(c) The power sharing timer is U5. The zero crossing pulses clocks
this from the power board.
1 Normally gates U4-A and U3-D decide at which count of the
timer priority is shifted from the developer to the dryer.
2 The output of U3-D is initially held low by the action of the flip-
flop U11-B and C, which was determined to be "1" at turn on.
3 The developer heater will run at 100% power until it reaches the
proportional control region.
(d) Once U8B (pin 7) goes high, indicating that the developer is near
operating temperature, a series of events takes place:
1 U4B-5 goes high. This allows the power sharing pulse, which is
generated on a one second interval, to clock through U4-B, setting U4-4 low.
2 U10-10 will then clock low. Meanwhile, the dryer is beginning to
heat up. As soon as it reaches its proportional region, U7B-7 (TP-6) will go high. This
will cause the output of U4D-11 to go from "1" to "0." This will, in turn, reset counter U2.
3 In order for the Temperature Ready light (and therefore the Film
Feed light) to properly function, both the developer and dryer comparator outputs must
either be "1" or make periodic transitions before U2 reaches the end of count. Every
time the comparator output goes high, the Time-Out counter is reset.
(e) Power sharing is effected via the effect of CR-2 on the developer
1 When the output of U10 goes high, voltage is supplied to the
positive input of op amp U8B-5. This turns off the developer heat.
2 When the developer heat is off, U8B-7 is high.
3 This, in turn, supplies power to the output driver, U9B via its
open collector pull up resistor R36.
4 In normal operation, the developer calls for little heat. The dryer
needs more heat and is allowed to run whenever the developer is not calling for heat.