Electrical Safety Circuits - Lexmark W820 Service Manual

7.
PSHV-R2
Takes the +24VDC received from the I/O PWB and converts it into the Fuser Bias
voltage.

Electrical Safety Circuits

The printer contains three safety circuits that are controlled by three interlock switches
and one Ground Fault Interrupter (GFI). Cutting power prevents a service technician or a
printer user from being injured by high voltage, by moving parts, or by exposure to the
laser beam.
SW1 (CRU Interlock Switch) is wired in series with SW2. SW1 is closed when the EP
Cartridge is in place inside the printer. When the EP Cartridge is removed from the
printer, SW1 is open. An open SW1 cuts all +24VDC output from the I/O PWB.
SW2 (Left Cover Interlock Switch) is wired in series with SW1. SW2 is closed when the
printer Left Cover is closed. When the Left Cover is open, SW2 is open. An open SW2
cuts all +24VDC output from the I/O PWB.
If either SW1 or SW2 is open, the I/O PWB cuts all +24VDC output.
Front Cover Interlock Switch is connected to the MCU PWB. When the printer Front
Cover is open, the Interlock Switch cuts all +24VDC output from the MCU PWB.
Ground Fault Interrupter (GFI) senses minute amounts of current flowing to ground and
immediately cuts all AC line voltage into the Noise Filter. Faster than conventional circuit
breakers, the main purpose of the GFI is to prevent electrical shocks to the technician or
printer user.
CAUTION: It is dangerous to bypass, or cheat, either the CRU Interlock Switch or the
Left Cover Interlock Switch while the EP Cartridge is out of the printer. With the interlocks
bypassed, the Laser Diode is active and generates intense laser light. Without the EP
Cartridge in place to block the laser beam, you risk serious eye injury.
4025-XXX
1-13
General Information