OT laser printer question

Re: ********** Intuitively, if the toner smears when touched, I'd assume it wasn't being fused properly, and would investigate the fuser and its control system first. ********** That is correct. If the toner smears when touched, the problem is in the fuser, and it has nothing to do with the HV power supply, drum or anything else. In early laser printer (up to at least the Canon EX engine in the Laserjet 4 and, I think, 5), fusing was done with heated rollers. The upper fusing roller was an aluminum roller with a silicone (non-stick) coating, and inside the hollow roller was a high-power tubular halogen lamp (500 to 900 watts). The lamp was line-operated, thus different for 110v and 220v printers, and the cause of failure was almost always that the lamp had simply burned out (although lamp control problems are possible, but not common -- the lamp does not burn continuously, it's cycled based on the roller temperature). The lamp can be replaced ($30-ish, typically) by a technician who knows what they are doing, but it's more common to replace the entire fuser assembly ($100+ in most cases). Later models (those that have near-zero warm-up) use "thin film fusing", which is more sophisticated, much more power efficient, and also more complex and difficult to repair unless you go for the swap of the entire fusing sub-assembly.