8.3FUSING TEMPERATURE CONTROL
8.3.1Fusing Circuit Operation
The fusing lamp is powered by the ac drive board and controlled by the main
board.
The ac drive board receives direct wall voltage ac power (not stepped down) at
T201 and T202. It also receives +24 volts at CN202-1. The ac power is applied to
the drive circuit, the fusing lamp, and the triac (TRC201). The dc power drives
PTC201 and RA201.
To turn on the fusing lamp, the main board drops CN106-B14 to LOW. This
activates the photocoupler (PTC201) which in turn energizes the drive circuit.
The drive circuit turns on the triac to complete the lamp circuit, thus turning on
the lamp.
RA201 guards against a failure of the +24 volt power supply. When +24 volts is
applied at CN202-1 and CN106-B15 drops to LOW, RA201 is energized and its
ac contacts stay open. If the +24 volts power from CN 106-A2 stops, the ac
contacts of RA201 close, stopping the drive circuit and turning off the fusing lamp.
Rev. 5/95
A163 2-29 SM
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