Opened up the Macintosh ED yesterday evening (haven't bothered "testing" it yet as I wanted to check it visually first). Was sold to me as "defective" anyway.

It's got a fair amount of dust inside, moderately greasy dust too! I will strip it down and clean it eventually...

On inspecting the analogue board, it visually has several broken solder joints on both J1 and J4. Easily repaired but I wonder if that's the cause for the crowbar though? Suppose it could be?

Will repair the solder joints tonight and report back...