Eliminating popping sounds in the Panasonic SA-XR15

ID: 237246

Description: The aforementioned AV Control Receiver...

Steps:

1. Before opening the device, all cables, especially the power cord, must be disconnected!
2. Next, remove the device cover. To do this, remove three black Phillips screws on the back (top) and two silver Phillips screws on each side.
3. The cover can now be slightly spread and lifted off.
4. You can now see the switching power supply with a protective cover on the left and the amplifier unit with the large aluminum heat sink on the right. To the right of the heat sink, the DSP unit is mounted piggyback above the amplifier unit. This must be removed. Only then can you reach the components located underneath.
5. The DSP unit is released by unscrewing the single fixing screw on the top right. Then it can be lifted off very, very carefully. Attention: On the underside of the DSP board, there are two blade connectors, and the board is additionally secured by two polyamide standoffs.
6. The polyamide standoffs have two barbs. These must be carefully pressed in with needle-nose pliers to remove the board. Only then can the PCB be moved upward. The shielded cables on the upper narrow side can remain plugged in. The board can be set aside safely.
7. Once the DSP board is removed, we can identify the voltage converter IC612 on the amplifier board, top right. This generates two additional voltages from +5V (pin1), namely +3.3V (pin4) and +2.5V (pin5).
8. Below the pin row of the IC612, two 22uF 10V electrolytic capacitors are mounted: C227 and C228. These must be replaced.

9. The two electrolytic capacitors C227 and C228 are being replaced.
10. The old electrolytic capacitors, usually round types with a small insulating washer at the bottom, are carefully desoldered. The pads are cleaned with desoldering wick. Flux residue can be removed with a Q-tip and methylated spirits.
11. The new electrolytic capacitors are installed in the corresponding locations. Caution: Be sure to observe the correct polarity. In some versions (as seen in the photo), the positive pole is marked!
12. The DC to DC converter operates at a very high switching frequency. For this reason, only capacitors with low ESR should be used! ESR stands for Equivalent Series Resistor. Only these can handle the high switching frequencies.

13. As usual, everything is reassembled in reverse order.
14. First, carefully place the DSP board back into its original position above the amplifier unit. The polyamide mounts help with precise positioning. Then, connect the connectors and finally reinsert the single mounting screw.
15. Before replacing the cover, the success of the repair can be verified by very carefully powering on the device: connect a speaker to one of the main outputs. Plug the power cord back in. The red LED should light up.
16. Press the power button; the LED will turn off—and hopefully, no more popping sound will be heard. If you select the FM tuner as the input, you can also listen to the radio. If necessary, connect a small makeshift antenna to the tuner input. A piece of wire is usually sufficient.
17. If you have an oscilloscope available, you can check the two DC voltages, +3.3V and +2.5V, at IC 612. Under no circumstances should you bridge pins 4 and 5 of IC 612 with the probe tip. Both DC voltages should be measurable—without any visible superposition of high-frequency oscillations.
18. Anyone who is inexperienced with using a probe tip and ground clip should definitely stick to just replacing the capacitors.
19. If the brief tests were successful, unplug the power cord again and place the top cover onto the device. Once all seven screws have been driven back into their correct positions, we have completed a hopefully successful repair. In other words: we are finished.