Motorola MCS 2000 Service Instructions Manual page 135

Troubleshooting Troubleshooting Chart 1-8A, Control Head Model I
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, R0679, R0678 and C0668.
Multiplexer in keyload position
Check that U0653 pin 42 goes to 5 VDC. If not check U0653.
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 U0655 and U0656.
2. Also check D0683, D0684, D0685 and D0676.
Microprocessor U0653
Replacement of U0653 requires special factory programming and alignment (currently not available
in the radio service software).
68P81083C20-D
9-19
December 6, 2004