Sony KV-4000 Troubleshooting Questions

[crtfool]

I just acquired a KV-4000 that needs attention in the following 2 areas. Any assistance that you can provide is very much appreciated - thanks in advance.

I am getting dark horizontal banding wherever there is a light area on the screen - for example, if there is a line of 1/2" white text on a light blue background in the center of the screen, then the whole 1/2" horizontal area will be a darker blue band there - the text is not smearing, and it is razor sharp. When watching a DVD through the video input, there will be numerous occurrences on the screen as the scene changes. I am not using the built in tuner, I am only using the monitor inputs. Not sure what this is, but adjusting brightness and contrast do not affect it.


There are markings for horizontal centering and vertical centering on the board, but I do not see any adjustments on either side of the board - no VR pots, no switches, no plug in pin - the horizontal centering is way off to the left. How would I adjust this?

[kx250rider]

Hard to tell, but I'd guess it's a maybe a bad electrolytic in the video output or in the G1 lines. If you have a schematic, look for a low value high voltage cap (maybe 4.7 @ 160v or @250v, etc), very near where the G1 voltage goes to the CRT. It might be physically near the flyback, or on the CRT socket board itself. Just a guess here....


Charles

[crtfool]

Charles - Thanks for the info. I do not have a service manual yet, but will be getting 1 soon. I will recheck the caps, and look for 1 that fits your suggestion.

[kx250rider]

Originally Posted by crtfool

Charles - Thanks for the info. I do not have a service manual yet, but will be getting 1 soon. I will recheck the caps, and look for 1 that fits your suggestion.

You're welcome. And I hope I'm not giving you a bum steer....

I just looked, and my KV-4000 and KV-4100 manuals are missing, so I must have lent them out and forgotten . As said, just look on the socket board for any electrolytic, and follow the wires from the "g1" pins back to where they go on the main board (or HV board; I can't remember how the layout is in that set), and look there. But I wouldn't spend a lot of time beyond that, until you have at least a basic schematic for it. There is one with the original paperwork with each of those sets when new, and it's usually still in the plastic bag if the owner kept it. So if a fellow AKer has one, maybe they'd put up a picture of that section?

Charles

[crtfool]

Charles - I finally got back to checking the capacitors - there is 1 cap c522 that is 10uf @160v - the ESR is .5

Could this problem be caused by the horizontal centering being all the way to the left - causing the beam to reflect off the side of the CRT? Do you know how to adjust the horizontal centering? - see picture

[kx250rider]

I don't think that cap would cause a centering problem, but it might indeed be causing a smear, and I'd replace that cap anyway based on the ESR reading (assuming it isn't being read falsely in circuit). What I see in your photo, looks like a smear (bad cutoff). I see that the cap you mention, comes off a leg of the flyback called "video", so I'd assume that's feeding the luminance channel. Again, it's really tough to guess on these things, and if it's a centering issue (or a really really bad horizontal linearity strech), I'd be looking for trouble elsewhere. If it means anything, I don't remember ever having a horizontal linearity or centering problem on any Sony. The centering might either be a jumper plug, or a pot someplace on the sweep board, even though you see the markings and no adjustment nearby. Those boards were also used in color camera viewfinders, and in industrial monitors, so there were various configurations built. I wish I had the schematic handy, as I'd try to give better advice. It is somewhat possible that the consumer version has no adjustments for the centering, but if that's the case, you could probably still adjust it by changing the value of a resistor in the horizontal circuit, which would be nearly impossible without the schematic.

Charles

[crtfool]

Hi Guys,

I decided to revisit this problem by adding 2 new pictures to more clearly show what I am talking about regarding the banding problem. Please disregard the blurriness of the pictures - I am more interested in showing a banded picture and a clear picture, not resolution or focus.

I have since acquired a second set in much better condition, but it does the exact same thing. Both sets do have serious horizontal over-scan, not sure if it has anything to do with this problem.

[jhalphen]

Hi David,

Wow! that is severe indeed, the first picture is really revealing.

Just a gut feeling, but i would say that the KV-4000 is not necessarily the culprit.

