JVC D Series Horizontal Smearing on the Composite Input

[BenM86]

Curious if anyone else has had this issue and knows if it’s something that can be fixed/adjusted. I have a VCR and a Laserdisc player both with composite out, and both give me this issue with smearing when there are light colors on dark areas. It’s especially noticeable with on screen text. Image attached.

The s-video and component inputs don't do this. Both composite inputs do the same thing. And I tried the players with the composite input on my Panasonic plasma and no smearing issues there. So it’s something to do with the composite signal on the JVC specifically. Is there anything that can be configured in the service menu or caps that can be changed out to help? Or is this just how the comb filter is on this TV? Thanks!

[vol.2]

Originally Posted by BenM86

Curious if anyone else has had this issue and knows if it’s something that can be fixed/adjusted.

Smearing to the right of bright objects is an incredibly common and ubiquitous symptom that can point to a wide range of faults.

Worst case the tube is shot and the smearing is caused by excessive voltages driving the video output IC too hard.

Essentially, the output IC will have a maximum voltage range it can operate in, for example some voltage that represents the most dark thing on the screen (positive voltage) and something else that represents the brightest thing on the screen (ideally close to zero in most cases). If the tube is too worn out, you will have to increase that range because the cathodes will require you push a more negative-going voltage to achieve a bright enough picture to see. When that happens, you can see smearing to the right as the video IC goes into "clipping."

The effect is very similar to audio clipping, but it often manifests in the video in this stretching out of the video to the right of the brightest objects because the brightest objects represent the most negative-going voltages on the raster.

Otherwise, it's capacitors somewhere. If I had to guess in the power supply or the deflection area. I don't know JVC set too well, but if it was my set and I was serious about it, I would just go through and test them all. It would probably take a couple evenings.

You can also check voltages on the schematic and see if anything is off. That would lead you to most faults of the kind you are looking at.

[Alex KL-1]

I can add some ramblings...
Some processing IC will have less effective bandwidth intentionally for composite inputs, for not interfering with chroma and vice-versa. A simple filtering near the HF range (end range) will smear the signal. Since the mentioned effect not occurs with S-Video for example, this is potentially the culprit.
Unless the opposite occurs; eg. a composite input with more sharpness enhancement, just for making up the composite lesser performance. So, it calls for more HF signal amplitude and can make the effects that vol.2 mentioned in great detail. This is harder when the set uses a simple transistor video output; generally these have too high collector output resistor value (15k being common for a lot of models; better sets have it less than 8k2 and even 4k7) and smears details due to limited slew rate it can resolve.
LATE EDIT: or the sources, with the know difficulties to join the Y to the C signal and smears due to that (some sources are better than others for it).

[zeno]

My post from a few days ago on an MGA. only a few bucks to try.


Its probably the filter cap on the 200 V line. Its a top ten problem on
ALL sets. Symptoms are any combination of, or one of the following.

Pix goes from dark to light across the screen.
Pix just "not right",
Poor color, can look like bad CRT
Bright white raster with retrace lines.
Jail bars on left fading as you go right.
Streaking of brite content.
Cant turn brite down.
AND others that dont come to mind !

Zeno

Bottom line is change it on any SS set you are fixin !

[BenM86]

Originally Posted by vol.2

Smearing to the right of bright objects is an incredibly common and ubiquitous symptom that can point to a wide range of faults.

Worst case the tube is shot and the smearing is caused by excessive voltages driving the video output IC too hard.

Essentially, the output IC will have a maximum voltage range it can operate in, for example some voltage that represents the most dark thing on the screen (positive voltage) and something else that represents the brightest thing on the screen (ideally close to zero in most cases). If the tube is too worn out, you will have to increase that range because the cathodes will require you push a more negative-going voltage to achieve a bright enough picture to see. When that happens, you can see smearing to the right as the video IC goes into "clipping."

The effect is very similar to audio clipping, but it often manifests in the video in this stretching out of the video to the right of the brightest objects because the brightest objects represent the most negative-going voltages on the raster.

Otherwise, it's capacitors somewhere. If I had to guess in the power supply or the deflection area. I don't know JVC set too well, but if it was my set and I was serious about it, I would just go through and test them all. It would probably take a couple evenings.

You can also check voltages on the schematic and see if anything is off. That would lead you to most faults of the kind you are looking at.

If it was an issue with the output or with the tube wouldn't it be the same across all the inputs?

Originally Posted by Alex KL-1

I can add some ramblings...
Some processing IC will have less effective bandwidth intentionally for composite inputs, for not interfering with chroma and vice-versa. A simple filtering near the HF range (end range) will smear the signal. Since the mentioned effect not occurs with S-Video for example, this is potentially the culprit.
Unless the opposite occurs; eg. a composite input with more sharpness enhancement, just for making up the composite lesser performance. So, it calls for more HF signal amplitude and can make the effects that vol.2 mentioned in great detail. This is harder when the set uses a simple transistor video output; generally these have too high collector output resistor value (15k being common for a lot of models; better sets have it less than 8k2 and even 4k7) and smears details due to limited slew rate it can resolve.
LATE EDIT: or the sources, with the know difficulties to join the Y to the C signal and smears due to that (some sources are better than others for it).

