Motorola MCS 2000 Service Instructions Manual page 123

10.2 One/some LEDs
- One LED is off. Check the LED.
- One row of LEDs is off. Find the LED that makes the short circuit.
11 LCD
11.1 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.
11.2 Missing segments
- 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 distilled water with 3%
ammonium chloride; never use alcohol on the LCD glass.
- If necessary replace the zebra connector or LCD.
11.3 Weak segments
- 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 alcohol. If necessary
replace the zebra connector.
- 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.
12 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.
- Measure the LCD bias voltage (DC) between TP1 (+) and GND.
- The voltage should be approx. 5 VDC or 5.6 VDC depending on the viewing angle setting.
- Check Q0650.
13 Secure keyloading
13.1 Secure keyloader sensing
- Connect P0651 pin 2 to ground. Check that DC voltage on U0653 pin 4 goes to 0 V. If not, check P0651,
R0679, R0678 and C0668.
13.2 Multiplexer in keyload position
- Check that U0653 pin 42 goes to 5 VDC. If not check U0653.
13.3 Connections through multiplexer
- Check that P0651 pins 6, 3 and 7 are connected to J0650 pins 10, 12 and 11 respectively. If not check
U0655 and U0656.
- Also check D0683, D0684, D0685 and D0676.
14 Microprocessor U0653
Replacement of U0653 requires special factory programming and alignment (currently not available in
the radio service software).
Troubleshooting 9-17