Motorola MCS 2000 Service Instructions Manual page 141

Troubleshooting Troubleshooting Chart 1-8B, Control Head Models II & III
3. Check U0652 (Model III only).
NOTE: When monitoring the signal on the LCD controller/driver outputs, a complex signal pattern is
seen that jumps in 6 discrete voltages from -3V 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 controller or 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 TP3 (+) and TP1 (-).
2. The voltage should be approx. 8 VDC at ambient temperature.
3. Check that U0654 pin 15 is high. If not check U0654.
4. Check that U0655 pin 8 is approx. -5 VDC. If not check U0655.
5. Check that U0653 pin 3 is approx. 2.5 VDC at ambient temperature. If not check R0742.
6. Check that U0653 pin 20 is a square wave with a DC mean of approx. 3 VDC.
7. If the bias regulation seems to run but the bias is too high or low this may be due to one of the
following:
- Microprocessor has lost its factory adjustment parameters.
- Microprocessor is defect.
8. Reprogramming of microprocessor or replacement of microprocessor requires a new factory
adjustment currently not available in the RSS.
Secure keyloading
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, R0690, R0691 and C0667.
Multiplexer in Keyload Position
Check that U0654 pin 5 goes to 5 VDC. If not check U0654.
Connections through multiplexer
1. Check that P0651 pins 6, 3 and 7 are connected to J0650 pins 10, 12 and 11 respectively. If
not check U0657, U0658 and U0659.
2. Also check D0666, D0661, D0667, D0668, D0669, D0721 and D0722.
Rotary Switch (Model II only)
1. Turn rotary while monitoring normal radio operation.
2. If rotary misses steps or jumps more than one step, replace R0697.
Microprocessor U0653
Replacement of U0653 requires a special factory programming and alignment (currently not
available in the RSS (Radio Service Software)/CPS (Customer Program Software).
68P81083C20-D
9-25
December 6, 2004