Fusing Control - Ricoh FT5540 Service Manual

12.7 FUSING CONTROL

The main board monitors the fusing temperature through the fusing thermistor to control the
fusing temperature. It also uses the zero-cross signal generated by the ac drive PCB to
accurately control the applied power.
Normally, the voltage applied to the lamp is a full ac waveform. However, by removing jumper
JP100 on the main board, fusing power is phase controlled. (Note: phase control should only
be used if the customer has a problem with electrical noise or interference.)
Full AC Waveform
When the main switch is turned on, the main board outputs a trigger signal [C] to the ac drive
PCB. This trigger signal has the same frequency as the zero-cross signal [B]. The trigger
signal allows maximum ac power [D] to be applied to the fusing lamp. Then, when the
operating temperature is reached, the CPU removes the trigger (HIGH) and the fusing lamp
turns off.
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31 August 1989