Hi All,
I am sitting on a few amps that have one channel working and the other one not. If I press mono on some of these, audio is there on both channels.
What would that indicate you? Issue in the pre-amp portion or one of the output StKs (or transistors) blown? Something else?
I am sitting on a few amps that have one channel working and the other one not. If I press mono on some of these, audio is there on both channels.
What would that indicate you? Issue in the pre-amp portion or one of the output StKs (or transistors) blown? Something else?
Obviously both power amp channels are ok, only the circuitry before the mono switch (or the switch itself) is implicated.
I'm new to repair and diagnosing so will not give technical advice but just logical thoughts.
If you get volume in both speakers then the output section probably works fine for both.
So it probably will be something between the rca/jack input and the preamp, perhaps before the switch where the signal gets summed and sent to preamp. Do you have a schematic/ name and model of the amp? Thiss will be super useful to when some of the audio gods read the thread.
I AM NOT ADVISING THIS, since I don't know if it is a good practice or if i am a fool, but i connected two leads to an old trash speaker i don't mind killing, connect the negative to the negative speaker binding post/common ground and with the + i start probing the various pins on the audio signal path, so form the input +, to the volume potentiometer, to the pre etc. to try and figure out where the sound stops. Sometimes i get loud pops which freak me out so i dont know if i am doing something prohibited.
I'm sure there is a better way to find out where the signal disappears though so i'll leave it to the experts and i'll keep following this cos it's an interesting thing to diagnose
If you get volume in both speakers then the output section probably works fine for both.
So it probably will be something between the rca/jack input and the preamp, perhaps before the switch where the signal gets summed and sent to preamp. Do you have a schematic/ name and model of the amp? Thiss will be super useful to when some of the audio gods read the thread.
I AM NOT ADVISING THIS, since I don't know if it is a good practice or if i am a fool, but i connected two leads to an old trash speaker i don't mind killing, connect the negative to the negative speaker binding post/common ground and with the + i start probing the various pins on the audio signal path, so form the input +, to the volume potentiometer, to the pre etc. to try and figure out where the sound stops. Sometimes i get loud pops which freak me out so i dont know if i am doing something prohibited.
I'm sure there is a better way to find out where the signal disappears though so i'll leave it to the experts and i'll keep following this cos it's an interesting thing to diagnose
Thanks for this, I think thats not a bad idea to trace the signal that way. I can as an old test gear a probe with a little speaker in it that was probably used for this kind of purpose. Alternatively I can use my scope and put a test signal (e.g. 1 khz) to an input.
The amp in question is a JVC SR-201.
https://elektrotanya.com/jvc_jr-s201_sm_en.pdf/download.html
Service manual scan is in excellent quality.
The amp in question is a JVC SR-201.
https://elektrotanya.com/jvc_jr-s201_sm_en.pdf/download.html
Service manual scan is in excellent quality.
That was the first thing I did. Some of the switches were not latching, or stuck latched. They got a good bath in contact cleaner before I then had to remove them to fix the latching mechanism. There was quite a bit rust on springs. If there is still a contact issue not sure if more deoxit can fix it.
Vintage audio gear has switches and relays, mechanical things to route signals. They become intermittent with oxides on the contacts because there is not enough "wetting current" to keep them healthy. A radical solution might be needed.
.. https://en.wikipedia.org/wiki/Wetting_current
.. https://melbmcu.weebly.com/funny-switch-behaviour.html
I hope not 🙂
The Tape 1 input works on both channels. But the inputs on the 90 degree angled switch bar have all this issue. One of them is "AUX" which I used before. These switches actually havent been cleaned before. I was focused on the horizontal buttons on the bottom of the case that were partly stuck.
But cleaning them did not lead to any improvements. So this seems to be a genuine electrical issue - as all of these input show the same behavior.
The Tape 1 input works on both channels. But the inputs on the 90 degree angled switch bar have all this issue. One of them is "AUX" which I used before. These switches actually havent been cleaned before. I was focused on the horizontal buttons on the bottom of the case that were partly stuck.
But cleaning them did not lead to any improvements. So this seems to be a genuine electrical issue - as all of these input show the same behavior.