STK499-070

The STK499-070 is a power amplifier module manufactured by the Sanyo Corporation. In the Kenwood KR-V5090, there are two of these modules, and troubleshooting a faulty one is fairly straightforward in most cases. As you can see from the pinout diagram, pin 15 and pin 16 are the audio power output pins. These output lines usually have some additional circuitry for over-current detection such that high DC voltages from these pins generate a signal to indicate that the module is short. The system then prevents the loudspeaker protection relays from engaging, and causes the system to power down and go into standby mode.

One way I troubleshoot a faulty module is to connect probes to pin 15 and 16, and if they register large DC voltage swings during initial start up, then that is a clear enough clue that the module will require replacing. In some cases, if the system is slow to react, then the current sense resistors will go open. In this circuit they are R213 and R214 (0.22 Ω), and if they are open, then that too indicates that there may have been a short in the speaker terminals. Although these are the two main clues, there may be other issues such as open circuits, which may be more difficult to diagnose.

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