Brother LX-200 Service Manual page 158

2
Nothing happens when switches are pressed.
a. Defective switch or leaf switch on the Switch PCB.
b. Defective LED on the Switch PCB.
Problem Check Item
a. Defective Is Switch PCB correctly
switch or leaf mounted?
switch on the
Switch PCB
Is switch harness assy
correctly connected?
Is the red lead connector
connected to CN2 on the
Switch PCB?
Is the white lead connector
connected to CN3 on the
Switch PCB?
Is the yellow lead connector
connected to CN4 on the
Switch PCB?
When switch SW1 to SW4 is
pressed on the Switch PCB,
does the switch become
conducting?
When the cover R/cover L
leaf switch is shorted, does
the connector on the leaf
switch assy become
conducting?
When switch SW1 to SW4 is
pressed on the Switch PCB
or the leaf switch assy is
shorted, can the conductivity
be checked at CN1 on the
main CPU?
If conductivity can be
checked at CN1 on the main
CPU when switch SW1 to
SW4 is pressed or the leaf
switch assy is shorted, can
the conductivity be checked
at the main CPU ports?
If conductivity can be
checked at the main CPU
ports when switch SW1 to
SW4 is pressed or the leaf
switch assy is shorted, is this
recognized by the main
CPU?
Cause
Defective Switch PCB Correctly mount
mounting. Switch PCB.
Defective connection of Correctly connect
switch harness assy. switch harness assy.
Leaf switch assy not Correctly connect the
connected. leaf switch assy.
Leaf switch assy not Correctly connect the
connected. leaf switch assy.
Leaf switch assy not Correctly connect the
connected. leaf switch assy.
Continuity problem in Replace the Switch
switch SW1 to SW4. PCB.
Defective leaf switch Replace cover switch
assy. assy.
Replace leaf switch
R assy.
Replace leaf switch L
assy.
Defective switch Replace switch
harness assy. harness assy.
Continuity problem in Replace Main PCB
Main PCB. assy.
Defective series Replace Main PCB
resistor on main CPU. assy.
Defective main CPU#1. Replace Main PCB
assy.
7-6
Remedy Repair
Replace
switch SW1
to SW4.
Replace
series
resistor.
Replace
CPU#1.
See
Section
3.3.3
3.3.4
3.3.5
3.3.7
3.3.8
3.3.9
3.3.3
3.3.4
3.3.5
3.5.1