I have +11v coming in to the D13 diode on the main board, but on the other side of that diode is have 0v. Also, and I assume this has to do with a bad diode, I don't have 18v on the other side of the 2 amp fuse, but the fuse is not blown.
I'm confused by this, are you saying you have +18v on one side of the fuse but not on the other? That sounds like a blown fuse? If you don't have +18V then you won't have 11V on the "channel" side of D13. The current flow is from the +18V, through the logic circuitry, through D13, and back
out to the +11V (it is a bit strange / confusing!). It isn't really 11V at all, it's a 7V supply hanging off the +18V.
If the +18V isn't there then as you say, everything on the +18V and +11V rails will be at 0V.
I don't think it's a problem with D13, it sounds like a problem with the fuse, or maybe the fuse solder joints or cracked tracks around the fuse.
I've attached the circuit diagram of the 611 fusing and diodes to help with this thread.
Thanks,
Andy