HP 8550 Service Manual - Page 196
Controlling the pre-heating mechanism of the, scanning lamp, Turning on and off the scanning lamp
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Controlling the pre-heating mechanism of the scanning lamp To reduce the time required for the scanning lamp to reach its optimum intensity after COPY START is pressed, the filament of the scanning lamp is supplied with power. This mechanism is called "preheating," and it may be standby pre-heating, pre-activation preheating, or activation pre-heating. l Standby pre-heating-The filament is supplied with a voltage of 2.9 ±0.25 V after power-on, during initial rotation, and after copying. If the lamp turns on and then off at the end of copying, standby pre-heating is ended and it will be started as soon as the lamp heater turns on next time. Thereafter, standby pre-heating remains on until the next time the lamp turns on. l Pre-activation pre-heating-The filament is supplied with a voltage of 4.35 ±0.45 V 1.5 seconds before the scanning lamp is turned on for copying. l Activation pre-heating-The filament is supplied with a voltage of 3.8 ±0.4 V during copying. Thereafter, a voltage determined based on the intensity duty value read while the scanning lamp is on will be applied. Turning on and off the scanning lamp The scanning lamp is turned on and off by the scanning lamp on signal (FLPWM), scanning lamp clock signal (FLCLK), and scanning lamp ON signal (FLONOUT) from the reader controller PCB. Controlling the intensity of the scanning lamp The FLPWM signal is a pulse signal, and the intensity of the scanning lamp is controlled so that it remains a constant level by changing the duty ratio of the signal according to the scanning lamp intensity signal (FL_S) detected by the intensity detection PCB and the scanning lamp VR setting. 194 Chapter 5 - Theory of operation EN