JVC C-1320 Composite/S-Video Mod

[2thedawn]

Hey all, recently got an old 1990 JVC Master Command C-1320 from a friend and was looking for some help with it.
It's currently RF only and I'd like to add either composite or s-video inputs to it (for now; I think RGB is possible but I don't currently have anything that really hooks up to that...yet).
I've been tinkering around with it to little success, I am pretty new to this. Was just looking for some points on some things.

Here's some more info.
Set is a JVC C-1320 with a manufacture date of September 1990.
Can't seem to find a service manual or board diagram anywhere and am unaware of any similar models.
From what I've gathered there are a few standout ICs that I've been able to find datasheets for:
The Jungle/Chroma chip is a Toshiba TA8601BN.
The OSD chip is a Panasonic AN5352N.
The RF decoder/demodulator(?) chip is a Mitsubishi M51496P.

Now here is what I've tried so far.
Failed attempt #1 - Connect composite directly to Jungle chip
I wired the composite from my Genesis to Pin 34 on the TA8601BN (labelled Video IN on the diagram; assumed it would be a composite input or Luma of some kind)
I seem to be getting some black and white image but the sync isn't there.


Failed attempt #2 - Lift video out pins from RF IC and connect composite there
This one seemed a little more fruitful at first but quickly failed as well. I read from another post by a user here WOW90 (in this thread) whose set also had this RF chip.
They were able to composite mod theirs by lifting the video out and audio out pins from this IC and patching their composite in there. I decided to give that an attempt.
At first, it seemed I had colour and there weren't any sync issues.

However, after the logos during the game's intro where there is full-screen picture and colour, I began to experience sync issues and dropouts.

For reference, here's what its supposed to look like:


So yeah, that's where I am. Kinda stumped. Don't really wanna go any further just yet in fear of screwing things up but if anyone has any ideas on how to make this work or information on this set I should know, it's definitely welcome

[AilingSpice]

Hey all, recently got an old 1990 JVC Master Command C-1320 from a friend and was looking for some help with it.
It's currently RF only and I'd like to add either composite or s-video inputs to it (for now; I think RGB is possible but I don't currently have anything that really hooks up to that...yet).
I've been tinkering around with it to little success, I am pretty new to this. Was just looking for some points on some things.

Here's some more info.
Set is a JVC C-1320 with a manufacture date of September 1990.
Can't seem to find a service manual or board diagram anywhere and am unaware of any similar models.
From what I've gathered there are a few standout ICs that I've been able to find datasheets for:
The Jungle/Chroma chip is a Toshiba TA8601BN.
The OSD chip is a Panasonic AN5352N.
The RF decoder/demodulator(?) chip is a Mitsubishi M51496P.

Now here is what I've tried so far.
Failed attempt #1 - Connect composite directly to Jungle chip
I wired the composite from my Genesis to Pin 34 on the TA8601BN (labelled Video IN on the diagram; assumed it would be a composite input or Luma of some kind)
I seem to be getting some black and white image but the sync isn't there.


Failed attempt #2 - Lift video out pins from RF IC and connect composite there
This one seemed a little more fruitful at first but quickly failed as well. I read from another post by a user here WOW90 (in this thread) whose set also had this RF chip.
They were able to composite mod theirs by lifting the video out and audio out pins from this IC and patching their composite in there. I decided to give that an attempt.
At first, it seemed I had colour and there weren't any sync issues.

However, after the logos during the game's intro where there is full-screen picture and colour, I began to experience sync issues and dropouts.

For reference, here's what its supposed to look like:


So yeah, that's where I am. Kinda stumped. Don't really wanna go any further just yet in fear of screwing things up but if anyone has any ideas on how to make this work or information on this set I should know, it's definitely welcome

I’m know this is old and I don’t even know if OP is still active but I just wanted to ask about if this went any further because I have the same tv and wanted to try and’s mod it myself. Hoping it see this op but I’d anyone can help that be great!

[MacReady]

I have a JVC C-1328 which is very similar and the SAMs video troubleshooting section states "Inject a video signal at TP12 and check for video on the CRT". TP12 is a test pin on the PCB upstream of the jungle IC.

Regarding your Fail 1 attempt. Injecting composite to just the Video In is missing the Chroma and H/V Sync pins that are also on that jungle chip. Not sure why Attempt 2 is having issues but perhaps TP12 is a more stable injection point for signal.