Ricoh FT4460, Service Manual, Page: 126 / 413

28 February 1989
10.3 FUSING CONTROL
The I/O control PCB monitors the fusing temperature through a thermistor
(TH1). It also uses the zero-cross signal generated by the ac drive PCB to ac-
curately control the applied power.
Normally, the voltage applied to the lamp is a full ac waveform. However,
through SP Mode #29, fusing power can be phase controlled. (Normally,
phase control is used only if the customer has a problem with electrical noise
or interference.)
When the main switch is turned on, the I/O control PCB outputs a trigger sig-
nal [C], which has the same timing as the zero-cross signal [B], to the ac
drive PCB. This trigger signal allows maximum ac power to be applied to the
fusing lamp. Then, when the operation temperature is reached, the CPU
removes the trigger (HIGH) and the fusing lamp turns off.
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