Electronic On/Off; Emergency - Motorola GM1200E Service Manual

Open Controller
Regulator U0601 is used to generate the 9.3 volts required by some audio circuits, the RF circuitry
and power control circuitry. Input and output capacitors (C0601-C0603 and C0604/C0605) are used
to reduce high frequency noise. R0602/R0603 set the output voltage of the regulator. If the voltage
at pin 1 is greater than 1.3 volts the regulator output decreases and if the voltage is less than 1.3
volts the regulator output increases. This regulator output is electronically enabled by a 0 volt signal
on pin 2. Q0601 and associated circuitry (R0601/R0604/R0605) are used to disable the regulator
when the radio is turned off.
UNSW 5V is only used in a few areas which draw low current and require 5 V while the radio is off.
UNSW 5V CL is used to buffer the internal RAM. C0622 allows the battery voltage to be
disconnected for a couple of seconds without losing RAM parameters. Diode D0621 prevents radio
circuitry from discharging this capacitor.
The voltage 9V3 SUPP is only used in the VHF radio (T1) to supply the drain current for the RF MOS
FET in the PA. The voltage SW B+ is monitored by the µ P through the voltage divider R0641/R0642
and line BATTERY VOLTAGE. Diode VR0641 limits the divided voltage to 5.1V to protect the µ P.
Diode D5601 (UHF) / D3601 (VHF) / D2601 (MB) located on the PA section acts as protection
against transients and wrong polarity of the supply voltage.
2.3

Electronic On/Off

The radio has circuitry which allows radio software and/or external triggers to turn the radio on or off
without direct user action. For example, automatic turn on when ignition is sensed and off when
ignition is off.
Q0611 is used to provide SW B+ to the various radio circuits. Q0611 contains a pnp and an npn
transistor and acts as an electronic on/off switch. The switch is on when the collector of the npn
transistor (Q0611-1) is low. When the radio is off the pnp transistor is cutoff and the voltage at pin 1
is at A+. This effectively prevents current flow through the pnp transistor from emitter (pin 3) to
collector (pin 2).
When the radio is turned on the voltage at the Q0611 pin 4 is high (about 4.4V) and the npn
transistor switches on (saturation) and pulls down the voltage at the base of the pnp transistor. With
Transistor Q0611 now "enabled" current flows through the device from pin 3 to pin 2. This path has a
very low impedance (less than 1 ohm) from emitter to collector. This effectively provides the same
voltage level at SWB+ as at A+.
The electronic on/off circuitry can be enabled by the microprocessor (through ASFIC port GCB2,
line B+ CONTROL), the emergency switch (line EMERGENCY CONTROL), the mechanical On/Off
button on the control head (line ON OFF CONTROL), or the ignition sense circuitry (line IGNITION
CONTROL). If any of the 4 paths cause a low at Q0611 pin 1, the electronic ON is engaged.
2.4

Emergency

The emergency switch (J0400-9), when engaged, grounds the base of Q0441 and pulls the line
EMERGENCY CONTROL to low via D0441. EMER IGN SENSE is pulled high by R0441. When the
emergency switch is released the base of Q0441 is pulled high by R0442. This causes the collector
of transistor Q0441 to go low (0.2V), thereby setting the EMER IGN SENSE line to low.
3.1-2 Introduction/Theory of Operation