Hi all,
I've been working on a baby pac that I picked up earlier this year. I've successfully gotten the Vidiot board to boot, giving 10 flashes. I've also gotten the MPU to boot giving the 6 flashes. The harness on the mpu and vidiot board has been gone through, with new connectors and header pins. I'm not getting anything on the communications test at all, no numbers in either column. I'm getting continuity between the mpu and vidiot for all of the connectors. All three PIAs on the MPU/Vidiot have been tested, and were swapped anyways. Both U1 and U2 on the vidiot were removed tested, and swapped anyways. There aren't any stuck lines between the MPU and vidiot besides 5,6,15 (vidiot side) which are all control signals. Assuming that the Latch Input Data signal does what I think it does, the line is stuck high, and won't load data into the registers. I'm not sure where to troubleshoot next as these control signals are generated directly from the PIA (Assuming I read it correctly) Any helpful advice? and does anyone have a good explanation as to how the communication test actually works, which control signals are nessecary, and where the test starts from?

The manual is kind of vague when it talks about the control signals, but I did give it a reread.
All TTL/CMOS logic U1, U2, U3, U4, U5, U6, U35 have been socketed and replaced. I changed U20 on the MPU board as well. I did continuity checks, just to verify nothing was broken, and it checked out. Still at a loss where to go next

I already did continuity checks around the whole area on the vidiot board and mpu, didn't see anything broken.

I don't have another 6809, I'll have to order one. I changed the socket, and did continuity checks from the CPU to the surrounding areas and didn't notice anything.