Motorola MCS 2000 Service Instructions Manual page 139

Troubleshooting Troubleshooting Chart 1-8B, Control Head Models II & III
Multiplexer in Normal Position
1. Check that the voltage on U0657/U0658/U0659 pin 10 is 5 VDC.
2. If this fails check Q0664 and Q0665.
PTT input
1. Check that the voltage on U0653 pin 9 changes from 5 VDC to approx. 1.7 VDC when P0651
pin 6 is connected to ground (equivalent to pressing PTT on a standard microphone).
2. If this fails, check U0657.
Monitor input
1. Check that the voltage on U0653 pin 9 changes from 5 VDC to approx. 3.3 VDC when P0651
pin 3 is connected to ground.
2. If this fails check U0658.
AUX input
1. Check that the voltage on U0653 pin 5 changes from 5 VDC to approx. 0 VDC when P0651
pin 7 is connected to ground.
2. If this fails check U0659.
SW B+ in SB9600 mode
1. Connect a 5.6 kohm resistor from P0651 pin 1 to ground (a keypad microphone can be used
instead).
2. Check that the DC voltage on P0651 pin 1 is still approx. 12 VDC.
3. If not check Q0664.
SW B+ in SB9600 mode (high load)
1. Connect a 68 ohms resistor from P0651 pin 1 to ground.
2. Check that the DC voltage on P0651 pin 1 is still approx. 12 VDC.
3. If not check Q0664.
Multiplexer in SB9600 position
1. Connect a 5.6 kohm resistor from P0651 pin 1 to ground (a keypad microphone can be used
instead).
2. Check that the voltage on U0657/U0658/U0659 pin 10 is 0 VDC.
3. If this fails check Q0664 and Q0665.
Volume Control
1. Turn R0696 fully counter clockwise and then fully clockwise and verify the voltage on U0653
pin 14 goes from 0 V to 5 VDC.
2. If not, check R0696.
Keypad
1. Check that when pressing a key, both a column and a row input to U0653 pins 35-39 (rows)
and 45-49 (columns) go low. The actual pins can be found on the schematic diagram.
2. Clean the carbon pads with alcohol.
3. Check carbon on rubber keypad. If defect, replace keypad.
68P81083C20-D
9-23
December 6, 2004