Interesting. So possibly just an issue with how the set was designed?

Originally Posted by zeno

My post from a few days ago on an MGA. only a few bucks to try.


Its probably the filter cap on the 200 V line. Its a top ten problem on
ALL sets. Symptoms are any combination of, or one of the following.

Pix goes from dark to light across the screen.
Pix just "not right",
Poor color, can look like bad CRT
Bright white raster with retrace lines.
Jail bars on left fading as you go right.
Streaking of brite content.
Cant turn brite down.
AND others that dont come to mind !

Zeno

Bottom line is change it on any SS set you are fixin !

Certainly seems like an easy thing to try. Could it affect just the composite input?

[old_tv_nut]

If it was an issue with the output or with the tube wouldn't it be the same across all the inputs?
YES.

Interesting. So possibly just an issue with how the set was designed?
YES, BUT: you would expect filtering of the high frequencies (such as a chroma trap) to produce effects near the edges (which are there), but not that long smear far to the right.
Whatever it is, it must be something that is in the composite input circuit and not in anything common with the component signal.

[vol.2]

Originally Posted by BenM86

If it was an issue with the output or with the tube wouldn't it be the same across all the inputs?

Yes, it would, assuming the brightness/contrast is tracking correctly on the other inputs, and you would probably notice it if there was that big a difference.

Sorry, I didn't read your post carefully enough.

As tvnut pointed out:

Originally Posted by old_tv_nut

Whatever it is, it must be something that is in the composite input circuit and not in anything common with the component signal.

So that should actually make things a little easier, assuming you have a schematic to reference.

The first thing I would check is to see if there is a video signal level in the composite video section. If that pot exists and it's set too high, I think it could cause the smearing you see to the right. Like I said, I don't know JVC, but I've seen that on other Japanese sets for sure. The service manual should have a voltage level to set it at (if it exists).

If not, then focus on the parts in the composite input circuit. Check voltages everywhere and compare against the service manual. If anything looks fishy, pull caps and check them.

[BenM86]

Originally Posted by vol.2

Yes, it would, assuming the brightness/contrast is tracking correctly on the other inputs, and you would probably notice it if there was that big a difference.

Sorry, I didn't read your post carefully enough.

As tvnut pointed out:




So that should actually make things a little easier, assuming you have a schematic to reference.

The first thing I would check is to see if there is a video signal level in the composite video section. If that pot exists and it's set too high, I think it could cause the smearing you see to the right. Like I said, I don't know JVC, but I've seen that on other Japanese sets for sure. The service manual should have a voltage level to set it at (if it exists).

If not, then focus on the parts in the composite input circuit. Check voltages everywhere and compare against the service manual. If anything looks fishy, pull caps and check them.

Thanks! That gives me somewhere to start. I shared the service manual I have here. Based on the schematic on page 44 it looks like the composite signal goes straight into the IC, im not sure if their are any internal pots but I can get into it at some point and look.

There are over 100 adjustments that can be made via the service menu, but the service manual really isn't very descriptive on what they all actually do, outside of the standard geometry stuff unfortunately.

[Alex KL-1]

The "all-in-one" TV IC core can perhaps have different internal settings for each input, or simply the composite ones uses the comb filtering and that perhaps are not optimized (unlikely, but...)...
A lot of "perhaps" due to all these programmable IC's and it's features hidden for the users and even technicians; perhaps one bad choice for given model etc...

Difficult to pinpoit any direct culprit.

[vol.2]

You should also read this https://docs.google.com/document/d/1...it?usp=sharing

if you haven't before.

[BenM86]

Originally Posted by Alex KL-1

The "all-in-one" TV IC core can perhaps have different internal settings for each input, or simply the composite ones uses the comb filtering and that perhaps are not optimized (unlikely, but...)...
A lot of "perhaps" due to all these programmable IC's and it's features hidden for the users and even technicians; perhaps one bad choice for given model etc...

Difficult to pinpoit any direct culprit.

Originally Posted by vol.2

You should also read this https://docs.google.com/document/d/1...it?usp=sharing

if you haven't before.

Thanks! My particular model is a AV-32D302 with a Hitachi tube. And it uses the TB1253AN jungle chip and supposedly has a 3 line digital comb filter. I assume the comb filter is housed inside the jungle IC? Wonder if the IC has simply wore out.

[vol.2]

Originally Posted by BenM86

Wonder if the IC has simply wore out.

I seriously doubt it. It would be far more likely that some components somewhere are worn out or faulty.

Possibly it could have something to do with the settings, but I don't see how that could be true unless it was set wrong from the factory or someone has been in the settings and put something wrong. Normally it's setup correctly when it leaves the factory and the end-user doesn't have to mess with it.

It can be tempting to just try replacing a big IC because it seems like an easy thing to try, but it's very rarely the actual cause of failure in things like this.

When I have a big, difficult project like this, comparing voltages from the schematics is the number 1 way I make progress.

