Just now read this, but if you havenít already progressed too far on this, could you try this?
Have the chassis pulled and resting on an insulated work surface, look at the Item 23. . . the speaker. . . and note the ground connection, and find that wire and open that circuit in its making connection to chassis ground.
( It MIGHT just be soldered to the speaker frame, such that it is dependent on that speakers mechanical connection to the chassis proper )
Pull the mounting of the speaker to the chassis such that the speaker proper is now mechanically and electrically floating from chassis ground.
Power up ye olde radio and see if it will /is / now work(ing) ?
(No touchee-touchee speaker frame !)
73's de Edd