OK, let's talk about your video sources, the KV is being used as a monitor running from a DVD, correct?

You're using a baseband video signal not an RF channel 3-4 out from the DVD, correct?

I would switch sources: NTSC out from an ATSC box, cable box, a second DVD player. Does the banding occur on other sources?

Is the banding fixed, moving, linked to picture content?
Permanent or random?

Have an oscilloscope connected to the KV's video input simultaneously and set it up as a WFM display, look at the signal in both H and V scan rates, do the bands show up simultaneously on the Sony and the scope?

Have you tried the DVD player on another video monitor? - all OK?

When the banding occurs, if you turn down the Chroma to zero, is it still there?

Do you have an NTSC generator, have you tried it on the Sony?

Try various signals with full black to white content: grey scale, convergence crosshatch. If the banding is related to luminance levels, video amp instability for instance, it could show up.

investigate silly causes: measure if there is a DC potential on the DVD's video out. One of mine did and it played havoc with my Broadcast routing switcher which is DC circuitry throughout. Inserting a big 470 Mfd Cap in the video feed solved the problem: crushed whites, smeary color & noise.

Keep us informed of the results of your tests.

Best Regards

jhalphen
Paris/France

[crtfool]

Originally Posted by jhalphen

Hi David,

Wow! that is severe indeed, the first picture is really revealing.

Just a gut feeling, but i would say that the KV-4000 is not necessarily the culprit.

It is definitely the TV - Both of my KV-4000's do it.

Originally Posted by jhalphen

OK, let's talk about your video sources, the KV is being used as a monitor running from a DVD, correct?

You're using a baseband video signal not an RF channel 3-4 out from the DVD, correct?

I would switch sources: NTSC out from an ATSC box, cable box, a second DVD player. Does the banding occur on other sources?

Is the banding fixed, moving, linked to picture content?
Permanent or random?

These pictures were taken from an over the air broadcast with the TV tuned to channel VHF 12. The signal was from my DVR - freeze framed during the broadcast - I stopped it on a very bad frame and a perfect frame for the pictures. The banding came and went according to the image on screen. If I looped a portion of the video - the exact image would be shown each time without variation. It also does it with a DVD player on the video input too.

Originally Posted by jhalphen

Have an oscilloscope connected to the KV's video input simultaneously and set it up as a WFM display, look at the signal in both H and V scan rates, do the bands show up simultaneously on the Sony and the scope?

I do not have a scope - I do not do that much work to need one. Not necessary though - see below explanation.

Originally Posted by jhalphen

Have you tried the DVD player on another video monitor? - all OK?

Yes - it is perfect on all the other sets in my collection.

Originally Posted by jhalphen

When the banding occurs, if you turn down the Chroma to zero, is it still there?

Color, Tint, Brightness, Picture controls have no effect.

Originally Posted by jhalphen

Do you have an NTSC generator, have you tried it on the Sony?

Do not have one. Not necessary though - see below explanation.

Originally Posted by jhalphen

Try various signals with full black to white content: grey scale, convergence crosshatch. If the banding is related to luminance levels, video amp instability for instance, it could show up.

investigate silly causes: measure if there is a DC potential on the DVD's video out. One of mine did and it played havoc with my Broadcast routing switcher which is DC circuitry throughout. Inserting a big 470 Mfd Cap in the video feed solved the problem: crushed whites, smeary color & noise.

Keep us informed of the results of your tests.

Best Regards

jhalphen
Paris/France

An accidental discovery:

The fact that these sets have a very large horizontal over-scan keeps bothering me. If you compare the same image on this set and a different model completely, you will see that the KV-4000 has a very stretched horizontal image - a lot is cut off on both sides. I keep thinking that the beam is getting reflected off the internal sides of the CRT.

I was previewing the TV guide built into my DVR to gauge the horizontal stretch. When the guide is displayed, the program content is reduced to a small window at the top right corner of the screen - I accidentally noticed that the image was perfect when it was reduced to this size. I watched 10 minutes of the program this way - no banding or flashing. I then rewound this same portion and watched it full screen - banding and flashing all over the place.

