2. Turning On and Off the Scanning LampThe microprocessor on the DC controller PCB turns on the transistor (Q147) to sendthe lamp ON command (LMPON) to the lamp regulator.When the DC controller generates the light intensity signal (LINT), voltage of about135 to 140 V (220 / 240 V) / 80 to 95 V (120 V) is supplied to the lamp, thereby turningon the scanning lamp.Reference:If the density of copies has become excessively low because of deterioration in thesensitivity of the drum, you may make correction by adjusting the setting of ‘301’ inservice mode or ‘U21’ in user mode. (However, the setting in user mode ‘U21’ isnarrower than that of the service mode the range of the adjustment.)A lower setting will increase the value of the LINT signal (analog) and, as a result,will raise the supply voltage to the lamp, thereby increasing its intensity.3. Detecting the Activation of the Scanning LampThe lamp regulator sends the lamp ON detection signal (LDT) to the DC controllerwhile the scanning lamp is on.If the LDT signal remains on for 22 sec, the DC controller will identify the conditionas an error and, as a result, will generate the power switch OFF signal (PWOFF*) to turnoff the power switch and cut off the AC power supply.4. Protection MechanismThe machine is equipped with a thermal fuse to prevent malfunction of the scanninglamp.The thermal fuse (FU1) will melt in response to overheating (about 104°C / 219F ormore) because of a short circuit or the like around the scanning lamp, thereby cutting thepower supplied to the scanning lamp.4-4CHAPTER 4 IMAGE FORMATION SYSTEMCOPYRIGHT © 1997 CANON INC. CANON NP6330 REV.0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
