Motorola MCS 2000 Service Instructions Manual page 134

9-18
Led Indicators
1. Check that the outputs from U0653 pin 49 (yellow), pin 48 (red) and pin 47 (green) changes
to 5 VDC when LED must go ON.
2. Check Q0659 (yellow), Q0660 (red) and Q0661 (green).
3. Check the LEDs.
LCD backlight
All LEDs
If backlight cannot be turned on or off.
1. Check that U0653 pins 26 and 27 are 5 VDC. If not check U0653.
2. Check that the voltage of base on Q0651 is approx 1.5 VDC.
3. Check Q0651 and U0652.
One/some LEDs
1. One LED is off. Check the LED.
2. One row of LEDs is off. Find the LED that makes the short circuit.
LCD
Defect outside segments of display
If the LCD has either light or dark areas outside the segment, the LCD glass is defect and must be
replaced.
Missing segments
1. Missing segments. Most likely a bad connection between PCB and LCD. Disassemble and
clean PCB and zebra connector with alcohol. LCD glass surfaces can be cleaned with dis-
tilled water with 3% ammonium chloride; never use alcohol on the LCD glass.
2. If necessary replace the zebra connector or LCD.
Weak segments
1. Segment brightness depends on the text displayed. Most likely a short between the lines from
display controller/driver to LCD. Disassemble and clean PCB and zebra connector with alco-
hol. If necessary replace the zebra connector.
2. Check U0651.
NOTE: When monitoring the signal on the LCD controller/driver outputs, a complex signal pattern is
seen that jumps in 4 discrete voltage from 0V to + 5V. Waveform depends on the contents of
the display. Outputs are never steady. A signal can always be seen on a scope unless there
is a short, or the LCD driver is defect.
LCD bias voltage
If segments that should be on are weak or segments that should be off are partly lit, the problem may
be the bias voltage.
1. Measure the LCD bias voltage (DC) between TP1 (+) and GND.
2. The voltage should be approx. 5 VDC or 5.6 VDC depending on the viewing angle setting.
3. Check Q0650.
December 6, 2004
Troubleshooting Troubleshooting Chart 1-8A, Control Head Model I
68P81083C20-D