Power On/Off; Power On/Off Key; Ignition Signal; Emergency - Hytera MD78X Service Manual

Baseband Section
 Supply for Baseband: The processor U302 is supplied by 3.3V (U900), 1.8V (U903) and 1.6V (U919);
the memory is supplied by 3.3V (U900) and 1.8V (U903) respectively; the audio processor IC is
supplied by 3.3V (U900&U909) and 1.8V (U903); the DAC is supplied by 5V (U905) and 3.3V (U900).
 EXT_SWB+: Q909.
4.2

Power On/Off

The mobile radio can be powered on/off through any of the following methods:
 Power On/Off Key
 Ignition Signal
 Emergency
4.2.1

Power On/Off Key

Power on the radio: As the Power On/Off Key is pressed, R944 becomes grounded and Q910 is on.
Then Q905 outputs high-level signal, causing U902 and Q920 to start working. Afterwards, the
processor U302 executes user routines to maintain a high-level power control signal (PWR_CTR). In
this case, the radio starts to work properly after the Power On/Off Key is released. Power off the radio:
After the Power On/Off Key is pressed, LQ910 is on and a low-level signal (PWB) to power off the
radio is detected by U302, which then controls PWR_CTRL to output low level. Afterwards, the radio
becomes powered off.
4.2.2

Ignition Signal

When the voltage of ignition signal exceeds 7V, Q1 will be turned on by C933, R955 and R956. As a
result, the PNP transistor of Q905 will be further turned on to supply power. Meanwhile, Q401 will also
be turned on, and U302 will identify ignition signals by detecting the signal from Q401; afterwards, the
level PWR_CTRL is generated by the processor.
4.2.3

Emergency

When the emergency alarm pin is at low level, R940 is grounded, and Q906 is turned on to supply
power. Meanwhile, Q908 is also turned on. When low level is detected from Q908 but the radio is
powered off, U302 will output the level PWR_CTRL and send emergency signal. If the radio is
powered on then, U302 will only output emergency signal.
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Service Manual