394 CODEC and Audio Fault Finding TM9100 Service Manual© Tait Electronics Limited August 200513.6 Faulty Modulation Using Auxiliary ConnectorIntroduction This section covers the case where the transmitter operates normally butthere is no modulation (although there is modulation at the auxiliaryconnector). There are two tasks:■ Task 15: apply AUD TAP IN signal■ Task 16: check CODEC 2 deviceIf there was also a fault with the speaker audio at the auxiliary connector, itis assumed that this has now been rectified.Task 15 —Apply AUD TAP INSignalFirst check the modulation and, if necessary, the DC offset.1. Enter the CCTM command 33 to place the radio in transmit mode.(The frequency is that of channel 1.)2. Check the modulation via the microphone input.3. Enter the CCTM command 32 to place the radio in receive mode.4. If the modulation is correct, go to Step 5. If it is not, go to Task 12of “Faulty Modulation” on page 390.5. Apply a 1kHz AC-coupled signal of 0.7V pp at pin 7 (AUD TAP IN) ofthe auxiliary connector (alternatively, as ITF AUD TAP IN at the junctionof R237 and R241 — see Figure 13.10).6. Enter the CCTM command 323 t5.7. Check the DC offset voltage at pin 7:8. If the above DC offset is correct, go to Step 9. If it is not, go toStep 11.9. Remove the CDC TOP can.10. Check for and repair any soldering faults around IC205, or elsereplace IC205 (see Figure 13.10). Conclude with Step 12.11. Check for shorts at pin 7 of the auxiliary connector. If there are none,go to Task 16. If there are, repair the fault and conclude with Step 12.12. Confirm the removal of the fault and go to “Final Tasks” onpage 147. If the repair failed, replace the main-board assembly and goto “Final Tasks” on page 147.pin 7 of auxiliary connector: approximately 1.5V DC offset
