Section 4: Troubleshooting
4- 4
Table 4-1: Troubleshooting Guide (Continued)
Symptom Probable Cause Corrective Action
One or more keys
on the front panel
keypad does not
work. (Continued)
CPU PCB has failed. Replace the CPU PCB with a
known good PCB.
One or more
display segments
does not work.
An LCD PCB
component has
failed.
Inspect the LCD PCB
components and circuit board
for cracking, burning, or damage
and replace the LCD PCB if any
are found.
Flex circuit between
LCD and LCD PCB
has come loose.
Inspect the flex circuit between
the LCD and the LCD PCB has
come loose and replace the LCD
PCB if loose.
Replace the LCD PCB with a
known good PCB.
Beeper does not
beep for pulse
indication or no
sound can be heard
from the beeper.
The beeper has been
turned off or its
volume is turned
down too low to hear.
Turn the beeper back on.
The holes for the
beeper on the back of
the NPB-40 are
blocked.
Clear the holes for the beeper on
the back of the NPB-40.
The external output
port on the CPU PCB
has failed.
Replace the CPU PCB with a
known good PCB.
The beeper on the
LCD PCB has failed
Replace the LCD PCB with a
known good PCB.
Pulse rate or SpO2
value is not
displayed and the
unit is on.
The SpO2 sensor is
not connected
properly.
Connect the SpO2 sensor to the
NPB-40.
The SpO2 sensor has
failed.
Replace the SpO2 sensor with a
known good SpO2 sensor.
A component on the
LCD PCB has failed.
Replace the LCD PCB with a
known good PCB.
A component on the
CPU PCB has failed.
Replace the CPU PCB with a
known good PCB.
LCD backlight does
not come on when
the Display Light
key is pressed.
The Display Light
key on the front
panel keypad is
defective.
See “One or more keys on the
front panel keypad does not
work,” above.
The backlight LEDs
on the LCD PCB
have failed.
Replace the LCD PCB with a
known good PCB.
The unit shuts off
when the LCD
backlight is turned
on.
The batteries are at
or near a voltage too
low for the NPB-40 to
operate.
Install new batteries.
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