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

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

Post by 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.

Image
Last edited by Derf on Sun Jan 15, 2023 7:01 pm, edited 1 time in total.
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BazookaBen
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by 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
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by Derf »

BazookaBen wrote: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.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by vol.2 »

Derf wrote:
BazookaBen wrote: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
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by Derf »

vol.2 wrote:
Derf wrote:
BazookaBen wrote: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.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by vol.2 »

Derf wrote: 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.

Image
Derf
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by Derf »

vol.2 wrote:
Derf wrote: 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.

Image
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.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by vol.2 »

Derf wrote:
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
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by Derf »

vol.2 wrote:
Derf wrote:
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.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Toshiba TA1242N Jungle)

Post by vol.2 »

Derf wrote:
vol.2 wrote:
Derf wrote:
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:

Image
KPackratt2k
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by 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
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by Derf »

KPackratt2k wrote: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!
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by vol.2 »

KPackratt2k wrote: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.
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by 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
Image
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.
Last edited by KPackratt2k on Mon Feb 05, 2024 6:45 pm, edited 1 time in total.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by vol.2 »

KPackratt2k wrote: Fri Sep 15, 2023 1:44 am 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
Image
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.
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vol.2
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Re: S-video mod for Sony KV-9PT40 (Sanyo LA7672 Jungle)

Post by 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.
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