Ah sorry about delay, I am not online that often anymore… Anyways, I’d like to add to BuckoA51’s answer that at least my Amiga 600 seems to put out quite dirty and/or weak sync signals and the OSSC has troubles to sync to anything else than standard PAL no matter what LPF settings. Or perhaps Amiga goes to gensync mode, dunno. This happened with both SCART and VGA inputs.
This was fixed by using simple DIY buffered VGA adapter. I used schmitt trigger, that should clean dirty signal a bit more than just a simple buffer. Please notice that this is no fault in the OSSC since you are *supposed* to use buffered adapter with Amiga in any case (due to Amiga going to gensync mode if RGB output is loaded too much).