KV9200 Issues

[vol.2]

First a little background. I got this set in about 1992, and used it sporadically for about 12 years before mothballing it in storage. It worked very well and had a bright tube when I got it, and I didn't put a lot of wear on it myself.

I got it out of storage recently for a project, and it needed to have basically all of the electrolytics replaced. Several of them had corroded away to nothing, and all but a few were way, way out of spec and drying out.

So I finished a full recap, and set it up as per the service manual a

nd the Sams.

It works okay, and is still pretty bright, but it's got a few lingering issues that I'm not sure what to do about.

1) In some material (not all), there is horizontal lines in the colors. This seems to be stronger when I turn down the brightness. So far, it only happens with one of the DVDs I tested. The lines are strongest in the Red, but I have also noticed them in Blue. I don't (or can't) see these lines in other things I have tested in the same DVD player (so far). The DVD that does show these lines seems fine on other TVs.

2) I followed the setup instructions, and it says I should set the BKG dials at halfway, the DRIVE dials at full, and adjust a crosshatch for best grey at the BKG dials. The BLUE crosshatch comes up first, but it's only the vertical lines, not the horizontal lines which take a lot more background to make appear. Red and Green do not appear to have the same issue, and the horizontal lines do appear as bright as the vertical lines. Because of this issue, I was unable to set the white balance this way, and I had to use a black background and just do the whole screen to grey. This eventually worked after a whole lot of back and forth and looking at greyscale images, but I can't help feeling like this issue with the Blue being much stronger vertically is a problem, especially since it doesn't effect the Green or Red.

I was thinking maybe I should try replacing the BKG and DRIVE transistors and see how that goes. I don't know what else I could try. This is the output section of the schematic:





3) The Sam's references a "Beat Pattern," when adjusting the 4mHz trap. It wants me to adjust the fine tuning on strong signal until I get a "beat pattern," and then turn a pot until that goes away. I don't know what a beat pattern is. Any help with that?

4) The Sam's also wants me to use a sweep generator for some of the setup stuff. I don't have one. I have a scope, a signal generator, and a pattern generator. Can I use the function generator in place of a sweep generator in this fashion?



5) The Horizontal Oscillator seems flakey. I followed the instructions, which is to ground the transistor on the Oscillator and adjust the control until the image stops floating, but I couldn't really get it to stop completely. I could get it right to the point when it starts to drift in the other direction, but it floats around enough that it will move back and forth by itself if I leave it alone. I don't know how much of an issue this is, but I thought if it was, I might need to replace a transistor, or maybe a pot with more turns will allow me to get it more accurate?




Thanks

[old_tv_nut]

1) Don't understand what "horizontal lines in the colors" means. Can you post a picture?
2) No idea why blue vertical lines are stronger than horizontal lines. Maybe a shorted coil?
3) A "beat pattern" means stripes or herringbone interference in the picture. If your signal has audio content, the pattern will move along with the audio content. You should easily recognize it as something that doesn't belong there.
4) If the setup requires a sweep generator, you must use a sweep generator. This is the case for IF alignment and color alignment if the service instructions say so. The good news is that these seldom change, especially not in solid state sets, as long as components have not failed, so the best bet is to skip alignment and see if the picture and sound are OK without it.
5) The H oscillator will float a bit normally just from random voltages in the chassis. The important thing is that it's not skewed entirely one way or the other. Going back and forth a bit is fine. When you remove the ground, it should lock up, and that's all you need.

[vol.2]

Thanks for the reply

Originally Posted by old_tv_nut

1) Don't understand what "horizontal lines in the colors" means. Can you post a picture?

This is the best I can do. The horizontal lines through the characters are what I'm talking about. They appear in different shades depending on the color they run through. It only (so far) happens with this DVD.

2) No idea why blue vertical lines are stronger than horizontal lines. Maybe a shorted coil?

That doesn't sound good. I wouldn't know how to test for that either.

3) A "beat pattern" means stripes or herringbone interference in the picture. If your signal has audio content, the pattern will move along with the audio content. You should easily recognize it as something that doesn't belong there.

