I’ve got an old Quadra that mostly works, except for the looping/cycling on the first two EGs. It looks like they get stuck at EOC, and the next cycle never starts. What is most likely to be the cause? If it’s a bad IC, I’m reasonably handy with SMDs and I could replace it, but without a schematic I don’t even know where to start.
Do you have the expander connected? If it’s the case make sure all the connections are correctly done.
If you don’t have the expander, make sure you have all the jumpers installed.
I’ve tried it with and without the expander, and checked and reseated all the jumpers.
I’m sending it in today; hopefully they can figure it out without too much effort.
Hopefully it will get fixed. I remember something similar happened to me and I thought it was the case I had before (Pittsburgh Structure) that was the problem. I had a lot of weird power and grounding problems with that case.
I’ve got the same situation, except for it’s the fourth channel not looping or outputting EOC. Any update on how the repair went @the_laconic ? 
