Fusing Lamp Control Circuit; Fusing Lamp - Ricoh M5 Service Manual

4. Fusing Lamp Control Circuit

Above is a schematic of the fusing lamp control circuit.
which are coupled through a photocoupler.
The following discussion centers on circuit operation from the viewpoint of the signals that can be
observed between the main board and the ac drive board.
– Fusing Lamp ON/OFF –
To turn on the fusing lamp, the CPU supplies LOW (ground) at CN103-13.
This supplies ac power to the fusing lamp.
vious section.
The CPU decides whether to apply a continuous LOW or a continuous HIGH (lamp
OFF) based on the input from the TH at CN101-1.
resistance decreases) as the hot roller's temperature rises.
— Software Overhe at Protection —
IC-102, IC-105, and Q-101 form an overheat protection circuit.
within the normal range, pin 1 of IC-102 stays LOW, therefore, Q-101 stays on, allowing PC-501 to
operate.
If the hot roller temperature reaches 195 degrees Celsius, the resistance of TH becomes approx-
imately 1 kilo-ohm.
PC-501 operation.
At that point, pin 1 of IC-102 becomes HIGH, turning off Q-101 and preventing
The circuit has both ac and de components,
This LOW signal is the enable signal discussed in the pre-
The voltage received at CN101-1 increases (TH
3 - 6 8
May,
When the fusing unit is operating
25, 1985