Remove bottom cover, and the 1/4 inch hex bolts are visible at either end of the mesh cover(s). While in there, you may as well touch up solder joints under EVERY Molex connector that is PC board mounted. (very common failure in a 35+ year old unit).
When refurbishing old solder, remove some of the joint with a solder sucker, apply rosin flux and replace the now missing solder with a new flow heating both surfaces to the same melting point so the solder melts on BOTH surfaces to be joined.
When refurbishing old solder, remove some of the joint with a solder sucker, apply rosin flux and replace the now missing solder with a new flow heating both surfaces to the same melting point so the solder melts on BOTH surfaces to be joined.