S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

[Derf]

So, it looks like this set is not RGB moddable, but I saw there's a Chroma input, so I thought to try connecting C to Pin 36 on Jungle (Chroma In, 75ohm to ground and coupling capacitor on the motherboard) and the composite port for Y. No luck or image at all.

Any ideas on where to go from here? Perhaps that AV switch (Pin 43) is used to switch between svideo and composite on the jungle?

I couldn't find a clear datasheet for this jungle, but the crappy photo I could find does seem to line up pinwise with the LA7673 below.

[BazookaBen]

Possibly. My next step would be to look for other TVs with the same jungle chip that have s-video and see how it's wired up

[Derf]

Possibly. My next step would be to look for other TVs with the same jungle chip that have s-video and see how it's wired up

I can't seem to find much about that jungle or what other sets used it. I realized I had typed the wrong jungle IC in the title, so I've fixed that now.

[vol.2]

Possibly. My next step would be to look for other TVs with the same jungle chip that have s-video and see how it's wired up

I can't seem to find much about that jungle or what other sets used it. I realized I had typed the wrong jungle IC in the title, so I've fixed that now.

The datasheet is available, and it says that S-Video is supported in the features section. It doesn't give a really clear path to that though; the example schematic is a normal composite video setup.

https://www.alldatasheet.com/datasheet- ... A7672.html

Did you get anywhere with it?

[Derf]

Possibly. My next step would be to look for other TVs with the same jungle chip that have s-video and see how it's wired up

I can't seem to find much about that jungle or what other sets used it. I realized I had typed the wrong jungle IC in the title, so I've fixed that now.

The datasheet is available, and it says that S-Video is supported in the features section. It doesn't give a really clear path to that though; the example schematic is a normal composite video setup.

https://www.alldatasheet.com/datasheet- ... A7672.html

Did you get anywhere with it?

Nope, no luck. I tried sending Chroma to the Chroma In pin (Pin 36) and Y through composite port, and I also tried isolating the Chroma In pin from the rest of the circuit, no luck. I get black and white input from Y, but no color.

[vol.2]

Nope, no luck. I tried sending Chroma to the Chroma In pin (Pin 36) and Y through composite port, and I also tried isolating the Chroma In pin from the rest of the circuit, no luck. I get black and white input from Y, but no color.

I think what's going on is that the composite signal gets push through discrete components to get demodulated. If you look at the sample schematic, the external composite gets input through pin 40 and then it just goes through an internal switch that selects either the internally demodulated RF signal, or the ext composite signal, and then it passes it right back out of the chip to some external components to separate the chroma, luma, and sync, and is then passed back into the chip through multiple pins.

The datasheet explicitly mentions S-Video input capabilities, it just doesn't give an example circuit for it. It might be possible to figure it out by comparing the 9PT40 schematic and the datasheet, but I'm not sure.

[Derf]

Nope, no luck. I tried sending Chroma to the Chroma In pin (Pin 36) and Y through composite port, and I also tried isolating the Chroma In pin from the rest of the circuit, no luck. I get black and white input from Y, but no color.

I think what's going on is that the composite signal gets push through discrete components to get demodulated. If you look at the sample schematic, the external composite gets input through pin 40 and then it just goes through an internal switch that selects either the internally demodulated RF signal, or the ext composite signal, and then it passes it right back out of the chip to some external components to separate the chroma, luma, and sync, and is then passed back into the chip through multiple pins.

The datasheet explicitly mentions S-Video input capabilities, it just doesn't give an example circuit for it. It might be possible to figure it out by comparing the 9PT40 schematic and the datasheet, but I'm not sure.

Messed around with it more tonight. Thought maybe it just detects composite input and turns off Chroma pin processing so I tried bypassing Y straight to pin 34, but then Luma isn't even displayed. Also tried toggling pin 43 (AV switch) but that just changes it to the antenna input snow screen.

Seems that no matter what I do, it ignores Chroma input.

