Has anyone fitted a Modbo 750 to a Pal 79003? I've messed around for hours now with one that works intermittently

When it boots it boots fine everytime, but from cold its takes 3-4 resets to actually boot (gives me black screen).
Done all the obvious stuff, uninstalled/reinstalled repositioned the chip etc etc but this is doing my head in now. I know the chip works because it does boot, I just need to resolve the unreliable boot rate.