Ok. I didn't see anything like that. The instructions say that such a pattern should appear as I use the fine tuning and move it away from the station. When I do that, it goes black and white counterclockwise, and turns to snow as I go clockwise. There doesn't seem to be much of a transition either way

4) If the setup requires a sweep generator, you must use a sweep generator. This is the case for IF alignment and color alignment if the service instructions say so. The good news is that these seldom change, especially not in solid state sets, as long as components have not failed, so the best bet is to skip alignment and see if the picture and sound are OK without it.

Well, I had to replace a lot of caps. I think this set runs pretty hot due to the small size and almost all of them were toast. So I guess it's okay, but I thought maybe replacing the caps would mess with the RF.

5) The H oscillator will float a bit normally just from random voltages in the chassis. The important thing is that it's not skewed entirely one way or the other. Going back and forth a bit is fine. When you remove the ground, it should lock up, and that's all you need.

Okay, thanks. It made it seem like in the Sams that there would be a spot that it locks as I mess with the pot. It's good to know it doesn't matter. I definitely got it so it isn't skewed at least.


I realized there was one other thing I was wondering about:

6) The focus on this set is handled by moving a jumper wire from a resistor to one of three positions. There's zero volts, something like 130V, and 530V. It seems like zero volts is too little, and 530V is too much, but 130V doesn't look to my eye to be quite right either. Is it crazy to just put a variable resistor between 530V and ground and just tune it in like I would on a set with a focus pot?

Thanks again!

[zeno]

A little at a time...... Make as good a B&W pic as you can. Forget
the color for now.

Be sure the cap on source #7 ( 4.7mfd ?) has been changed.
Put real content NOT a generator on it.
Turn off all auto color controls & color control all the way down.
Contrast & bright about 3/4 up.
Be sure you can turn the brite down all the way down to no pix or
very dim pix. If not turn down G-2 a little.
If it looks like it has bad convergence adj the H-STAT control.

Now go to manual & put R-B-G controls at the start point, Make the
pix as B&W as you can. Then we can take it from there.

BTW the lines you see are the phosphor stripes.
The CRT is a low focus type & moving the jumper seldom makes a difference.
You could use a pot but use a 1 watt & be sure it runs cool !

73 Zeno
LFOD !

[old_tv_nut]

1) only happens with one DVD? Then it's the DVD. Looks to me like the DVD may be a copy of a videotape that had some defects.

2) Since there are similar coils in R,G, and B circuits, you can compare them. One way to detect a shorted coil would be with an ohmmeter, but the low resistance values may be hard to measure accurately. Another thing you could try is connecting a short wire across a coil in the red or green circuit and see if it gives the same effect as you see in the blue. If it does, then try shorting the corresponding blue coil to verify that the added short doesn't change the problem; in other words, the coil in the blue section was already shorted. Of course, I am only guessing about the possible cause, and you may find that the coils are OK and the problem is something else.

3) If you're not seeing a beat pattern, the best bet is that the adjustment is already optimum, so just leave it alone.

4) Caps that would affect the alignment are small pf values associated with IF coils/transformers, and seldom fail, so are not usually replaced when re-capping. Typically needing recapping are electrolytics and paper caps with much larger values, like nanofarads (thousands of picofarads) and upward to microfarads. If the picture and general operation of the set is OK, alignment is not needed, and is only an educational exercise.

[vol.2]

Originally Posted by zeno

A little at a time...... Make as good a B&W pic as you can. Forget
the color for now.

Be sure the cap on source #7 ( 4.7mfd ?) has been changed.
Put real content NOT a generator on it.
Turn off all auto color controls & color control all the way down.
Contrast & bright about 3/4 up.
Be sure you can turn the brite down all the way down to no pix or
very dim pix. If not turn down G-2 a little.
If it looks like it has bad convergence adj the H-STAT control.

Now go to manual & put R-B-G controls at the start point, Make the
pix as B&W as you can. Then we can take it from there.

