Motorola ASTRO MT 1500, Service Manual

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Chapter 3.2 UHF1 Radio Power
3.2.1 Introduction
This chapter of the manual provides a detailed circuit description of the power distribution for an
ASTRO XTS 2500/XTS 2500
I
digital portable radio. This manual is to be used in conjunction with the
ASTRO XTS 2500/XTS 2500
I
Digital Portable Radios Basic Service Manual (Motorola part number
6816984H01), which uses the pass/fail service approach to radio problems.
3.2.2 Radio Power Up or Down
Radio power up begins when the radio ON/OFF/Volume control knob is turned to the on position,
placing 7.5 volts on the MECH_SW line. This signal activates the pass element (Q700, Q701 and
Q703), enabling SW_B+ and .
The 7.5 Volts on the MECH_SW line turns Q701 ON, which in turn drives the MECH_SW pin on the
MAKO IC (U701) low. With the high-low transition on the MECH_SW pin, the MAKO IC then pulls the
FET_ENX pin (or VPP_EN line) low, enabling external P-MOSFETs Q700 and Q703. Q700 and
Q703 applies SW_B+ to MAKO IC and VoCon and to the RF section of the board. After
application of the power to SW_B+, the regulators VSW1, VSW2, V1.875, V1.55, V2.9 and VCC5
are sequentially turned ON. After the regulators are stable, the RESETX pin is asserted low for an
additional 16ms and then released to allow the dual-core processor to start.
The radio power down sequence begins from the ON/OFF switch that disables Q701. This causes
the MECH_SW pin on the MAKO IC to be pulled High. Then, the INT_X pin (or MAKO_INT) is drawn
low and the 125ms Watchdog timer is started. The dual core processor (through SPI communication
busses) then initiates the powering down process of the radio. At this point, the watchdog timer can
be kept alive by the dual-core processor (via the SPI bus) allowing for software cleanup. Upon
expiration of the watchdog timer, the MAKO IC asserts the RESETX pin and turns off all DC
regulators including SW_B+ and (Q700 and Q703 turn off when the MAKO IC drives the
FET_ENX pin high).
3.2.3 General
In the XTS 2500/XTS 2500
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radio, power (B+) is distributed to one board that contains both the
transceiver and controller sections. There is an additional backup battery (Motorola part number
6003710K08) mounted directly on the board; see the basic service manual for details.
Power for the radio is provided through a battery supplying a nominal 7.5Vdc directly to the
transceiver. The battery is available in the following forms:
• NTN9815_ Nickel-Cadmium, Hi Capacity
• NTN9816_ Nickel-Cadmium, Hi Capacity, FM Approved
• NNTN9857_ Jedray NiMH Impres Standard Battery
• NNTN9858_ Jedray NiMH Impres FM Battery
• NNTN6263_ Jedray NiMH Impres FM Immersible Battery
B+ from the battery is electrically switched to most of the radio, rather than routed through the ON/
OFF/Volume control knob, S501. The electrical switching of B+ supports a “keep-alive” mode. Under
software control, even though the ON/OFF/Volume control knob has been turned to the “off” position,
power remains on until the MCU completes its power-down sequence.