I had another thread for the amplifier component of a mini system that had some issues. those are resolved via replacement of the 4 power supply filter caps.
The pre-amplifier of this system also has a problem. It outputs a powerful ~120hz hum. The amplifier has a spectrum analyzer with a 125 hz position and that's where it lights up. On the pre-amp is an equalizer. If I move that slider or one on either side up the spectrum analuzer at 125hz will just about peg at the top and this is audible through the speakers.
This system uses a proprietary interconnect cable. Using a pair of headphones and some test leads the hum also outputs to the headphones, this noise is definitely originating in the pre-amp. No matter which input of the pre-amp is used only the HUM is output, there is no music that can be heard, only the hum.
the service manual is available here:
https://archive.org/details/manual_B...e/n11/mode/2up
That manual has both the amp (gx) and pre-amp (bx). I'm having trouble with the pre-amp.
The Q21 looks to have been replaced previously. It also looks to have left its mark on the top cover. Not sure if this has anything to do with the problem
Any help is appreciated... not sure where to start.
The pre-amplifier of this system also has a problem. It outputs a powerful ~120hz hum. The amplifier has a spectrum analyzer with a 125 hz position and that's where it lights up. On the pre-amp is an equalizer. If I move that slider or one on either side up the spectrum analuzer at 125hz will just about peg at the top and this is audible through the speakers.
This system uses a proprietary interconnect cable. Using a pair of headphones and some test leads the hum also outputs to the headphones, this noise is definitely originating in the pre-amp. No matter which input of the pre-amp is used only the HUM is output, there is no music that can be heard, only the hum.
the service manual is available here:
https://archive.org/details/manual_B...e/n11/mode/2up
That manual has both the amp (gx) and pre-amp (bx). I'm having trouble with the pre-amp.
The Q21 looks to have been replaced previously. It also looks to have left its mark on the top cover. Not sure if this has anything to do with the problem
Any help is appreciated... not sure where to start.
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