Motorola MCS 2000 Service Instructions Manual page 126

4.1 SB9600 BUS+, J650 pin 15
- This signal is normally 5 VDC with short pulses to 0V when data are sent on the bus. If it is constantly 0
V or 5 VDC check D0665 (most common error), Q0663 and Q0662. Check that U0653 pin 52 is 5 VDC
with pulses to ground while sending data.
- Then check U0659 (disconnect pins 1 and 12). If problem disappears and OPTION SW B+ circuit is OK
(see 5.), replace U0659.
- If the OPTION SW B+ circuit is defect, D0669 should also be checked.
4.2 SB9600 BUS-, J650 pin 4
- This signal is normally 0 V with short pulses to 5 VDC when data are sent on the bus. If it is constantly 5
VDC or 0 V, check D0664 (most common error), Q0661 and Q0662. Check that U0653 pin 52 is 5 VDC
with pulses to ground while sending data.
- Then check U0657 (disconnect pins 1 and 12). If problem disappears and OPTION BW B+ circuit is OK
(see 5.), replace U0657.
- If the OPTION SW B+ circuit is defect, D0667 should also be checked.
4.3 SB9600 BUSY, J650 pin 14
- This signal is normally 0 V with pulses to 5 VDC when data are sent on the bus. If it is constantly 5 VDC,
check D0659 (most common error) and Q0653. Check that U0653 pin 43 is 5 VDC with pulses to ground
while sending data.
- Then check U0658 (disconnect pins 1 and 12). If problem disappears and OPTION BW B+ circuit is OK
(see 5.), replace U0658.
- If the OPTION SW B+ circuit is defect, D0668 should also be checked.
4.4 SB9600 data in comparator
- If the above voltages are correct, check U0656, Q0660 and Q0662.
- Finally check U0653.
4.5 Communication stops only with accessory on MIC Conn
- If bus communication stops only when an accessory is connected to the MIC Connector (P0651), check
the OPTION SW B+ circuit (See 5.). The accessory is either defect or incompatible.
5 OPTION SW B+/Multiplexing of MIC Connector
Normal mode = No or simple microphone connected.
SB9600 mode = Smart accessory with serial bus connected.
5.1 SW B+ in Normal mode
- Make sure no accessory is connected to the MIC Connector (P0651).
- With power connected to the control head on J0650 pin 17 and 18, check that the DC voltage on P0651
pin 1 is approx. 12 VDC. If not check Q0664.
5.2 Multiplexer in normal position
- Check that the voltage on U0657/U0658/U0659 pin 10 is 5 VDC.
- If this fails check Q0664 and Q0665.
5.3 PTT input
- 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).
- If this fails, check U0657.
9-20 Troubleshooting