Hello,
I recently bought locally a Harman Kardon 730 receiver from the 70's. It works flawlessly with the exception of one thing: When I power it down and there is an input to it (meaning into its Auxiliary input from a DAC or another device), it continues to play flawlessly for nine seconds and then it shuts down in another two, but the music is distorted throughout that last period. The volume at which music is played does not have effect on the times described above i.e. It could be very quiet or loud, it always shuts down in 11 seconds. Interesting to note is that If I set it to radio, the receiver shuts down as it should: it takes no more than two seconds. Also, the lamps on the front turn off immediately, so in essence, the phenomenon is observed only when Auxiliary inputs are being used.
I intend to fix this in a month, during spring break and would appreciate if I get some suggestions with regards where and what to look for. I was going to check first for ways the large capacitors within the PS continue to discharge and power the preamp and amp sections. I have attached the service manual which contains all the schematics.
Thanks in advance.
Best
Soundork
I recently bought locally a Harman Kardon 730 receiver from the 70's. It works flawlessly with the exception of one thing: When I power it down and there is an input to it (meaning into its Auxiliary input from a DAC or another device), it continues to play flawlessly for nine seconds and then it shuts down in another two, but the music is distorted throughout that last period. The volume at which music is played does not have effect on the times described above i.e. It could be very quiet or loud, it always shuts down in 11 seconds. Interesting to note is that If I set it to radio, the receiver shuts down as it should: it takes no more than two seconds. Also, the lamps on the front turn off immediately, so in essence, the phenomenon is observed only when Auxiliary inputs are being used.
I intend to fix this in a month, during spring break and would appreciate if I get some suggestions with regards where and what to look for. I was going to check first for ways the large capacitors within the PS continue to discharge and power the preamp and amp sections. I have attached the service manual which contains all the schematics.
Thanks in advance.
Best
Soundork
This is normal. The power supply gradually decays upon power off, and the amplifier distortion goes up.
The tuner dies first, so it just seems that the amp is behaving differently with the tuner playing.
You can verify this by connecting the tape out jacks to another stereo while playing the tuner,
and then turn off the receiver.
I have several of that series of receivers, and they have never needed new power supply capacitors.
They last a very long time.
The tuner dies first, so it just seems that the amp is behaving differently with the tuner playing.
You can verify this by connecting the tape out jacks to another stereo while playing the tuner,
and then turn off the receiver.
I have several of that series of receivers, and they have never needed new power supply capacitors.
They last a very long time.
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Sorry, I didn't think that there is anything wrong with the capacitors in the PS. I just commented that there might be some path through which they discharge and power up the preamp and amp sections for additional 9 seconds after turning the receiver off, which is not normal.
I also gave the example that if in radio mode, the receiver shuts down normally.
Soundork
I also gave the example that if in radio mode, the receiver shuts down normally.
Soundork