Requesting Advice on RGB Mod for JVC F-Series Multi-System

[joebliksem]

Hello everyone,

I am currently working on a project to perform an RGB mod on my JVC F-Series multi-system TV (model AV-F2983), and I could really use some expert advice from the community. I've been studying the circuit diagram for this TV, and I noticed that there is an unpopulated teletext portion of the board.

Before I proceed with the mod, I wanted to ask if anyone here has experience with this specific model and could help me understand whether it would be feasible to use the unpopulated teletext portion of the board to inject an analog RGB signal. I would greatly appreciate it if someone could take a look at the circuit diagram and give me some guidance. I've done a similar mod on a Trinitron but I can't find information on the F-Series, let alone using the text header.

Thank you in advance for your help and expertise. I'm looking forward to learning from your experiences and getting this RGB mod project off the ground!

Thanks

Joe

I've uploaded the circuit diagram here for reference:

Links to jungle chip datasheet and service manual for a similar model (I couldn't find the exact one, but this is the same chassis except this version has teletext populated)

https://drive.google.com/drive/folders/ ... sp=sharing

[joebliksem]

update: after scouring the forum, I noticed this that someone modded a NEC FS68v80.

By the looks of it, it's the exact same JVC chassis used in the F-series. Currently studying the mod.

https://shmups.system11.org/viewtopic.p ... start=2910

[joebliksem]

Hey

So I have cloned this mod precisely



Currently finding that replacing the bridging wire at R319 with a resistor results in no composite or RGB image. As soon as I remove the resistor, I'm able to revert to composite. Any ideas why it's not working? My understanding would be that, with no voltage applied to R319, the set should at least default to composite?



Thanks

[joebliksem]

Okay, I've now got got RGB working but cannot seem to get sync through S-Video. Can't get sync at all. What am I missing?

[KPackratt2k]

The reason why it's not syncing is the S-Video input is active only when a cable is physically plugged into the port as the inner shield of the S-Video connector is divided into two parts: a ground and a sensing circuit. When a cable is connected, the two shield pins are connected together, grounding the sense circuit to activate the input.

There are a few ways to work around this:

1. Connect an S-Video cable to the input to activate it.
2. Solder a jumper wire on the S-Video connector from the sense pin to the ground pin (usually the two pins for the shield). By doing this, the rear Composite video input will be disabled.
3. Run wires from the ground and sense pins of the S-Video connector to a switch. The best way to do this would be to replace your blanking switch with a double pole switch, wire blanking to the first pole and wire the S-Video sensing circuit to the second pole.

[joebliksem]

Thanks, I went for option 3 and it did the trick. In the end though, I found composite sync worked just fine and I already own the right cables.

Here's the working RGB mod for JVC F-Series / NEC FS68v80 with TB1227BN Jungle chip.

- Uses the analog RGB pins intended for teletext (not populated on the board)
- OSD works
- Bridging wire was present and removed where resistors were added.

[ NOTE ] I opted for RCA rather than Scart because it suits the RGBS cables I own, which have composite sync and audio jacks.

The reason why it's not syncing is the S-Video input is active only when a cable is physically plugged into the port as the inner shield of the S-Video connector is divided into two parts: a ground and a sensing circuit. When a cable is connected, the two shield pins are connected together, grounding the sense circuit to activate the input.

There are a few ways to work around this:

1. Connect an S-Video cable to the input to activate it.
2. Solder a jumper wire on the S-Video connector from the sense pin to the ground pin (usually the two pins for the shield). By doing this, the rear Composite video input will be disabled.
3. Run wires from the ground and sense pins of the S-Video connector to a switch. The best way to do this would be to replace your blanking switch with a double pole switch, wire blanking to the first pole and wire the S-Video sensing circuit to the second pole.