Hi, this is my first post. I have an amateur's knowledge of electronics and have been modestly successful in repairing old audio gear using a multimeter and a soldering iron.
I'm working on a Yamaha R-90 receiver that stopped outputting sound after the cables attaching an iPod to it were pulled from the AUX jacks while the unit was powered up. The owner heard a loud thump when the cables were pulled. I have determined that the speaker relay does not close when the unit is powered on. If the relay is manually closed, the unit outputs sound through headphones. I did not check it with speakers hooked up, but I assume it will output sound there as well.
A close visual inspection revealed a zener with blackened leads. No other components have blackened leads. I pulled it to test it for resistance in both directions with the aim of replacing it if I got a bad reading. So I tested it using a digital meter that has scales of 200, 2K, 20K, 200K and 2M. The 2K scale has a diode symbol below the 2K designation. Using that scale I get a reading of 715 ohms in one direction and open in the other. This seems like a normal reading, but I am not sure. I then noticed using a magnifier that it had no markings whatsoever. The service manual/schematics seem to be not readily available.
The zener may be good and it may be bad. It could also be that some other component is bad, sending too much current through the zener.
Does anyone have any thoughts on what stress is placed on the circuitry of an audio amp when the cables of an input device like an iPod are yanked while the power is on? And where might I find the schematics for this unit?
Thanks for reading,
Jack
I'm working on a Yamaha R-90 receiver that stopped outputting sound after the cables attaching an iPod to it were pulled from the AUX jacks while the unit was powered up. The owner heard a loud thump when the cables were pulled. I have determined that the speaker relay does not close when the unit is powered on. If the relay is manually closed, the unit outputs sound through headphones. I did not check it with speakers hooked up, but I assume it will output sound there as well.
A close visual inspection revealed a zener with blackened leads. No other components have blackened leads. I pulled it to test it for resistance in both directions with the aim of replacing it if I got a bad reading. So I tested it using a digital meter that has scales of 200, 2K, 20K, 200K and 2M. The 2K scale has a diode symbol below the 2K designation. Using that scale I get a reading of 715 ohms in one direction and open in the other. This seems like a normal reading, but I am not sure. I then noticed using a magnifier that it had no markings whatsoever. The service manual/schematics seem to be not readily available.
The zener may be good and it may be bad. It could also be that some other component is bad, sending too much current through the zener.
Does anyone have any thoughts on what stress is placed on the circuitry of an audio amp when the cables of an input device like an iPod are yanked while the power is on? And where might I find the schematics for this unit?
Thanks for reading,
Jack