JVC C-1320 Composite/S-Video Mod

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2thedawn
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Joined: Wed Sep 21, 2022 2:03 pm

JVC C-1320 Composite/S-Video Mod

Post by 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.
Image

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

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 :)
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