TM 5-3610-285-14
(b)
Circuit board 700. The voltage divider network of resistors R2, R3, and R4 provide the reference
voltage to pin 3 of voltage comparator U1. The desired developer temperature is selected by adjusting resistor R4 which
establishes the desired reference voltage at pin 3 of U1. If the voltage at pin 2 is greater than the voltage at pin 3, the
output at pin 7 goes high. Transistor Q1 is turned on; therefore, CR1 LED is on. The collector of Q1 goes low, and solid-
state relay U3 is now energized with a high at wire 32 and a low at wire 33. This action energizes the developer heaters.
As the developer temperature increases, the resistance of thermistor RT-1 decreases, and the voltage at pin 2 of voltage
comparator U1 also decreases. When the voltage at pin 2 is less than the voltage at pin 3, the output at pin 7 of voltage
comparator U1goes low. Transistor Q1 is turned off; therefore, CR1 LED is off. The collector of Q1 now goes high, and
solid state relay U3 is deenergized and turns off the developer heaters.
c.
Dryer circuit.
(1)
Controlled by a switch which activates blower. The switch also activates dryer heater element. Dryer
heater element temperature is controlled by dryer thermostat.
(2)
Circuit description.
(a)
Actuating MAIN DRIVE switch (S5) applies an ac voltage on transformer T1. Transformer T1 steps
down the voltage to 16 V ac and circuit CR1 rectifies the voltage to dc.
Rectified dc voltage is filtered by capacitors C1
and C3 and regulated to 12 V dc by voltage regulator U1. Actuating dryer fan switch (S3) delivers 12 V dc to dryer
temperature control circuit board 800 and developer temperature circuit board 700. When the dryer is calling for heat,
transistor Q1 (NPN) on circuit board 800 is turned on with a high at its base.
The collector then goes low. This low is
sensed at voltage inverter U1 pin 6 on standby control circuit board 500. Transistor Q1 (PNP Darlington) on circuit board
500 is turned on with a low at pin 4 of satisfied AND gate U5. This, in turn, energizes solid-state relay U1, thereby
energizing dryer heaters. In addition, transistor Q2 (NPN Darlington) is turned on with a high at pin 8 of standby timer U3
and with a low at the collector of transistor Q1. This energizes solid-state relay U2 and turns dryer blower motor (B1) on.
When the dryer is at operating temperature (AND gate U6, pin 5, on circuit board 500 goes high), and with no film fed
into the detector roller assembly (AND gate U6, pin 6 goes high) within six minutes, the processor will go into standby
mode for eight minutes (standby timer U3, pin 8, low), and then automatically return to run mode to reheat the dryer.
When the dryer reaches temperature, or after ten seconds, if the dryer is not calling for heat, the processor will return to
standby mode (standby timer U3, pin 8, low). In the standby mode, the dryer heaters, blower motor, and drive motor are
off.
d.
Developer and fixer recirculation pumps circuit.
(1)
Provides power to developer and fixer recirculation pumps. The developer and fixer recirculation pumps
circuit is activated by the standby reset switch.
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