HM135
Service Manual
Preliminary version
Page 4 of 13
2 CIRCUIT
DESCRIPTION
2.1 General
information
The HM135 is basically divided into 2 printed circuit boards:
Main board
and
Head
. Circuitry and signals can be
divided in the following sections:
Microprocessor/control
Front panel (head) circuitry
VCO / Synthesizer (PLL)
Transmitter
Receiver
Errore. L'origine riferimento non è stata trovata.
ON/OFF switch, rear connector and internal connectors
Refer to the Block Diagram and the Schematics.
2.2 Microprocessor/control
The microprocessor
DD5
is constantly operating when the radio is turned ON. It is continuously monitoring the
keyboard, the PTT line and other internal inputs such as the squelch detect, etc. When a change occurs, the
microprocessor makes the appropriate response according to its program in order to control the all radio
functions. On channel change, the Radio emits a beep and the synthesizer is loaded with the correct frequency
information. The microprocessor runs off a 8 MHz oscillator which is composed of
X3
,
C353
,
C354
and
R319
.
When the radio is first turned on, the microprocessor reads the radio status from the EEPROM
DD3
which
contains all the radio’s parameters.
The microprocessor determinates the receive frequency codes, then loads the synthesizer via its pins
42
(line
PLL_LE
),
43
(line
PLL_DATA
) and
46
(line
PPL_CLK
).
Pin
40
outputs a PWM signal which is converted by
DA18:B
into a CC voltage at its output (line
RF_PWR_CTRL
)
which controls the RF output power.
Pins
37
and pin
39
outputs a PWM signal which are used, respectively, to generate the Selcall signal (line
MCU_SELCALL_PWM
) and CTCSS/DCS signal (line
MCU_CTCSS_DCS_PWM
) as further explained. The
digital signals coming from the ADC converters which drive the microprocessor in order to decode the Selcall and
CXTCSS/DCS signals are applied, respectively, to pin
59
(line
ADC_HI_SPEED_DATA_RX
) and pin
60
(
ADC_lo_SPEED_DATA_RX
).
The firmware program interface is made by means of the connector
XP3
The microprocessor is fitted with an internal program flash memory as well, therefore functions can be
customized, if necessary, upon specific request from the customer.
2.2.a PTT
circuit
The PTT switching is totally controlled by the two microprocessors (
DD5
in the main board and
DD800
in the front
board in the front panel): when the PTT is pressed, the line
AUX_PTT
goes low, so the transistor
VT806
changes
the status of the pin
20
of microprocessor
DD800
which is “informed” that the radio is in TX mode (i.e. PTT is
pressed), so it changes its output at pin
22
putting the low level at pin
8
of the connector
XT802
which is
connected to the main PCB with the connector
XT2
. This means that pin
8
of
XT2
(line
HANDSET_PTT_TO_MPU
) goes low. This line is connected to the
VT56
which changes the status of pin
26
of
the microprocessor
DD5
from hi to low. Now the microprocessor
DD5
is also “informed” that the radio is in TX
mode, so it can control the +8V voltage which is alternatively fed to the TX or RX stages according to the radio’s
status. Pins
29
(line
TX_FROM_MCU
) and
30
(line
RX_FROM_MCU
) control the +8V power switches which
alternatively outputs this voltage to the RX section (line
+8V_RX
) with
VT42
or to the TX one (line
+8V_TX
) with
VT41
.
The transistor
VT805
is controlled by the pin
19
of the microprocessor
DD800
and it is used to eventually disable
all the over stated PTT chain according to the radio’s status (e.g. busy lock out, timeout timer etc).
Содержание HM135
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