Ok. I'll start over with it. The yoke got loose at some point while it was in storage so my purity was pooched and I had to mess with it. I got it to a "decent" place, but it could be a little better. It's sorta difficult when pretty much everything needed to be adjusted somewhat to know what to work on first.

The CRT is a low focus type & moving the jumper seldom makes a difference.

Yes, they didn't help, but the "middle" value, which is about 200V is the factory setting, and it's the closest to good focus out of the three. The higher voltage is about 500V, so I figured the most ideal spot would be somewhere between 200-500V, and pot would be useful.

You could use a pot but use a 1 watt & be sure it runs cool !

Does that mean I need to get a 500V, 1 watt pot? It's going to be pretty big, also expensive. Not sure this set is worth that, but it might be interesting as an experiment anyway. I found this one on mouser: https://www.mouser.com/ProductDetail...B2102MAB251S22

Originally Posted by old_tv_nut

1) only happens with one DVD? Then it's the DVD. Looks to me like the DVD may be a copy of a videotape that had some defects.

Good point.

2) Since there are similar coils in R,G, and B circuits, you can compare them. One way to detect a shorted coil would be with an ohmmeter, but the low resistance values may be hard to measure accurately. Another thing you could try is connecting a short wire across a coil in the red or green circuit and see if it gives the same effect as you see in the blue. If it does, then try shorting the corresponding blue coil to verify that the added short doesn't change the problem; in other words, the coil in the blue section was already shorted.

By coils, you're referring to the coils on the neck board attached to the RGB output transistors, correct? It's weird, but the service manual and the Sam's both give different values for them, so I'm not actually sure which they should be. I could pull them and measure them. I have an LCR meter. The Sam's says 1.5uH, the Sony manual says 8.2uH. Go figure.

I am only guessing about the possible cause, and you may find that the coils are OK and the problem is something else.

Yeah, that's why I was considering just getting a few new output transistors and replacing them. I'm sure I can find something beefier that will at least be more robust, even if it doesn't fix anything. Maybe a Motorola MPSU10 or something?

3) If you're not seeing a beat pattern, the best bet is that the adjustment is already optimum, so just leave it alone.

Makes sense.

4) Caps that would affect the alignment are small pf values associated with IF coils/transformers, and seldom fail, so are not usually replaced when re-capping. Typically needing recapping are electrolytics and paper caps with much larger values, like nanofarads (thousands of picofarads) and upward to microfarads. If the picture and general operation of the set is OK, alignment is not needed, and is only an educational exercise.

Yeah, the yoke moved around in storage and the purity was garbage. I had to move it around a bit, and then I realized it needed a bit of fine tuning. I'm tyring to sort out what might still be an electrical problem with what's just in need of adjustment.

Thanks everyone. I'm probably going to place another order to Mouser this week, so I'm trying to finalize if I need anything else for this particular project.

[old_tv_nut]

"By coils, you're referring to the coils on the neck board attached to the RGB output transistors, correct? It's weird, but the service manual and the Sam's both give different values for them, so I'm not actually sure which they should be. I could pull them and measure them. I have an LCR meter. The Sam's says 1.5uH, the Sony manual says 8.2uH. Go figure."

I mean any of the six coils that are the same in R,G, and B: L702, 703, 704, 302, 306, 307.

I just noticed that C701 (blue channel) is 560 pf and the correspong R and B caps are 390 pf. This could be making the difference, though I'm not sure why they would do that.

[vol.2]

Originally Posted by old_tv_nut

I just noticed that C701 (blue channel) is 560 pf and the correspong R and B caps are 390 pf. This could be making the difference, though I'm not sure why they would do that.

Well, thinking about it, the only difference I can see is that the RGB drive signals are all different voltage levels as they come out of demod. Red is 4V, Blue is 5.8V, and Green is 1.5V. I've seen this arrangement (not necessarily the exact same voltages) in other sets before, although I don't understand why it is. Perhaps related to that somehow?

