Canon NP6218, FY8-13EX-000 service manual C. Controlling the Scanning Lamp, Outline

CHAPTER 4 IMAGE FORMATION SYSTEM

C. Controlling the Scanning Lamp

1. Outline

Figure 4-104 shows the circuit that controls the scanning lamp; the circuit has the following functions:

•turns on and off the scanning lamp.

•controls scanning lamp pre-heating operation.

•controls scanning lamp intensity.

•controls the scanning lamp heater.

The copier’s scanning lamp is a fluorescent lamp.

In general, a fluorescent lamp is low in intensity immediately after power-on, gradually increasing in intensity as time passes, without control; in particular, it takes a long time before the intensity stabilizes in a low temperature environment.

If the ambient temperature drops below 15°C, the copier may enter and remain in wait state before a specific intensity can be obtained. To prevent this from occurring, a fluorescent lamp is provided for installation in low temperature environments.

To ensure that the lamp exposes an original at a stable intensity, a fluorescent lamp adjusting sensor is used to monitor the intensity of the lamp during copying operation, thereby controlling it to a specific value.

In addition, half pre-heating is executed between power-on and a press on the Copy Start key so as to ensure that the lamp reaches its optimum intensity within a short period of time after a press on the Copy Start key; thereafter, full pre-heating is performed. (See Figure 4-105.)

			J205	T401Composite power				DC controller PCB
				supply PCB
				Fluorescent		FLPRHT*	J211-3
(FL1)				lamp pre-	32KHzCLC
				heating circuit
Scanning lamp								Micro-
			T101					processor
								(Q301)
			Main switch	Fluorescent	FL ON
						Micro-
				lamp drive	MPWM
						processor
				circuit
						(Q512)
					FLS
									VR301
SW2			T103
							J302-9		Reversal
			Main transformer
									amplifier
Fluorescent lamp			(T101) drive circuit				J211-9
								5V	circuit
heater switch
	J202-1		Q108	Fluorescent lamp	FLHTOFF*
(H2)				heater	FLTH
			FLTHON
				control circuit
		-2
Fluorescent lamp
heater
(TH3)						FLTH	J317-1
							-2
Fluorescent lamp
thermistor
Fluores	J701-1
cent lamp		-3					-4
intensity
sensor
				Figure 4-104

4-4 COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)