This is a long shot, but I am trying to help my attending out with a glitch in his slit lamp. Basically, after about 30 seconds the light goes out. After turning it off, the amount of time I wait to turn it back on is proportional to how much time you have to use it before the light goes out again. We think it could be a rheostat issue because with the rheostat on low the bulb is barely lit, then goes out over time. The bulb and power box have been replaced. Anyone have a similar issue or thoughts?