Motorola MCS 2000 Service Instructions Manual page 133

Troubleshooting Troubleshooting Chart 1-8A, Control Head Model I
PTT input
1. Check that the voltage on U0653 pin 46 changes from 5 VDC to 0 V when P0651 pin 6 is con-
nected to ground (equivalent to pressing PTT on a standard microphone).
2. If this fails, check U0655.
Monitor input
1. Check that the voltage on U0653 pin 45 changes from 5 VDC to 0 V when P0651 pin 3 is con-
nected to ground.
2. If this fails check U0656.
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 U0655.
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 Q0662.
SW B+ in SB9600 mode (high load)
1. Connect a 68 ohm 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 Q0662.
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 U0655/U0656 pin 10 is 0 VDC.
3. If this fails check Q0662 and Q0663.
Volume Control
1. Turn R0698 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 R0698.
Keypad
1. Check that when pressing a key, the correct input to U0653 pins 33-39 goes 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.
Key Backlight
See LCD backlight.
68P81083C20-D
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December 6, 2004