FIXED: Yamaha RX-700: loud pop from the left speaker during shutdown
Hello all,
I have Yamaha RX-700 amplifier from the eighties. The device has a common "soft start / shutdown system" that should prevent pops from the speakers during startup and shutdown. For an unknown reason this feature is not working properly anymore during shutdown: when the relay cuts power from the speakers, a loud pop (or more like a bang) is heard from the left speaker (and left headphone speaker). Turning volume knob to zero before shutdown does not help.
I called to a repair guy but he was not even interested to look the device because he claims there's too many possible causes to this phenomenom so it would probably be costly and therefore not recommended.
I'm quite a noob in electronics so I have no clue what to do. Nonetheless I measured the left channel speaker output terminal several times with multimeter and got something like +2V spike. However, my meter resolution is only 3 samples per second so I probably didn't get max value.
I also measured some voltages from the PCB and noticed that just when the relay cuts power from the speakers, the voltage jumps suddenly from 0 to 52-53 volts on both channels and then starts to fade back to 0V. Is this normal?
I also tried to measure the power supply voltages. From the middle pin I got 65 VAC although this goes directly to the "ground" or "neutral" collector on the PCB. Is this normal? Other pins give me 90VAC and 40VAC.
If I shutdown the device from the main power switch, there's no bang from the speaker even though the shutdown sequence should be the same: first the power-switch-relay cuts power from the protection circuit, then the speaker relay cuts power from the speakers. Or that is what I think is happening.
The simplest fix to this issue would be to press the "speaker select button" to deactivate the speakers and then shutdown the device but I don't like that.
Any ideas what to do?
Hello all,
I have Yamaha RX-700 amplifier from the eighties. The device has a common "soft start / shutdown system" that should prevent pops from the speakers during startup and shutdown. For an unknown reason this feature is not working properly anymore during shutdown: when the relay cuts power from the speakers, a loud pop (or more like a bang) is heard from the left speaker (and left headphone speaker). Turning volume knob to zero before shutdown does not help.
I called to a repair guy but he was not even interested to look the device because he claims there's too many possible causes to this phenomenom so it would probably be costly and therefore not recommended.
I'm quite a noob in electronics so I have no clue what to do. Nonetheless I measured the left channel speaker output terminal several times with multimeter and got something like +2V spike. However, my meter resolution is only 3 samples per second so I probably didn't get max value.
I also measured some voltages from the PCB and noticed that just when the relay cuts power from the speakers, the voltage jumps suddenly from 0 to 52-53 volts on both channels and then starts to fade back to 0V. Is this normal?
I also tried to measure the power supply voltages. From the middle pin I got 65 VAC although this goes directly to the "ground" or "neutral" collector on the PCB. Is this normal? Other pins give me 90VAC and 40VAC.
If I shutdown the device from the main power switch, there's no bang from the speaker even though the shutdown sequence should be the same: first the power-switch-relay cuts power from the protection circuit, then the speaker relay cuts power from the speakers. Or that is what I think is happening.
The simplest fix to this issue would be to press the "speaker select button" to deactivate the speakers and then shutdown the device but I don't like that.
Any ideas what to do?
Last edited: