Motorola cm200 Commercial Series, Service Manual

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2-10 THEORY OF OPERATION
Voltage regulator U503 provides 5 V for the RF circuits. Input and output capacitors are used to
reduce the high frequency noise and provide proper operation during battery transients.
5.2 Protection Devices
Diode VR500 acts as protection against ESD, wrong polarity of the supply voltage, and load dump.
VR692 - VR699 are for ESD protection.
5.3 Automatic On/Off
The radio can be switched ON in any one of the following three ways:
• On/Off switch. (No Ignition Mode)
• Ignition and On/Off switch (Ignition Mode)
• Emergency
5.3.1 No Ignition Mode
When the radio is connected to the car battery for the first time, Q500 will be in saturation, Q503 will
cut-off, will pass through R5073, D500, and S5010-pin 6 (On/Off switch). When S5010 is
ON, will pass through S5010-pin5, D511, R5069, R5037 and base of Q505 and move Q505
into saturation. This pulls U501-pin2 through R5038, D502 to 0.2 V and turns On U514 and U501
9.3 V regulator which supplies voltage to all other regulators and consequently turns the radio on,
When U504 (ASFIC_CMP) gets 3.3 V, GCB2 goes to 3.3 V and holds Q505 in saturation, for soft
turn off.
5.3.2 Ignition Mode
When ignition is connected for the first time, it will force high current through Q500 collector, This
will move Q500 out of saturation and consequently Q503 will cut-off. S5010 pin 6 will get ignition
voltage through R601 (for load dump), R610, (R610 & C678 are for ESD protection), VR501,
R5074, and D500. When S5010 is ON, passes through S5010-pin 5, D511, R5069, R5037
and base of Q505 and inserts Q505 into saturation. This pulls U501-pin 2 through R5038, D502 to
0.2 V and turns on U514 and U501 9.3 V regulator which supply voltage to all other regulators and
turns the radio on, When U504 (ASFIC_CMP) get 3.3 V supply, GCB2 goes to 3.3 V and holds
Q505 in saturation state to allow soft turn off.
When ignition is off Q500, Q503 will stay at the same state so S5010 pin 6 will get 0 V from Ignition,
Q504 goes from Sat to Cut, ONOFF_SENSE goes to 3.3 V and it indicates to the radio to soft turn
itself by changing GCB2 to ‘0’ after de registration if necessary.
5.3.3 Emergency Mode
The emergency switch (P1 pin 9), when engaged, grounds the base of Q506 via EMERGENCY
_ACCES_CONN. This switches Q506 to off and consequently resistor R5020 pulls the collector of
Q506 and the base of Q506 to levels above 2 volts. Transistor Q502 switches on and pulls U501
pin2 to ground level, thus turning ON the radio. When the emergency switch is released R5030 pulls
the base of Q506 up to 0.6 volts. This causes the collector of transistor Q506 to go low (0.2 V),
thereby switching Q502 to off.