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Chapter 7 Electricity




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

7-6. Electrical parts layout drawing ................ 7-14
7-6-1. PCB, lamp (heater), fuse (rating) .......... 7-14
7-6-2. Clutches (solenoid) and motors ........... 7-15
7-6-3. Sensors and switches ........................... 7-15
Chapter 7 Electricity



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




/TSM
CN1251
Q1251 TNM0 1
CI1251B
CI1251C

Q1255 Q1252
Toner supply
motor

Q1253

CN1261-5 TSMCLK TNM1 2
CI1251D +24V
3
CI1251A
4
Q1256 Q1254 Toner sensor
GND24 5
TNS 6

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