I have a 740 with no heat. This past weekend I dissembled the console enough to remove a radio a prior owner had installed, I also took this opportunity to examine the slider control which goes from cold (left) to warm (right) to see why it has no apparent effect.
The slider rotates an arm through an arc of perhaps 30 degrees, to the cold direction the last few degrees slide a cam on a vacuum switch, but other than that there's no apparent connection to anything else, i.e. a cable, rheostat or variable vacuum control. To the rear and bottom of the assembly there is a spot which looks like something had been mounted and removed. On the arm is a worn protrusion about 1/4 the way in from the side which looks like a cam may have been there and broken off.
I would appreciate at least a photo of what a normal functioning unit looks like on the bottom side as I expect a previous owner removed something here.
I've looked about for vacuum tubes, wires or cables which appear unconnected in the vicinity and haven't spotted anything which has placed me at wits end. Cooler days are coming and I'd very much like to get the heating working.
Thanks for any help!