Hytera MD78X, Service Manual

Page: 338 / 519

UHF5 (806MHz
–
941MHz)
Circuit Description
15

Supply for Baseband: The processor U302 is supplied by 3.3 V (U900), 1.8 V (U903) and 1.6 V
(U919); the memory (U232/U233) is supplied by 3.3 V (U900) and 1.8 V (U903) respectively; the
audio processor IC (U231) is supplied by 3.3 V (U905&U909&U900) and 1.8 V (U903); the DAC
(U500) is supplied by 5 V (U905) and 3.3 V (U900).

: It is supplied by 13.6 V (Q909).
5.2.2
Control Module
Power On/Off
The mobile radio can be powered on/off through any of the following methods:

Power On/Off Key
The mobile radio is turned on via the
Power On/Off
key. As this 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.
The mobile radio is turned off via the
Power On/Off
key. After this 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.

Ignition Sense
The mobile radio can be turned on when ignition is sensed. When the voltage of ignition signal
exceeds 7 V, Q1 will be turned on by charging of C933, R955 and R956. As a result, the PNP
transistor of Q905 will be further turned on to power the mobile radio. 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.

Emergency
When the emergency alarm pin is at low level, R940 is grounded, and Q906 is turned on to supply
power for the mobile radio. Meanwhile, Q908 is also turned on and the low level is detected from
U302. At this time, if the mobile radio is off, the PWR_CTRL signal will be output to power on the
mobile radio and the emergency signal will be output. However, if the mobile radio is already on, the
emergency alarm pin will be at lower level and only the emergency signal will be output.
Power-on process:
Step 1
Power on the mobile radio using one of the three methods (Power On/Off key, Ignition Sense, or
Emergency);