[vol.2]

Messed around with it more tonight. Thought maybe it just detects composite input and turns off Chroma pin processing so I tried bypassing Y straight to pin 34, but then Luma isn't even displayed. Also tried toggling pin 43 (AV switch) but that just changes it to the antenna input snow screen.

Seems that no matter what I do, it ignores Chroma input.

Yeah, that makes sense. If you follow the block diagram, the whole A/V switch area is just to toggle between the video from the IF section and the external composite input. The result of that is passed directly out of the chip on pin 38 and broken down into multiple signals with discrete components. The only way to do it is to reverse engineer the various inputs downstream from there. It looks like it ties directly into the chip at 29 (H/V), 31 (brightness clamp), 33 (videotone, seems to effect the sharpness and contrast), 34 (black expand, something like luma?), and 36 (chroma). I'm going to go out on a limb and say that the voltages might be different (from standard chroma), and some kind of DC restoration would be necessary to bring the chroma to the to correct offset. Maybe someone else here with more experience can comment. Best possible situation is to find a set with s-video that uses this chip and copy the circuit. Something from the early 90s most likely

[Derf]

Messed around with it more tonight. Thought maybe it just detects composite input and turns off Chroma pin processing so I tried bypassing Y straight to pin 34, but then Luma isn't even displayed. Also tried toggling pin 43 (AV switch) but that just changes it to the antenna input snow screen.

Seems that no matter what I do, it ignores Chroma input.

Yeah, that makes sense. If you follow the block diagram, the whole A/V switch area is just to toggle between the video from the IF section and the external composite input. The result of that is passed directly out of the chip on pin 38 and broken down into multiple signals with discrete components. The only way to do it is to reverse engineer the various inputs downstream from there. It looks like it ties directly into the chip at 29 (H/V), 31 (brightness clamp), 33 (videotone, seems to effect the sharpness and contrast), 34 (black expand, something like luma?), and 36 (chroma). I'm going to go out on a limb and say that the voltages might be different (from standard chroma), and some kind of DC restoration would be necessary to bring the chroma to the to correct offset. Maybe someone else here with more experience can comment. Best possible situation is to find a set with s-video that uses this chip and copy the circuit. Something from the early 90s most likely

Current best guess (after LukeEvansSimon suggested it) is that it's the "chroma killer" (ACC killer) of the set turning off color processing if it doesn't see a chroma signal coming in through the regular composite port. No idea how to disable it though. There's a "Chroma VCC" pin on it that sits at 8.9V, but it's also connected to other stuff and the voltage doesn't change if I run a composite signal, just luma, or have nothing connected.

[vol.2]

Messed around with it more tonight. Thought maybe it just detects composite input and turns off Chroma pin processing so I tried bypassing Y straight to pin 34, but then Luma isn't even displayed. Also tried toggling pin 43 (AV switch) but that just changes it to the antenna input snow screen.

Seems that no matter what I do, it ignores Chroma input.

Yeah, that makes sense. If you follow the block diagram, the whole A/V switch area is just to toggle between the video from the IF section and the external composite input. The result of that is passed directly out of the chip on pin 38 and broken down into multiple signals with discrete components. The only way to do it is to reverse engineer the various inputs downstream from there. It looks like it ties directly into the chip at 29 (H/V), 31 (brightness clamp), 33 (videotone, seems to effect the sharpness and contrast), 34 (black expand, something like luma?), and 36 (chroma). I'm going to go out on a limb and say that the voltages might be different (from standard chroma), and some kind of DC restoration would be necessary to bring the chroma to the to correct offset. Maybe someone else here with more experience can comment. Best possible situation is to find a set with s-video that uses this chip and copy the circuit. Something from the early 90s most likely

Current best guess (after LukeEvansSimon suggested it) is that it's the "chroma killer" (ACC killer) of the set turning off color processing if it doesn't see a chroma signal coming in through the regular composite port. No idea how to disable it though. There's a "Chroma VCC" pin on it that sits at 8.9V, but it's also connected to other stuff and the voltage doesn't change if I run a composite signal, just luma, or have nothing connected.

That's easy enough to test. You could pump a regular composite video signal in while isolating the chroma pin and sending that separately. Any console that has both composite and s-video on the output would work. If it display something in that configuration, that's what's happening (probably)

But again, if you look at the schematic, it derives all those other signals from the composite video. Whatever implementation of s-video is done has to replicate all of the other signals. Look at the block diagram:

[KPackratt2k]

I managed to find a service manual for a set that uses the same jungle chip as this one, but has an S-Video input. Maybe analyzing its schematics and attempting to copy it in a way could help?

https://www.manualslib.com/manual/75897 ... 26201.html

[Derf]

I managed to find a service manual for a set that uses the same jungle chip as this one, but has an S-Video input. Maybe analyzing its schematics and attempting to copy it in a way could help?

https://www.manualslib.com/manual/75897 ... 26201.html

Took a look, it's definitely past my abilities. Good find!

[vol.2]

I managed to find a service manual for a set that uses the same jungle chip as this one, but has an S-Video input. Maybe analyzing its schematics and attempting to copy it in a way could help?

https://www.manualslib.com/manual/75897 ... 26201.html

I might be able to do something with this, but I'm crazy busy at work right now. Thanks for posting this, I think it's going to be very helpful.

[KPackratt2k]

A couple weeks ago, I've gotten around to S-Video modding my Sony KV-9PT20 (the black version of the 9PT40) and made note of the process.

- The Chroma pin on the LA7672 jungle chip is wired to both the Chroma buffer (which grabs Chroma from the Composite video signal) and the Color control knob. Likewise, the schematic for the Mitsubishi TV I referenced earlier has its jungle chip Chroma pin wired to both a Chroma switching IC (which toggles between a comb filter Chroma output for Composite/RF and the S-Video Chroma pin) and a D/A converter that handles picture controls. In order for the Chroma input of the chip to function, it must be wired to both a Chroma input and a Color control circuit. You can't just inject Chroma by itself into it.

- There's a trap filter on the Luma side of the buffer circuit that can reduce the image resolution by filtering out the 3.58 MHz band of the signal. For the S-Video mod, you would ideally want to remove that filter and wire it to a switch so that it's only active when the set is in Composite mode.

With those details out of the way, here's a successful mod circuit for this chassis:

Spoiler

The gist of it:
- Remove the SMD 0.01 uF coupling capacitor (C221) between the Chroma buffer circuit and the Chroma pin (36) of the LA7672 jungle chip, this will disconnect the Composite/RF Chroma signal from the chip while preserving the required Color control circuit.

- Remove LC201 from the Luma circuit (either lift it out of the pin connected to R252 or remove it and locate it elsewhere on the board with one leg connected to Ground) and wire it to the Composite video side on the first pole of a DPDT switch. The original pad where LC301 used to be connected should go to the center leg of your switch and the lifted leg of LC301 should go to the right leg of the switch.

- Connect the Chroma pin (36) of the jungle chip to the center leg on the second pole of your switch through a 0.01uF ceramic capacitor, connect the Chroma pin of your S-Video connector to the left leg of the switch and connect the Chroma buffer circuit to the right leg of the switch. You should place a 75 ohm grounding resistor on the Chroma pin of your S-Video connector, as the colors will look off without it.

- Luma should be connected to the Composite Video input pin and the Ground pins of your S-Video connector should go to a nearby Ground on the chassis (One of the Ground pins of the RCA jacks on the back of the set should be a perfect spot).

If done correctly, you should get a nice clear vibrant image on your 9" Trinitron when your switch is in S-Video mode and you have a device plugged into the S-Video input.

[vol.2]

A couple weeks ago, I've gotten around to S-Video modding my Sony KV-9PT20 (the black version of the 9PT40) and made note of the process.

- The Chroma pin on the LA7672 jungle chip is wired to both the Chroma buffer (which grabs Chroma from the Composite video signal) and the Color control knob. Likewise, the schematic for the Mitsubishi TV I referenced earlier has its jungle chip Chroma pin wired to both a Chroma switching IC (which toggles between a comb filter Chroma output for Composite/RF and the S-Video Chroma pin) and a D/A converter that handles picture controls. In order for the Chroma input of the chip to function, it must be wired to both a Chroma input and a Color control circuit. You can't just inject Chroma by itself into it.

- There's a trap filter on the Luma side of the buffer circuit that can reduce the image resolution by filtering out the 3.58 MHz band of the signal. For the S-Video mod, you would ideally want to remove that filter and wire it to a switch so that it's only active when the set is in Composite mode.

With those details out of the way, here's a successful mod circuit for this chassis:

Spoiler

The gist of it:
- Remove the SMD 0.01 uF coupling capacitor (C221) between the Chroma buffer circuit and the Chroma pin (36) of the LA7672 jungle chip, this will disconnect the Composite/RF Chroma signal from the chip while preserving the required Color control circuit.

- Remove LC301 from the Luma circuit (either lift it out of the pin connected to R252 or remove it and locate it elsewhere on the board with one leg connected to Ground) and wire it to the Composite video side on the first pole of a DPDT switch. The original pad where LC301 used to be connected should go to the center leg of your switch and the lifted leg of LC301 should go to the right leg of the switch.

- Connect the Chroma pin (36) of the jungle chip to the center leg on the second pole of your switch through a 0.01uF ceramic capacitor, connect the Chroma pin of your S-Video connector to the left leg of the switch and connect the Chroma buffer circuit to the right leg of the switch. You should place a 75 ohm grounding resistor on the Chroma pin of your S-Video connector, as the colors will look off without it.

- Luma should be connected to the Composite Video input pin and the Ground pins of your S-Video connector should go to a nearby Ground on the chassis (One of the Ground pins of the RCA jacks on the back of the set should be a perfect spot).

If done correctly, you should get a nice clear vibrant image on your 9" Trinitron when your switch is in S-Video mode and you have a device plugged into the S-Video input.

Hell yeah. Thanks so much for doing the legwork and writing it up. I'm will definitely have a go at my KV-9PT20 when I have some more time.

[vol.2]

Ok. I have also completed the S-Video Mod on my KV-9PT20.

I'd like to note that I'm seeing a very faint Horizontal ringing artifact (Vertical lines spaced about 1 cm apart) on a specific brightness value. It doesn't effect all brightness values equally, just about idk maybe 40 IRE.

It's not distractingly visible, and is basically only apparent when the whole screen is a single value, so it's not a deal killer or anything. It's still waaaay better over S-Video than it ever was over composite.

My guess with the ringing is that it has something to do with the value of the input capacitor on the Chroma input on the Jungle IC and/or impedance matching issues.

[TheRetroCarrot]

I had some spare time last night and gave this mod a go. Unfortunately something on the luma side is causing me major issues. Wired everything as referenced in the schematic prior, seemed to get chroma but no luma/sync on either composite or s-video. Restored to stock and still the same issue on composite now... Very strange, had no odd soldering or handling mishaps, can't find any obvious components that were near my working areas.

Kinda sad, no idea where to go from here for troubleshooting. I feel like I'm overlooking something very obvious, but it's such a simple mod and barely anything on the board needed touching.

[vol.2]

Kinda sad, no idea where to go from here for troubleshooting. I feel like I'm overlooking something very obvious, but it's such a simple mod and barely anything on the board needed touching.

Hmmmm. Well, the very small capacitor on pin 36 is easy to mess up, and that area is super tight, so you could easily bridge something.

Also, if you haven't already, I would reflow the solder joints on the AV input and the surrounding area on the PCB. Broken solder joints often do not look broken to the naked eye.

[TheRetroCarrot]

I can see operating voltage through pins 36/40/34, the 0.01uf cap, etc with a source plugged in via composite. The filter capacitor is removed at the moment (I broke it haha), but shouldn't effect the ability to at least get sync especially on s-video I would think.

I'm worried something in the jungle fried, but I don't see how, it's such a straight forward mod when it comes to the actual application.

[TheRetroCarrot]

Swapped the filter cap, as well as the 0.01uf cap and restored everything to stock specs. Made no difference, chroma is all good, red and blue signal with no sync on composite, same thing if I temporarily rig in an s-video jack. Reflowed half the board at this point with no change, have voltage all the way from the composite plug to the neck board on Y. Kinda bummed about this, I was extremely happy to finally find a small set like this locally. I have a friend who is significantly more knowledgeable than myself who will help out when he has a chance. In the meantime if anyone has things to troubleshoot I'm happy to try so I can save him the headache.

[TheRetroCarrot]

Can someone tell me if this majestic factory capacitor/resistor setup is normal? Or was this possibly an as needed repair they did. It's clearly done in the factory as it's the same glue used up top and for purity rings, tube placement, etc.

(I know my filter cap should be film, this is temporary)

Edit: I found my issue for luma, it was a jumper with a cracked solder joint. I have sync and image again but am missing red it appears. The hue and color adjustment seems to work, but red is just black and white when cranked fully in that direction. Getting there...

Edit 2: My red died from another poor solder joint on the neckboard, if it shifted at all it was gone. Reflowed the board and it's good to go. The mod was a success. I can't detect the ringing artifact mentioned at all, that being said it is much too sharp, I'll have to check the service manual if there's any adjustment for that. Overall it looks really good, very happy with it. Pro-tip a ceramic capacitor cannot be used in place of a polyester film capacitor for a trap filter lol, it looks so bad when that's in circuit, I'll put the correct one in when it arrives.

Thanks for the tips, schematic, and explanation! Still curious if other people who've opened these sets have that mess of a capacitor under the board though haha.

[vol.2]

Can someone tell me if this majestic factory capacitor/resistor setup is normal? Or was this possibly an as needed repair they did. It's clearly done in the factory as it's the same glue used up top and for purity rings, tube placement, etc.

Yes, that bodge cap is on my set as well. It's factory.

I'm glad you found the problem. I was very confident it would be solder joints; 30 year old solder can just break and you can't always see it. It's a very common "wtf" source because it tends to happen when we rip out boards to do stuff like this.

If you have time, you might check the ringing issue I mentioned by using HCFR and looking at 40 IRE across the whole screen. 240p Test Suite has all the HCFR slides.

that being said it is much too sharp

No. It might have a sharpness circuit, but I haven't looked into that yet. If it does, it's always on. There's a procedure for removing it from the circuit, but I've never done it, and I'm not sure if it works on all Sonys

Okay, looking at the schematics, I'm fairly certain that Sony just chose a permanent value for the Sharpness on this design and called it a day. I made a post asking for ideas on how to add a sharpness control or to turn it off.

I think actually there are plenty of other sets with this Jungle IC, so we can probably find one that has a Sharpness control and copy the circuit.

[KPackratt2k]

Can someone tell me if this majestic factory capacitor/resistor setup is normal? Or was this possibly an as needed repair they did. It's clearly done in the factory as it's the same glue used up top and for purity rings, tube placement, etc.

Mine has the same thing too, I'm guessing there was something that Sony forgot to add to the PCB schematic, so they ended up bodging it onto the board at the factory rather than redo the PCBs for the set, to reduce waste and costs.

While you're in there, I'd recommend reflowing the solder joints on the power supply just to be safe. Mine had an issue where the set would flicker on and off at times and it turned out to be a faulty joint on the power supply.

[TheRetroCarrot]

I actually kind of like the overly sharp image on this set due to the size, I've only tested a couple games but they all looked good. It's just in test patterns it shows a very oversharp image, lots of halos, not sure I'd be concerned enough to do anything about it.

The jumper I found was actually an odd one, it wasn't really a bad solder joint, I tested basically every component near where I was working on since I was reflowing nearby as I went, never bothered to check jumpers before and noticed no connectivity through one. I cleaned up the pad on one end and was greeted by nothing, the jumper itself was cut short and only went about halfway through the board. When I reflowed, the weak contact it must of had was no longer made. I ended up just replacing the jumper and installing it through the board properly.

I've reflowed probably 75% of the board at this point. Might as well do the power section while at it. The neckboard all looked visually perfect, but clearly wasn't, that's all reflowed completely.