yamaha cr-800

I have a very unusual problem with a yamaha cr800.  With an antenna installed and tuning to fm stations I can get signal pickup in fm mode.  But not in fm muting. so there is no stereo, afc/station or signal meter movement.  It is non responsive thru the entire fm scale.  There is not even a weak attempt at channel selection,  just dead.  I know the circuit and lights work because they were tested at a qualified tech shop in austin, texas and they work and pick up channels perfect but out in our rural location no such luck.  I have other receivers that work fine so our reception appears to be good.  This is really strange and the tech has no answers and has never seen this before.  Comments and suggestions would be greatly appreciated.