TM8100/TM8200 Service Manual Transmitter Fault Finding (25W) 341© Tait Electronics Limited November 200712 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 offault is manifested when the radio always transmits at full power, even if setotherwise. Regardless of the fault, the lock status should be normal.Fault-DiagnosisTasksThe procedure for diagnosing transmitter faults is divided into tasks, whichare 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 thefollowing information regarding CCTM commands, frequency bands, canremoval 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 TestMode (CCTM)” on page 123.Table 12.1 CCTM commands required for the diagnosis of faults in the transmitterCommand Description32 Set radio in receive mode33 Set radio in transmit mode47 Read temperature near PAs — displays temperature x in degrees celsius and voltage y101 x y 0 Set transmit frequency (x in hertz) and receive frequency (y in hertz) to specified values114 x Set DAC value x (in range 0 to 1023) of transmit power304 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 driver318 Read forward-power level — displays corresponding voltage x in millivolts319 Read reverse-power level — displays corresponding voltage x in millivolts326 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 PA332 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 PA334 x Set synthesizer on (x=1) or off (x=0) via DIG SYN EN line335 x Set transmit-receive switch on (x=1) or off (x=0) via DIG SYN TR SW line
