Just a follow-up. There are several other fans in this unit. I had
suspected a thermistor on the lamp as the culprit but as I tested I
found that when this over-temp condition is triggered, a different
failure mode occurs. Also the fans speed up so I suspect the 8v is a
variable voltage/speed fan as James suggested. The other thing I
discovered is that it does make a diffference if you don't have a
changing presentation on the screen as it does turn-off after a while
with no changing input. In the end, I replaced the fan and it seems
to be working correctly now. Thanks to all who commented and made
suggestions.