With some probing, D30, and D31 was broken between SCSI/SCC/ASC, and SWIM. This is surprisingly common becuase the bus junction/interconnect sits right below those 3 caps near the power molex plug.
But, not necessarily a show-stopper as far as booting and video issues. Sure you get no SCSI, Serial, or Sound. but itll still boot. Or, attempt to.
And there was the fact of bus contention. So I sat back and started thinking, the contention was happening randomly and sequentially. That rules out a hard failure because the contention would be there all the time and wouldnt go away. Even with or without ROM.
So that rules out a failed IC, So I was leaning more towards chip select/address bus because of the chip is talking, but at the wrong time.
Sure enough, A0 has a double break between ASC and GLU/CPU, and also to video muxes. A1 is broken between ASC and GLU. A0/A1 is used in the 030 for upper/lower addressing and bus sizing. VERY important! (24/32 bit addressing, and the 16-Bit UDS/LDS for the peripheral ICs.)
This allows the ASC addressing to float around. So it thinks its being addressed when its not. and presto, Contention. Plus, with A0 and A1 being missing on the video muxes, that explains the 24 pixels of jail bars, and 8 pixels of valid video data. 2 address wires can count to 3.
, and if you break down the video image in the posted picture above, you got 8 pixels of good data, and 24 pixels of bad data. Break it down into 8 pixel groups, well the count of 3 gets 24. That explains that.
What was throwing me off was I had open address lines before on the ASC with boards in the past, and everything was working fine. But the A0/A1 line is very important, and those are both open. First time I encountered that.
Now, to perform the repairs and hope it doesnt make an ass out of me. lol.