Hello,
Last week I received the new components I ordered from Mouser.
I worked on replacing several components, including suspect resistors, checking various transistors, and replacing the four power output transistors in models MJ21193G and MJ21194G.
The result is that after adjusting the unit according to the manual specifications, I got both channels working.
It took me a while to find a fault that was causing one of the channels not to work (I thought it was a bad solder joint) until I discovered that the red wire connecting the volume and balance control board and the tone board output (red wire) was internally broken.
That said, I now have a stable unit playing in both Class B and Class A modes.
On the other hand, I've encountered two problems.
First, I have a noise with the speakers on but no audio. With audio, the noise is very clear and barely noticeable.
I should mention that the circuit boards are scattered on my workbench and not installed in their respective positions. Perhaps this makes it easier for a nearby signal to be induced, and this won't be a problem once the unit is reassembled and all the protective metal covers are put back on.
For example, when I touch the chassis of the filter board, the noise increases, like parasitic noise, and when I touch the loudness knob, it also increases. Could you confirm if this is the case, check something, or simply re-assemble everything?
The second problem I have is that the device goes into protection mode and activates the relay when I turn the volume up past halfway. When I turn the volume down, the device returns to normal and works correctly.
Could it be due to the replacement of the output transistors that they need to be adjusted to different values than those indicated in the service manual, since they obviously don't have the same characteristics?
Could it be that I need to modify the value of one of the resistors that regulate the operating voltage/power of the output transistors?
Thank you very much as always
Last week I received the new components I ordered from Mouser.
I worked on replacing several components, including suspect resistors, checking various transistors, and replacing the four power output transistors in models MJ21193G and MJ21194G.
The result is that after adjusting the unit according to the manual specifications, I got both channels working.
It took me a while to find a fault that was causing one of the channels not to work (I thought it was a bad solder joint) until I discovered that the red wire connecting the volume and balance control board and the tone board output (red wire) was internally broken.
That said, I now have a stable unit playing in both Class B and Class A modes.
On the other hand, I've encountered two problems.
First, I have a noise with the speakers on but no audio. With audio, the noise is very clear and barely noticeable.
I should mention that the circuit boards are scattered on my workbench and not installed in their respective positions. Perhaps this makes it easier for a nearby signal to be induced, and this won't be a problem once the unit is reassembled and all the protective metal covers are put back on.
For example, when I touch the chassis of the filter board, the noise increases, like parasitic noise, and when I touch the loudness knob, it also increases. Could you confirm if this is the case, check something, or simply re-assemble everything?
The second problem I have is that the device goes into protection mode and activates the relay when I turn the volume up past halfway. When I turn the volume down, the device returns to normal and works correctly.
Could it be due to the replacement of the output transistors that they need to be adjusted to different values than those indicated in the service manual, since they obviously don't have the same characteristics?
Could it be that I need to modify the value of one of the resistors that regulate the operating voltage/power of the output transistors?
Thank you very much as always
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