Canon PC940 Service Manual - Page 184

CHAPTER 7 EXTERNALS/AUXILIARY MECHANISMS B. Power Supply Circuit The machine's power supply consists of a composite power supply circuit in which a DC power supply, scanning lamp power supply, and high-voltage power supply are integrated on a single board. It also possesses a microprocessor for exchanges of various data with the machine's DC controller PCB. The machine's power switch is a soft switch, and the machine is equipped with an auxiliary power supply used to operate the switch. The auxiliary power supply provides the microprocessor (Q900) with +5 V as long as the door switch (DS1) remains on. AC power is supplied to the DC power supply when the power switch on the control panel is turned on. In response, the DC power supply provides the DC controller PCB with +5 V, +24 VR, and +24 VU. When the power switch is turned off, the power to the DC controller PCB is cut off. To back it up against 'E000', 'E001', 'E002', and 'E003', the machine is equipped with a DC capacitor as part of the DC controller circuit. When 'E000', 'E001', 'E002', or 'E003' occurs, the capacitor (C123) collects electric charge; if charge exists in the capacitor while the power switch is on, the machine indicates 'E0' on the control panel to indicate that an error related to the fixing heater has occurred. Note: The backup capacitor (C123) retains electric charge for about 5 min after the power switch is turned off. Reference: The tolerances in DC voltage are as follows: • +5 V ±5% • +24 VR ±5% • +24 VU -10.0%, +12.5% For +24 VR, two types of voltage are used: • During copying, +24 V ±5% • During standby, +18 V ±10% However, the above assume that the deviations in AC input are -15%, +10%. 7-4 COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)