Lexmark W820 Service Manual page 30

3.
4.
5.
CAUTION: Even though the interlock switches cut the +24VDC output from the MCU
PWB and I/O PWB, +24VDC output from the LVPS is still present throughout the printer
as well as 110VAC line voltage along the AC paths in the printer.
6.
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Service Manual
Low Voltage Power Supply (LVPS)
Takes filtered AC voltage and converts it into regulated +24VDC and +5VDC.
The LVPS contains overcurrent protection circuits. If an excessive current begins
to flow through any of the components supplied by the LVPS, the LVPS immediately
shuts down all low voltage output. To reset the LVPS after an overcurrent shutdown;
switch off the printer, wait a few minutes, then switch on the printer.
The LVPS contains open circuit protection circuits. If the LVPS detects that a
circuit is open for longer than one minute, the LVPS slowly decreases the LVPS
output until the output is zero. To reset the LVPS after an open circuit shutdown;
switch off the printer, wait a few minutes, then switch on the printer.
The LVPS contains a low +24VDC output protection circuit. If the LVPS detects the
+24VDC output dropping below +15VDC, the LVPS slowly decreases the +24VDC
LVPS output until the output is zero.
LVPS Fan: A +24VDC fan that cools the LVPS PWB.
Machine Control Unit (MCU PWB)
Takes the +24VDC and +5VDC generated by the LVPS and distributes them to the
various components through out the printer, including the Printhead.
Front Cover Interlock Switch: Used as a safety measure. If the Interlock Switch is
closed (the Front Cover is closed) the MCU PWB sends +5VDC and +24VDC to
printer components. If the Interlock Switch is open (the Front Cover is open) the
MCU PWB cuts all +24VDC output.
I/O PWB
Takes the +24VDC and +5VDC generated by the LVPS and distributes them to the
various components through out the printer, including the HVPS.
Interlock Switches SW1 and SW2: Used as a safety measure. The main interlock
circuit for the printer is actually two separated switches wired in series with the I/O
PWB. When the EP Cartridge is in place, Interlock Switch SW1 is closed. When the
Left Front Cover is closed, Interlock Switch SW2 is closed. With both switches
closed, the circuit is complete and the I/O PWB sends +24VDC to the HVPS and
other printer components. If either SW1 is open (the EP Cartridge removed) or SW2
is open (the Left Front Cover is open) the I/O PWB cuts all +24VDC output.
High Voltage Power Supply (HVPS)
Takes the +24VDC received from the I/O PWB and converts it into the high voltages
that are required by the printer xerographic components.
The HVPS contains overcurrent protection circuits. If an excessive current begins to
flow through any of the xerographic components, the HVPS immediately shuts down
all high voltage output. To reset the HVPS after an overcurrent shutdown; switch off
the printer, wait a few minutes, then switch on the printer.
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