inverter).
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#54
05-30-2021, 06:13 PM
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Thanks for posting scope videos, feel free to post 1 or 2 full
minutes of tape in the future. In your first 2 videos it sure looks like there is a lower frequency noise floating through the semi-synced picture. While looking at a longer scope run, you should sweep the sweep speed setting and see if you can capture the noise. The last one looks more normal. With that V4 Pin 7 voltage back to 0V with video I think you should replace those 2 resistors mentioned above. You can expect in circuit resistance measurements to be somewhat accurate if the value of the resistor is .5 Ohms to possibly 20K. Anything over 100K you should expect a 90% chance of complete inaccuracy. You might also want to at this point check out that entire AGC line back to the tuner. From those 2 resistors R 48 & R 50 keep going back to the tuner, & check that .5V at the end of that line. See what you get. .
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Yes you can call me "Squirrel boy"
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#55
05-30-2021, 06:18 PM
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Yes, I also expected a different voltage at pin 7 with no video.
he needs to slow the sweep and try and find that noise. It may even be heater to cathode noise getting into the detector. .
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Yes you can call me "Squirrel boy"
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#56
05-30-2021, 08:27 PM
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Correct me if I'm wrong, but didn't the OP figure out that the smearing is there if he injects video at the first video amp and gone if he injects it at the second video amp?
If that's the case he should fix it so that he can get smear free video when injecting at the output of the video detector before worrying about the front end and IF sections. I'm not saying the front end doesn't have issues, but if there's issues in the video stages too then they will hide any progress or other issues in the front end and IF stages. When you have multiple problems in a TV there's often an optimal and a counter-productive order to tackle them in.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 Last edited by Electronic M; 05-30-2021 at 08:42 PM.
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#57
05-30-2021, 08:31 PM
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A lot of good feedback and apologies for my crude scope pix.
And, ok ok you've twisted my arm on the 2 resistors. Just about every resistor I've pulled from that set has been reasonably within spec, but maybe those 2 just get an unusual hammering for some reason, so I'll take a closer look. Last edited by Jon1967us; 05-31-2021 at 02:07 PM.
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#60
07-09-2021, 10:23 PM
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That TV video IF response curve that looks like a square wave with peaks on the ends is not created by injecting a square wave into the TV. It's created by an IF sweep generator. An IF sweep generator is essentially an an overcomplicated radio alignment generator. It generates a wine wave frequency in the TV IF range and contains a 60Hz ramp wave generator the ramp wave modulates (sweeps) the IF output frequency from around 3MHz below the center to around 3MHz above it. So the sweep generator outputs a constant amplitude RF signal (the frequency of which constantly changes such that it sweeps the entire IF passband at roughly 60Hz), and the 60Hz signal is also output. The 60Hz feeds the horizontal axis of the oscilloscope, and the vertical axis of the scope is fed from a demodulator probe connected to the TVs IF. Basically the sweep generator and the scope form an RF curve tracer (or primitive RF network analyzer if you are familiar with RF network analyzers) that traces the IF response on screen by feeding the TV IF input a constant amplitude signal that sweeps it's frequency response range, sweeping the scope horizontal in sync with the frequency and ploting the non-constant output (which is the response curve) on the scopes vertical axis. A marker generator is basically an RF wine wave generator with very precise frequency. TV specific ones can create multiple marker frequencies simultaneously and usually use crystal oscillators. You can use a modern digital RF generator or even an old tube radio RF generator (and a modern digital frequency counter to precisely adjust it) instead or in addition to a TV specific marker generator. The marker generator adds extra fixed frequency energy to the signal injected into the TV IF creating a thing vertical line above and below the response curve on the scope to tell you if your response peaks are at the right frequency (because the sweep generator sacrifices frequency precision/accuracy to perform the sweep). If alignment is a complex involved process that requires a lot of specialized equipment, knowledge and practice (it's nearly as much art as science) to do well.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 Last edited by Electronic M; 07-09-2021 at 10:34 PM.
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