Just spent a frustrating few hours banging my head against the wall. I'll explain.
I know what the problem is with the dead ALT function on the 475A. See schematic. Q338 should have an Alt Trace Sync Pulse on it's base when the ALT switch is depressed. Nope. Flat line. In fact, by probing it I can make the trace on the CRT switch from channel 1 to 2. I tried following it back to the indicated R599 on the Switch Board. Can't find it. Why? Because the schematic for the Switch Board is missing from my Artek copy. Went on line to find other copies of 475A manuals. Missing from them too.
Went on Ebay to see if anyone had a hard copy manual. Nope. So I'm stuck.
The Switch Board is buried behind the channel attenuators and vertical board. I'm not about to go digging in there and ripping stuff out blind. What dumb luck.
So for now I buttoned up the 475A until I can find the missing documentation. Even though the alternate function is FUBAR the rest of the scope is OK so I put on the burn-in rack to accumulate some power on hours.