[old_tv_nut]

Those differences in color difference signal levels with a rainbow generator are because the R-Y and B-Y signals in a normal video signal are scaled down before modulation on the color subcarrier to prevent overmodulation on particular colors. With a color signal of real color bars or program video, those differences in gain restore the final R, G, and B signals to the right level once the luminance signal is added. For example, full amplitude saturated green bar has luminance of 59% of white, so the G-Y only has to make up 41% to turn green on completely. (The final values of R, G, and B for white may not be equal due to differences in R, G, and B phosphor efficiency, plus NTSC sets typically had increased R-Y gain to make up for the yellowish modern green phosphor.) Since the rainbow pattern consists of constant amplitude subcarrier, it does not have prescaling depending on hue, and therefore the gain differences in the color difference demodulators show up.

[ARC Tech-109]

It's the copyguard causing the issues, they insert a 180 phase inversion in so many horizontal lines to thwart the chroma AFC in the color under VCRs. Look at the signal on a pulse cross monitor and turn the color up. Your Sony is slow to respond to the phase inversion

[vol.2]

Originally Posted by old_tv_nut

Those differences in color difference signal levels with a rainbow generator are because the R-Y and B-Y signals in a normal video signal are scaled down before modulation on the color subcarrier to prevent overmodulation on particular colors. With a color signal of real color bars or program video, those differences in gain restore the final R, G, and B signals to the right level once the luminance signal is added. For example, full amplitude saturated green bar has luminance of 59% of white, so the G-Y only has to make up 41% to turn green on completely. (The final values of R, G, and B for white may not be equal due to differences in R, G, and B phosphor efficiency, plus NTSC sets typically had increased R-Y gain to make up for the yellowish modern green phosphor.) Since the rainbow pattern consists of constant amplitude subcarrier, it does not have prescaling depending on hue, and therefore the gain differences in the color difference demodulators show up.

Ok thanks. So those voltages are assuming an NTSC test pattern. I'm sure it says that in the Sam's and I forgot. There's a lot to remember

Originally Posted by ARC Tech-109

It's the copyguard causing the issues, they insert a 180 phase inversion in so many horizontal lines to thwart the chroma AFC in the color under VCRs. Look at the signal on a pulse cross monitor and turn the color up. Your Sony is slow to respond to the phase inversion

I see. That's really interesting. It's good to know what was causing that. Interesting also that it only shows up one DVD out of all that I've tried. It's not nearly the newest DVD I have either.

But actually, that was a separate issue. old_tv_nut was trying to help me figure out why the Blue vertical lines seem to be so much stronger than the Blue horizontal lines when displaying a crosshatch pattern from a B&K pattern generator. The Red and Green seem to come up in equal intensity.

He was suggesting that the capacitor in the Blue area seems to be a different value for some reason and that might be why.

I'm also still trying to figure out what I should order if I wanted to bodge a focus pot into the set. The optimal focus seems to fall somewhere in between the 200V setting and the 500V setting, so I wanted to get a pot and see how good I can get it. It was recommended I get a 1 watt pot, but 500V 1 watt pots are *huge*. The best I can find is like this https://www.mouser.com/ProductDetail...hfGtyjeA%3D%3D

I found a bunch of smaller 1 watt trimmers, but they are rated for like 400V.

[Alex KL-1]

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

[vol.2]

Originally Posted by Alex KL-1

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

Thanks! I figured as much. I was looking at the available devices and I think I'm going to buy the 500V pot. It's about $20, and I can reuse it in the future. I will tweak the pot until I find the right spot and then put a fixed voltage divider at the correct values and leave it.

That way I can take it out and use it again. Also, there isn't really a good spot to put such a device when it's closed, so it's better if I just put some 1 watt resistors in it's place.

I thinking about now how I would wire that in. Should I put in between the 500V source and ground? Seems like I should just use the F1 spot for the far side of the pot because it's zero volts.

[Alex KL-1]

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.

[vol.2]

Originally Posted by Alex KL-1

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.

Thanks Alex,

I looked on Mouser and Digikey, but the highest thing I can find in stock is a 1Mohm pot. It's a 2W bournes unit: https://www.mouser.com/ProductDetail...76JZfFDA%3D%3D

There's others in stock, but they all seem pretty similar.

Do you think 1M would be fine?