Doing this stuff can be really hard, and even after many years there are still some repairs I haven't figured out yet. It just be like that.

[BenM86]

Originally Posted by vol.2

I seriously doubt it. It would be far more likely that some components somewhere are worn out or faulty.

Possibly it could have something to do with the settings, but I don't see how that could be true unless it was set wrong from the factory or someone has been in the settings and put something wrong. Normally it's setup correctly when it leaves the factory and the end-user doesn't have to mess with it.

It can be tempting to just try replacing a big IC because it seems like an easy thing to try, but it's very rarely the actual cause of failure in things like this.

When I have a big, difficult project like this, comparing voltages from the schematics is the number 1 way I make progress.

Doing this stuff can be really hard, and even after many years there are still some repairs I haven't figured out yet. It just be like that.

I hear ya. It may end up being a juice not worth the squeeze situation. Overall the TV works almost perfectly. Probably easier to just find a S-VHS player with svideo out. The laserdisc is a little harder, good Elite units with good svideo out a super expensive. I may end up doing a recap one of these days just because and who knows that may help.

As far as the settings go, it's possible it's been messed with. D series TV's tend to trade hands often, so im sure the service menu has been accessed. The red push was already disabled when I got it, so someone has been in there at least once. I should at least sit down and make sure everything is set to factory based on the service manual just in case.

[vol.2]

Originally Posted by BenM86

As far as the settings go, it's possible it's been messed with. D series TV's tend to trade hands often, so im sure the service menu has been accessed. The red push was already disabled when I got it, so someone has been in there at least once. I should at least sit down and make sure everything is set to factory based on the service manual just in case.

I did have that thought. If you can do it safely, it's a good idea to make sure everything is correct. I wouldn't change any settings that aren't explicitly called out and explained in the service menu though; in my experience, many service menus contain options that are not documented for various reasons, and they shouldn't be messed with. Sometimes it has to do with some very basic operations that would never need to be changed, and sometimes they adjust things that weren't implemented in the circuit design (optional inputs and features).

There are absolutely settings in some service menus that will remove the picture, including the service menu text itself. If that happens, you're kind of screwed.

Again, I don't know JVC stuff too well, but I've run into it in other sets.

Recapping could help, but I'd recommend getting a good LCR meter (or an ESR meter if you want to save some money) and actually checking the caps you pull out rather than doing a shotgun. Sometimes shotgunning a set will end you up in worse shape than you started. This usually happens as a result of making mistakes (pulling up pads and traces, putting in caps backwards), but it can also happen because of less obvious mistakes such as using the wrong type of cap.

And that's why checking voltages is the way to go, because it points you to an issue in the operation of the circuit at a certain point. Once you discover a wrong voltage, you can scour the parts that would effect it and that should lead you to a problem. Sometimes there are multiple independent problems, or many problems caused by a cascade failure.

Whatever you're looking for seems like it's pretty specific though, because it's only on one input. Either the settings are wrong, or something touching only that input signal path is wrong. I like those chances.

But yeah, make sure the settings are correct first.

[BenM86]

Originally Posted by vol.2

I did have that thought. If you can do it safely, it's a good idea to make sure everything is correct. I wouldn't change any settings that aren't explicitly called out and explained in the service menu though; in my experience, many service menus contain options that are not documented for various reasons, and they shouldn't be messed with. Sometimes it has to do with some very basic operations that would never need to be changed, and sometimes they adjust things that weren't implemented in the circuit design (optional inputs and features).

There are absolutely settings in some service menus that will remove the picture, including the service menu text itself. If that happens, you're kind of screwed.

Again, I don't know JVC stuff too well, but I've run into it in other sets.

Recapping could help, but I'd recommend getting a good LCR meter (or an ESR meter if you want to save some money) and actually checking the caps you pull out rather than doing a shotgun. Sometimes shotgunning a set will end you up in worse shape than you started. This usually happens as a result of making mistakes (pulling up pads and traces, putting in caps backwards), but it can also happen because of less obvious mistakes such as using the wrong type of cap.

And that's why checking voltages is the way to go, because it points you to an issue in the operation of the circuit at a certain point. Once you discover a wrong voltage, you can scour the parts that would effect it and that should lead you to a problem. Sometimes there are multiple independent problems, or many problems caused by a cascade failure.

Whatever you're looking for seems like it's pretty specific though, because it's only on one input. Either the settings are wrong, or something touching only that input signal path is wrong. I like those chances.

But yeah, make sure the settings are correct first.

Well, the plot thickens. I have no idea why I didn't try this before. I went ahead and plugged the DVD player into the composite input which I had never done before, aaaand, its fine. So I guess there's nothing hardware wrong on the TV. I still dont understand why the issue is happening though.

Id be willing to believe the VCR and laserdisc are both just worn out, but then why don't they have the same artifacting on my other TV's? ill attach two comparison shots one with the episode 1 vhs and one with the episode 2 dvd. The vhs should of course be worse, but not THAT much worse. Same input, same settings on the TV and camera. And again, the VCR does not look this bad plugged into any of my hdtvs, just this one. Somehow im even more confused than I was before lol.