No sync from C64 via RGB converter

[MagerValp]

I have an OSSC 1.6 that works great with my Amiga, but I’m having trouble getting a C64 to work. It’s hooked up via a JVC KM-V7EG S-Video to RGB converter, but the OSSC just says “NO SYNC”. I’ve tested the JVC RGB converter on a TV with SCART, and it works beautifully there. It also works with one of those cheap and cheerful SCART to HDMI converters, though it occasionally seems to drop sync. I coded a small test program to display gray bars and hooked it up through an S-video switch for testing so I can use my S-video monitor at the same time, and made some measurements with my pocket scope:

https://ibb.co/jjU9HT

[MagerValp]

The forum breaks the images links when I post them for some reason, so plain URLs here:

Setup: https://ibb.co/jjU9HT
-133 mV sync: https://ibb.co/ePg0P8
Luma: https://ibb.co/gvVGxT
64 µs scanline timing: https://ibb.co/kS6Zj8

[BuckoA51]

I’m not familiar with that transcoder, have you tried playing with Sync Analogue Sync Vth and Vsync Threshold under sync options?

[MagerValp]

Ah, good call! I nudged down the Vth from 123 to 112 mV and it recognizes it as 311p @ 50.27 Hz. After increasing H-PLL Pre-Coast to 4 and Post-Coast to 2 I get a good picture at 2x/3x/4x/5x ??

I get a pretty strong checkerboard pattern, so I’m ordering a LumaFix64 as well.

[trydowave]

MagerValp. I recently got the exact same transcoder as you but im having trouble with it. When i hook it up to my RGB scart theres a black diagonal band on the top left right hand corner. Over time it gets bigger and works its way down the screen and the picture starts to flicker and then finally after about 15 mins its blank. If i change my tv to YC though on the scart socket the picture is stable. Does yours do this? do u have a certain type of s video lead? any help would be greatly appreciated as i think ive brought a dub and they aint cheap. 🙁

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