[time-nuts] Thunderbolt temperature anomaly

[msproul]

I have a Tbolt  (labeled Rev. E, 5/31/05) that seems to be working 
properly, except for the
temperature display in Lady Heather. When I start the program the 
display will come up
typically showing the temperature as a straight line at 39.749981C 
and DAC voltage is -0.073xxx.
The temperature and DAC will remain at these values for hours. Occasionally
the temperature will change to 40.749981 or 38.749981. Rarely, it 
will go to 37.749981.
In all cases, when the temperature shifts it occurs over a few minutes and is
a series of saw-tooth steps. It then remains as a straight line for hours.
Except during the transition, the temperature is always xx.749981.

What could cause this and does it indicate any serious problem?

Other Lady Heather plots I have seen show the temperature plot
being similar to a sine wave following the small temperature changes.

Thanks for any comments/suggestions.

Maury