Tait TM8235, Руководство по обслуживанию

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TM8100/TM8200 Service Manual Transmitter Fault Finding (25W) 323
© Tait Electronics Limited June 2006
12 Transmitter Fault Finding (25W)
Introduction
This section covers the diagnosis of faults in the 25W transmitter circuitry.
The main indication of a fault in the transmitter is a reduction in range.
This implies that the power output is wrong or too low. Another type of
fault is manifested when the radio always transmits at full power, even if set
otherwise. Regardless of the fault, the lock status should be normal.
Fault-Diagnosis
Tasks
The procedure for diagnosing transmitter faults is divided into tasks, which
are grouped into the following sections:
■
“Power Supplies”
■
“Transmitter RF Power”
■
“Biasing of PA Driver and PAs”
■
“RF Signal Path” .
Before beginning the fault diagnosis with “Power Supplies” , note the
following information regarding CCTM commands, frequency bands, can
removal and replacement, and transmit tests.
CCTM Commands
The CCTM commands required in this section are listed in Table 12.1 .
Full details of the commands are given in “Computer-Controlled Test
Mode (CCTM)” on page 118 .
Table 12.1 CCTM commands required for the diagnosis of faults in the transmitter
Command Description
32 Set radio in receive mode
33 Set radio in transmit mode
47 Read temperature near PAs — displays temperature x in degrees celsius and voltage y
101 x y 0 Set transmit frequency ( x in hertz) and receive frequency ( y in hertz) to specified values
114 x Set DAC value x (in range 0 to 1023) of transmit power
304 Read clamp current at gate of PA driver — displays DAC value x (in range 0 to 255)
304 x Set DAC value x (in range 0 to 255) of clamp current at gate of PA driver
318 Read forward-power level — displays corresponding voltage x in millivolts
319 Read reverse-power level — displays corresponding voltage x in millivolts
326 x Set transmitter power level x (0=off, 1=very low, 2=low, 3=medium, 4=high, 5=maximum)
331 Read bias voltage for first PA — displays DAC value x (in range 0 to 255)
331 x Set DAC value x (in range 0 to 255) of bias voltage for first PA
332 Read bias voltage for second PA — displays DAC value x (in range 0 to 255)
332 x Set DAC value x (in range 0 to 255) of bias voltage for second PA
334 x Set synthesizer on ( x =1) or off ( x =0) via DIG SYN EN line
335 x Set transmit-receive switch on ( x =1) or off ( x =0) via DIG SYN TR SW line