Thanks @techknight. Yes the online resources tell me 0000000F is software related, which confused me. But maybe NMI is being triggered somewhere, causing this error code to appear. I will check the NMI area carefully (which I haven't done yet apart from adding R11).
At this stage, I am assuming POST is successful (the fact initial boot chime sounds followed by the screen coming on and going to memory check) so it's either memory or NMI as you suggested.
Thank you @techknight for your reply.
The first photo was just to show what the board looked like when I got it. As part of repair, I cleaned up the area and added all of the missing components including R11. I don't believe NMI button is stuck because if I press it before the screen comes on, it goes to death chime straight away. So I know the button functions and it registers when I press it. However I will check the NMI traces again as you suggested.
I checked all traces from four Bank A RAM slots to RP6,7,8 and UL11,13,16,17 (74F573) yesterday using the schematic and they are all good so it doesn't look to be trace issues with SIMM slots. (BTW I found a mistake in the Bomarc IIfx schematic, SIMM slot data out pin should be 47, not 44. I found a couple more as well, which I can't recall right now)
So it looks like POST passes and it goes to RAM check and I thought it maybe failing there but with all SIMM slot traces looking good, that is not the case.
From various places I read that RAM check is the last check Mac does before showing the happy Mac screen. If RAM SIMM traces are all good, why would it fail? Could something between RAM SIMM and the memory controller be failing?
I am also going to hook up another Mac and see if I can use the diagnostic mode to get some more info. Never used a diagnostic mode before but hopefully I will figure out how to use it.
I added two more photos. One showing after cleaning up the damaged area and another showing after missing components added in (R11, D2, D3, R18)