Hey georgehifi

Do you still have the S500II schematic or repair manual?  I could use it.  Mine is bone-stock, never been touched (except by the factory within the first year of it's life to repair physical damage from clumsy movers).  It probably needs "touched" now.
I’ve got S300 II which is the same but for higher rails and more outputs.
S500 circuit
And bias procedures for all. and more stuff on both, it's a total of 15mB so wait for it. 

I’ll email them to you, if anyone else wants them can you pass them on.

PM me with you email.

Cheers George
Looks like Agone doesn't have PM available. Just post your email here if you can't PM me.

Cheers George