Good advice regarding cleaning Tektronix gear (From the "TekScopes" List) - but applicable to any equipment with DC fans... From: "Mac Perkins" (Pacific Studio, Inc) "Spinning up a DC fan with compressed air also makes it a remarkably good generator, whose output voltage can easily exceed its normal supply, damaging either its internal driver circuitry or if you're really lucky other components that share the same power rail. We had a series of mysterious failures on rental units that were routinely blown out on return. The rental warehouse staff liked to see how high a pitch they could create by spinning up the fans with shop air. I did a little testing and found the 12 V rail was around 20 V when this was done, with the rest of the circuitry unpowered, leading to failures of several power drivers. We required that the fan be immobilized before blowing down the units, and the failures stopped. A small screwdriver through the fan works well and is difficult to miss - we tried toothpicks, but they did not always get removed." -- Lyle Bickley, KF6ZGI Bickley Consulting West Inc. http://bickleywest.com "Black holes are where God is dividing by zero"