HP 8550mfp Service Manual - Page 168
Fuser control, Table 31., Fusing temperatures
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Fuser control The fuser controller directly interfaces with both the power supply and controller board. As the surface temperature of the upper and lower fusing rollers rises, the resistance of the thermistors drops and the voltage of the fusing temperature detection signals also drops. Table 31 shows the temperatures the formatter sets, based on the media in use. Table 31. Fusing temperatures Target temperature Color mode Number of sheets Full color 1st sheet 2nd and after Black and 1st sheet white 2nd and after Plain paper 175° C 347° F 165° C 329° F 180° C 356° F 165° C 329° F Fusing mode OHT Heavy or glossy Envelope 175° C 347° F 170° C 338° F 175° C 347° F 170° C 338° F 175° C 347° F 165° C 329° F 175° C 347° F 165° C 329° F 180° C 356° F 180° C 356° F 180° C 356° F 170° C 338° F Problems in the fuser can be detected in the following three circuits: Controller board. If the fuser is heated abnormally or does not reach the specified temperature for some reason, the controller board interrupts power to the fuser heaters. From there, the formatter assesses the fusing heater failure and signals the printer control panel. Fusing heater safety circuit (in the power supply circuit). If the fusing heater safety circuit detects an upper or lower fusing heater failure, the safety circuit interrupts power to the upper and lower fusing heaters. Fuser abnormality detection circuit (in the power supply circuit). If there are broken wires to the fusing heater system, the fuser abnormality detection circuit detects no AC current flow, causing the controller board to assess the broken wires, stop driving the fusing heaters, and signal the printer control panel. 166 Chapter 5 - Theory of operation EN