Jens-as recommended, here is a new thread.
Received MK3 and tried installing this week in an NTSC A1200 rev 1D system with 3.1.4 ROMs. Only expansion is a Kipper SDE+ RAM board (which has been removed for isolation).
I have tested both VGA and HDMI outputs with different cables. I've run the VGA output to an OSSC, which does not detect any signal activity. Lisa has been scrubbed with scratch brush and wiped with IPA. Multiple re-seats of both CIA and LISA boards (appears to be latching well).
If there are test points for troubleshooting with a VM, that would help.
Cheers for the support.