Sony STR-DE400 Protect Repair

The STR-DE400 has the ability to protect the expensive components from damage by automatically switching OFF in the event a circuit anomaly. Switching ON the amplifier usually produces a "click" sound, which is the primary relay engaging. Providing there are no short circuits, the microcontroller then engages a second relay, which connects power to the main (large) transformer. If there is electronic damage to the amplifier, then the second click will be absent, and instead the microcontroller displays "PROTECT" on the front display.

The audio power output stage of each channel has additional circuitry for current detection and power protection. These circuits usually flag their information to the main microcontroller on the front panel. In the event of electrical conditions being outside normal parameters, the microcontroller prevents the relay from energising thereby cutting power to the amplifier circuits. In these situations, it is better to disconnect all the speaker wires and seeing if the condition persists. If the error persists, then the amplifier will require electronic repair by a qualified service engineer.

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