Control Heads Ii And Iii Troubleshooting Procedure - Motorola MCS 2000 Service Instructions Manual

Troubleshooting Troubleshooting Chart 1-8B, Control Head Models II & III

Control Heads II and III Troubleshooting Procedure

Power Supply
Check that the radio is connected to a power supply.
ON/OFF switch
1. Check that radio turns on. I.e. SW B+ is 12V DC. If not, press the ON/OFF switch to turn off
radio.
2. If the radio does not turn on, verify that there is DC voltage on the MIC-HI/ON_OFF line and
that this voltage goes to ground when pressing the ON/OFF switch.
3. If the DC voltage is present but does not go low check J0650 and R0696.
5V DC supply
1. 12VDC is now assumed to be present both on A+ and SW B+.
2. Check that there is 5 VDC on TP3. If not check R0651 and U0650.
Reset
Check that the control head reset is functional.
Radio resets control head
1. Monitor uP reset on U0653 pin 18 with an oscilloscope. Turn radio off and on.
2. Check that the uP reset goes from low to high (5 VDC) after power up and stays high.
Check reset circuit
1. If U0653 is not reset check Q0655 and U0660.
2. Check that D0660 is not shorted.
Check the undervoltage detector IC U0660
1. Disconnect the control head from the radio and connect J0650 pins 7 and 13 to ground and
pins 17 and 18 to a variable DC supply.
2. Measure the DC voltage at TP3.
3. Monitor U0660 pin 1.
4. Increase slowly the DC supply starting from 4 V.
5. Check that U0660 pin 1 changes from 0V to 5 VDC when TP3 is approx. 4.3 V. If not replace
U0660.
6. Connect J0650 pin 3 to TP3. Check that U0660 pin 1 goes low. If not replace Q0665.
Continuous reset
If the control head is continuously reset by the radio it may be due to a bus communication problem
or the microprocessor not working.
Microprocessor Clock
1. Check that the microprocessor oscillator is working (4 MHz square wave on TP2). If not
check Y0650 and U0653.
2. Clean PCB area round Y0650.
68P81083C20-D
9-21
December 6, 2004