I am convinced that the problem will be eliminated if I can reduce the horizontal over-scan.

[old_tv_nut]

I think it might be a horizontal sync / video clamping problem. Look for caps in the video input circuit.

Does this set have a horizontal hold control? If so, what happens on the bad picture when you turn the control? Maybe clamping black/sync level on video near the edge of the picture?

[old_tv_nut]

Also strange that white "Coby" letters cause dark bar, but white objects in the other scene cause a bright bar - I don't have a good explanation for the difference.

[AiboPet]

AGC problem maybe? One that may be common for THAT set? (so BOTH sets)

I do have a little Sony 8mm player that does NOT like my inhouse transmitter when using it's little snap-on tuner. It acts like I'm overpowering it. It doesn't mind the A/V inputs, and plays it's 8mm tapes just fine. It even receives "other" analog stations in the area "just okay"...but HATES the setup in the apartment (which ALL the old sets are fine with).

I noticed it seems to be easy to overwhelm some Trinitron set.

[Eric H]

Have you tried a different DVD player?
Coby isn't exactly top drawer stuff, it could have a problem, or possibly just not be very good.
It just seems odd that both sets do the same thing.

[jhalphen]

Hi David,

From Page 24 - D Board adjustments in the KV-4000 Service Manual which you kindly gave to me there is a section on changing the value of C531 to change the horizontal width - see enlarged page snapshot.

C values to be tried go from 0.0022 for the narrowest width to 0.0082 for the widest.

I would first replace the existing cap by a same value new one just in case the original was bad.

If no change, then try a 0.0022.

Does the H width reduce?

Problem solved?

Note:
You say that the TV was receiving OTA NTSC on Channel 12 from its own tuner. Did the TV show the problem directly off-air?

Question: is the DVR recording the same signal in parallel with the KV-4000 from it's own off-air tuner and you then use it as a frame-by-frame replay device.

or is the DVR fed from the KV-4000's VHF tuner using the Video Out connection?

Best Regards

jhalphen
Paris/France

[crtfool]

Originally Posted by jhalphen

Hi David,

From Page 24 - D Board adjustments in the KV-4000 Service Manual which you kindly gave to me there is a section on changing the value of C531 to change the horizontal width - see enlarged page snapshot.

C values to be tried go from 0.0022 for the narrowest width to 0.0082 for the widest.

I would first replace the existing cap by a same value new one just in case the original was bad.

If no change, then try a 0.0022.

Does the H width reduce?

Problem solved?

I was looking to fix the horizontal size with the yoke - and yes, I spelled it right this time - connections with L901 and L902 connections, but could not figure out what they meant to do. I removed C531 completely - the width did reduce, but not completely for the frame to fit edge to edge, compared to other sets with the same signal. The capacitor was factory installed - marked 153K, which is a 0.015 - much larger than the largest listed cap for maximum width. Since it is now an open circuit, the width should be at it's narrowest.
I previously shifted the horizontal center to the right, and the vertical center down. I readjusted the vertical size and linearity. The image is now perfectly in frame on top, bottom, and right side - but still very much over-scanned on the left. When I watch it in the TV Guide preview window - the image is complete on all 4 sides, and there is no banding or flashing. In full frame view, there is still some banding and flashing, but nothing as severe as before. If I can figure out how to reduce the over-scan on the left, I think the problem will be solved completely.

Originally Posted by jhalphen

Note:
You say that the TV was receiving OTA NTSC on Channel 12 from its own tuner. Did the TV show the problem directly off-air?

Question: is the DVR recording the same signal in parallel with the KV-4000 from it's own off-air tuner and you then use it as a frame-by-frame replay device.

or is the DVR fed from the KV-4000's VHF tuner using the Video Out connection?

Best Regards

jhalphen
Paris/France

The DVR was connected to my mini transmitter via composite cables, broadcasting on channel VHF 12, and picked up by the KV-4000 internal tuner. But, the way the signal gets into the TV does not matter - the effect is the same regardless of the connection.