7-1. Main control circuits ................................... 7-1 7-1-1. Toner density control .............................. 7-1 7-1-2. Fusing temperature control .................... 7-2 7-1-3. JAM detection .......................................... 7-3 7-1-4. Safety circuit ............................................ 7-4
7-2. Timing chart ................................................ 7-5 7-2-1. A4, TWO COPIES, CASSETTE PAPER FEED (UPPER) .......................................... 7-5 7-2-2. A4, TWO COPIES, CASSETTE PAPER FEED (LOWER) ......................................... 7-5
7-3. Connector list .............................................. 7-6 7-3-1. Main CB (UNIT MAIN) .............................. 7-6 7-3-2. High voltage unit (UNIT HV) .................... 7-9 7-3-3. Power supply board (UNIT PSU) .......... 7-12
7-4. IC list .......................................................... 7-13
7-5. Test points and VR list ............................. 7-14
7-1. Main control circuits 7-1-1. Toner density control 1. Toner density detection The TNS signal detected by the toner sensor is relayed by the high voltage unit (UNIT HV) and connected to CN191-20 on the main CB (UNIT MAIN). After the TNS signal is changed to a partial voltage (TNS! signal) by the registance in the main CB, it is input into the IC121 (CPU) pin No. 77. The TNS! signal can be measured with the test point (TP103). 1 2. Toner motor drive control As the toner is consumed and the toner density becomes lighter than the optimum density, the TSM signal is output (HIGH -> LOW) from the IC121 No. 23 pin. The drive circuit in the high voltage PCB (UNIT HV) is acti- vated to rotate the toner motor (pulse motor) and supply the toner. Supply time: 3.5 sec. 1 3. Forced toner supply mode If the toner sensor detects a light density 1% less than the optimum density three times in succession, this unit will stop the copy operation, and forcibly supply toner. During this mode's operation, P25 will display (forcibly supplying toner).time: Max. 250 sec. When the toner density is recovered (6.5%), the stopped copy job will automatically resume. However, if the density is not recovered, P25 will blink (toner empty), and after 30 copies, the copy operation will stop. 4. Initialization of developing unit When the unit's power is turned on in the unused state (when installed), P26 will light (developer not initialized), and the standby state will not be entered. This is so that the compensation voltage TNSC signal (analog voltage) applied on the toner sensor can be calculated beforehand so that the TNS signal will become the reference voltage in the new developer (unused) state. When the initialization operation (user mode C-51) is carried out, the detected compensation data will be saved in the main PCB's EEPROM (IC123). (Note: The developing unit must be initialized also when it has been replaced.) Initialization time: 6 min. (3 min. agitation + 3 min. reading & compensation data registration) +5V UNIT HV +24V
CN1261-4 UNIT MAIN CN191-19 TP103 TNSC TNS! TSMCLK 77 CN191-18 TP104 IC121 CN191-17 /TSM TNSC! 5
TSMCLK 45
TSM 23
MODEL MANUAL REVISED EDITION DATA PAGE METHOD 7-1 1312 SERVICE HANDBOOK 1 May.1999 7-1 REPLACEMENT Chapter 7 Electricity
7-1-2 Fusing temperature control The surface temperature of the heat roller is detected with a thermistor, and is kept to a constant optimum tem- perature (188
