Can this TV be modded for S-Video?

[DatPhosphorGlow]

I absolutely love this thing but really need to get at least get S-Video out of it for it to be a keeper. It has a high resolution tube and the stereo sound coming out of it is AMAZING. The tube is like new and I even scored a new old stock remote off ebay for it. If I can get S-Video out of this TV it would be my end game CRT.

She's a JVC AV-20CM4 and here is a link to a PDF service manual with the board schematics. https://pdfslide.net/documents/av20bm4- ... tml?page=1

I only play PSX, and the composite video output just isn't cutting it for the graphics the console is capable of outputting. Had some fellow users already look over the board diagrams and doesn't look like it can be modded for RGB.

I'm quite handy with an iron, pcbs, and components, but when it comes to technicalities of electrical engineering I'm pretty lost. Absolutely no problem drilling a hole in the back for an S-Video port. Have an iron, multimeter, power supply and all that good stuff so can report back as instructed for error diagnosis. No oscilloscope though.

Any help/advice greatly appreciated!

Blurry cell phone pictures for your viewing pleasure (composite video):

[KPackratt2k]

Looking at the datasheet for the jungle chip, it appears the Chroma input (Pin 43) can take either a low voltage band-pass filter signal from a standard S-Video Chroma output (0.3V) or a high voltage take-off filter signal (6.0V in this case) from a VIF output (coming from the AV switch IC in this case).

Run S-Video Luma (Pin 3) into the Composite video input.

For Chroma, lift R314 and C313 near pin 43 of IC101 (the TA8725AN jungle chip), then inject Chroma through a coupling capacitor (between 0.01uF (10nF) and 0.1uF (100nF)).

If you wish to preserve Composite/RF functionality, you can tie the lifted component pins together and run a SPDT switch in the following setup:
Switch Left: R314 and C313 legs (Composite/RF output)
Switch Center: IC101 Pin 43 (Jungle Chroma input)
Switch Right: S-Video Pin 4 (S-Video Chroma output)

Let me know if this works or if you experience problems with this setup.

[DatPhosphorGlow]

Thanks for the help Kpackratt2k.

Should be able to do some testing later tonight. Hopefully I have a "coupling capacitor" in that range on one of my scrap donor boards. Just recently moved, hopefully I can find my box of donor boards.

Does the Chroma ground matter at all or is the ground shared with luma? No need to inject the Chroma ground?

[DatPhosphorGlow]

Okay, no luck finding my box of scrap boards but cracked open a faulty surge protector I had lying around and found one of these. It's rated for "10NF 50V" according to this supplier: https://katodo.com/it/condensatori/666- ... adial.html

I'm assuming them capitalizing the N in the nanfarod abbreviation is a typo and that doesn't mean anything?

This should work right?

[KPackratt2k]

You can ground both grounds (Pins 1 and 2, and the shield) at the same place. I'd ground it at the same place as the AV jack ground for convenience when wiring it.

That capacitor should work fine.

[DatPhosphorGlow]

First attempt unsuccessful.

I got a black and white overly bright image. Sony boot logo was deformed and offset. When PlayStation logo displayed area of screen wouldn't sit still in area as pictured. Flyback was going crazy with the whining on that screen. Didn't want to push console to boot further with the TV behaving that way.

I did not use any fancy shielded cable or anything like that just to see if I can get the ball rolling first. Used some random 30AWG wire for the jumper from pin 43 of IC101, and then some hacked alligator clip from the 10nF cap to the S-Video breakout cable I have.

The breakout cable is good, I use it all the time with my Commodore 1702.

Lifted C313 and R314 on path in between C313 and R314.

Where did I go wrong?

[KPackratt2k]

It looks like you've soldered Chroma into the wrong pin. You're currently sending it to Pin 33 which is Horizontal Output, hence the weird distortion. You want to solder it to the pin marked in red in this diagram:



Count the pins on the IC until you find the correct one, then move the wire to the correct pin once you've identified it.

[DatPhosphorGlow]

Lol, can't believe I got the wrong pin. I actually counted 3 or 4 times to be sure I had the right pin. Turns out I inverted the pin number in my head.

I actually have it soldered to pin 34 in that picture, instead of pin 43. I have a tendency to do that with numbers.

Will report back after I fix that mistake!

Thanks for checking my work, appreciate it.