Model: Lexus IS sedan
Driving Mileage: 74565 miles
Issue: The customer came to the store and reported that the vehicle's audio (as shown in Figure 1) would not work, and asked for inspection and maintenance.
Troubleshooting: We turned on the radio after starting the car and found that there was no sound from the stereo, and no response occurred when we tried to adjust the volume. However, the volume shown on the navigation did change, so we adjusted the playback mode to CD playback, but there was still no sound. We asked the customer about the car's history. The customer reported that no such problems have happened before. The vehicle was once painted outside, and there was no other maintenance. Observing the navigation, I found that it had an additional installation, but the customer had no problem using it before. After reading the other functions of the navigation, there was no abnormality detected.
Considering that the original multi-disc CD player of the car was replaced with a navigation system, and the modified navigation did not have a self-diagnosis function, there was no way to retrieve the fault code. According to the fault phenomenon, it was suspected that the fault occurred due to the following reasons: (1), there was a problem with the navigation; (2) the power amplifier was faulty; (3) there was a problem with the wiring; (4) there was an internal short circuit in a speaker; (5) there was a problem with the signal line from the CD player to the power amplifier.
Considering that the post-installed navigation had been operating properly until now, and other displays and functional operations were normal except for the sound that did not work, there is little probability of navigation failure, so it was decided not to disassemble and inspect the navigation until other possibilities were ruled out. Next, we checked see if there was a problem with the speaker, because two situations would cause the whole car to have no sound. The first is that a speaker has an internal short circuit The second is that there may be a short circuit in the line of the speaker, causing the entire audio system to fail.
Next, we unplugged all the audio plugs from the power amplifier. After that, we used a multimeter to measure the terminals of the corresponding speaker plugs. It was found that the lines of the speaker itself were not grounded with the body, indicating that the lines of the speaker itself were not abnormal. Considering that the vehicle had not been reshaped or cut, it was suspected that the possibility of problems inside the speaker was relatively low. Thus, we focused on checking the power amplifier itself. We looked the appearance of the power amplifier. The casing was rusted to a certain extent. We opened the casing no trace of water inflow was found. Once again, after reinstalling, the fault remained the same, and no new responses appeared. Then, we decided to check again whether the power supply and grounding of the power amplifier were good. According to its circuit diagram (as shown in Figure 2), it was found that the voltage between the No. 1 terminal +B of its plug P27 and the grounding iron was 8.06V (as shown in Figure 3). There was an obvious abnormality. The voltage between the No. 3 terminal +B2 and the grounding iron was 12.6V, and there was no abnormality. Could it be that our measurement was not accurate? We re-measured and found that the voltage of No. 1 terminal was indeed abnormal. After careful observation, it was found that the terminals inside the plug had been rusted and broken and had green rust, as shown in Figure 4.
After reprocessing the No. 1 terminal and connecting it again, the sound was back to normal. Later, we asked the customer why the plug would be wet. The customer told us that the rear fenders had been painted, and it was suspected that the water had entered unknowingly, which caused the failure.