I think the HAS 3.1 is just using the default settings, other than the controller mappings that I set. It's outputting via SCART to the OSSC, and I've tried plugging headphones into the 3.5mm jack on the HAS, but I'm still not getting any audio going that route, either. The OSSC is set to Line5x mode; haven't tried switching to line2x or anything a little more lenient. The weird thing is that there's no audio or video, though - I could understand the OSSC having video issues but still outputting sound... but nothing? Just kinda weird. The board was working fine before the seller sent it, and it was well-packed... so that, combined with the fact that the board is getting power has me pretty confused as to what's happening.
All other JAMMA boards I have work fine with these settings. Cave stuff, CPS-2 stuff, ZN-2 stuff, etc.
This really doesn't tell much, because the HAS settings could have changed during shipping or during case assembly, it's been almost two years?When you say you don't get audio, have you also tried to plug in the headphones or speakers to the HAS' 3.5mm jack output? If not, please do it, wait a moment for the attract mode sounds (unless it's disabled, then add coins instead).
I used to own a Mr Driller 2 PCB and also know people who own it and it works just fine,
however not sure if it's compatible with the OSSC (it should be, though - try changing H-PLL pre and post coast settings).
edit: The most important question that I should have asked earlier - does the OSSC lock the signal (the OSSC's LCD screen should display the refresh rate of the signal)? If it does, but you don't see anything on the screen, then it's a problem with your TV set.