To watch this video it appears we'd need to join a cloud storage site. Sorry not interested in that.
Maybe you could post it on You Tube and take it down the video once the problem is solved.
You could also try to explain the issue.
Did you try swapping the Dynamics card with a good channel to make sure it's on the PCB.
Since the console was recently moved it could be a wire from a pot or switch.
If it follows the card.
The gate circuit is pretty simple. It looks like T3 does most of the work.
How is the Expander working. It's the same circuit.
C9 sets the attack timing and it's an electrolytic cap so it could be bad.
You can easily swap T3 and T4 from a working card. TR3 or TR4 maybe.
If I had to make a blind guess from experience my vote would be that C9 is bad.
If you change C9 and you don't have a 6.8uf you could try a 10uf as a test but for the
circuit to work correctly this cap needs to be the exact same valve.
Let us know how you make out.
