Service Manual

MM-E 2072-09333-00
2-37
c. Reverse Power Protection. The V_REV_RADIO voltage passes through the peak detector (U14,
CR811) to the reverse power comparator, U13: when the reverse power increases, the output
(pin 5) voltage decreases, resulting in a higher voltage at the emitter of Q23, which drives the
V_ALC line.
d. Overheat Protection. The thermistor RT3 causes the voltage on the V_TEMP_PA line
(monitored by U5008, located on the LORD module), to be proportional to the internal
temperature.
When the temperature is too high, the voltage on the V_TEMP_PA line exceeds the threshold of
the comparator U9, and the TEMP1 lines assumes a high level. This turns Q19 on, and turns off
the bias voltages via the BIAS_EN line.
2-5.6 Power Supply Subsystem
Refer to Figure A-2.F.
a. ON/OFF Switch and Surge Protector. The ON/OFF switch comprising the MOSFETs Q14,
Q26, connects the DC input voltage to the internal power supply line, SW BAT, only if the
GATE output of the surge stopper U23 provides a sufficiently high gate drive voltage. This
occurs only when the Micom-Z is turned on (provided the polarity of the input voltage is
correct: otherwise, U23 shut down input is pulled to ground even if the DC_PWR_EN line is
connected to ground by switching the Micom-Z ON).
Moreover, Q14 and Q26 will be turned off by U23 if the input voltage line, DC_PWR_IN, is
not within the allowed range.
When Q14 and Q26 are both ON, the input voltage is connected to the internal protected supply
voltage line, SW_BATT.
The SW_BATT line is monitored by U5008, located on the LORD module, via the battery
voltage monitor, U10.
b. Micom-Z Power Supply. The SW_BATT line is used to power the dual switching regulator,
U20.
One section of U20 drives the step-down converter that powers the +10V linear regulator, U21.
The linear regulator U16 uses the +10 VDC voltage to provide +8 VDC.
The other section of U20 drives the step-down converter that powers the +5 VDC linear
regulator, U2.
c. ATU DC Power Switch. The SW_BATT line can be connected to the DC_ANT_CPLR line by
the switch Q15.
To turn Q15 on, the LORD module provides a high level on the CH_CHANGE line.
The current flowing through Q15 is monitored by Q802: if the current is too high, Q803
saturates, and resets the latch U22. The resulting low level on the LATCH line turns Q15 off.
The TUNER_CURR_LIM line is also monitored by the LORD module.