Technics SL-7 Turntable No Audio

Greetings. My Technics SL-7 turntable has been with us since 1980s. It always worked perfectly until the other day.
Without warning there was no audio.
Mechanically  everything seems to work normally. All buttons respond as usual. The tone arm drops, tracks and returns as always. 
I do hear the clicks off the tone arm switches and muting relay.
 The receiver has been checked ok with a known working turntable.
The ortofan cartridge and stylus were swapped with known working parts.
The wiring harness to the cartridge as well as the two audio cables check ok with the ohm meter.
Everything looks ok on the pcb boards, All removable harness plugs have been pulled then cleaned.
The only thing I notice is a faint  electrical odor but nothing appears to be burned.

Any advice would be appreciated  
Thanks, William J