[Kenwood] TS-850SAT won't stop scanning

[Walter Miller, AJ6T]

My old reliable TS-850SAT has suddenly come up with a problem related to 
scanning.  The rig now scans frequency continuously, and the only way I 
can stop it is by pressing the F.LOCK button or by pressing and holding 
the SCAN button.  Resetting the microprocessor by powering up with the 
A=B button pressed does not help.  In that case the rig wakes up at 
14.000 MHz and immediately starts to scan upward in frequency.  The main 
tuning knob also changes the frequency, but the scan continues.  The 
radio receives and transmits normally at whatever frequency was on the 
display when the F.LOCK button is pressed.  When the F.LOCK button is 
pressed again (or the SCAN button is released), the scanning resumes.

Any suggestions?

73, Walt, AJ6T