[Yaesu] FT-990 Folds Back Power on 40M

[w1nk at cox.net]

This has me truly puzzled....

Last night and tonite during the CQWW RTTY contest, I noticed that my FT-990 is folding back power only on 40M RTTY.  I've watched my watt meter indicate 50, then 40 then 30 watts out.  Switch to CW, 100 W out.

Any other band is fine...100W out on RTTY (or any other mode for that matter).

The rig is running cool to the touch, the fan is kicking in appropriately... so I assume heat is not an issue.
 
Operating time seems to be a factor....in other words, prior to switching to 40 I had been on 20 for about an hour or so.  This morning after the rig had "rested" overnight, I had 100W out on 40. 

Thoughts??

Thanks,
Frank, W1NK