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.

[Author]

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