It's probably NOT what the problem is, but i they need to be ruled out as a cause.
Clean the variable capacitor (tuning cap). Use a "NON-RESIDUE" electronics cleaner. CRC QD Electronics cleaner is avail. @ Home Depot for about $8.00 a can. You spray all the fins while moving the dial knob back and forth. Then blow dry with a hair drier set to COOL and HI SPEED. Once done, Take some DeOxit, spray some into the cap and dip the straw into it. Close off the open end with a finger and move it to the clips that keep the shaft of the capacitor attached to the frame. Drip a drop on each clip and the brass clips at the ends. Then exercise the knob back and forth full run 20-25 times. DO NOT GET DE-OXIT on the fins. If you do, LIBERALLY FLUSH Them with the CRC AGAIN! LET dry thoroughly (24 hours). Power up the unit and check again.
Also clean FM MUTING SWITCH, and the SELECTOR SWITCH. Have you tried FM in BOTHthe FM MONO position and FM AUTO position??
On the AWE-015 (AM/FM tuner Board) check the FM B+ @ PIN 20 and PIN 5 on the FM FRONT END (Box with the Tuning Cap). (Selector in FM MONO or FM AUTO). These get power from PIN 7 of the AWE-015 board and thru the selector switch section 3 rear @ pins 1 & 2. Section wafers are counted from the front of the unit to the back.
AM gets B+ @ PIN16 which is fed from Pin 7 when the Selector is in the AM position. PIN 4 is the MAIN INCOMING B+ from the Power Supply (AWR-011) Pin 2 @ 12.5VDC.
Also check the ground from PIN's 2 & 23 on the AWE-015 board. Make sure the chassis and ground lead is clean, shiny, and tight!
