[Kenwood] trouble with autotuner on TS850

[WW3S]

My autotuner suddenly stopped working on 40m...all other bands ok but on 40
it appears to tune when the AT TUNE button is pushed but as soon as you
transmit, the SWR is high and power out is low. With the tuner out of line
and within the proper bandwidth for the antenna, everything is fine but as
soon as I engage the tuner I can't get a match. I'm not sure how the tuner
works but it's like something isn't latching when it should,