So this lovely little receiver has been giving me lots of trouble and I can't really find anyone else who has done a restoration thread on this receiver so I thought I would.
After all this is a very nice little receiver and I would love to see more of these up and running.
When I first got the amp it turned on fine. The audio was distorted and very quiet.
After replacing every capacitor all of these problems remained.
4
My next step was replacing the output transistors as it seemed likely these must have failed.
Replacing these is extremely hard!! Mostly because you need like 5 hands in order to hold the transistor soldering iron, screw driver, insulator and all that stuff. Very frustrating but doable if patient enough.
Once I finished replacing these transistors the audio distortion was gone but the amp was still very quiet!
Ahaa! Progress at least.
My next step was to check every single resistor. However I knew that the carbon composite resistors were most likely to fail. So I checked these first.
Upon checking the four carbon composites that should be measuring 330ohm they measured 800ohm on 2 of them and the 1k ohm on another and one even measured 1.2mohm.
Ahhaaaa!! There is the problem.
I circled all of the resistors that need to be replaced in this picture. There is another one hiding under the power cord which I bundled up around the transformer.
I will get to replacing these resistors and see how the amp works after that. Then I will bias the amp and hopefully it will be ready to go into my collection
.
So in the future if anyone stumbles upon this thread when going to restore their fisher 122 I would recommend re-capping and replacing the carbon composite resistors as they tend to drift out of spec. In solid state amps they may do so even more.
This amplifier stumped me for almost a month and it was very frustrating when I couldn't find the problem.
Hopefully this will help some people who are working on this same amp.
To be continued.
After all this is a very nice little receiver and I would love to see more of these up and running.
When I first got the amp it turned on fine. The audio was distorted and very quiet.
After replacing every capacitor all of these problems remained.
My next step was replacing the output transistors as it seemed likely these must have failed.
Replacing these is extremely hard!! Mostly because you need like 5 hands in order to hold the transistor soldering iron, screw driver, insulator and all that stuff. Very frustrating but doable if patient enough.
Once I finished replacing these transistors the audio distortion was gone but the amp was still very quiet!
Ahaa! Progress at least.
My next step was to check every single resistor. However I knew that the carbon composite resistors were most likely to fail. So I checked these first.
Upon checking the four carbon composites that should be measuring 330ohm they measured 800ohm on 2 of them and the 1k ohm on another and one even measured 1.2mohm.
Ahhaaaa!! There is the problem.
I circled all of the resistors that need to be replaced in this picture. There is another one hiding under the power cord which I bundled up around the transformer.
I will get to replacing these resistors and see how the amp works after that. Then I will bias the amp and hopefully it will be ready to go into my collection
.So in the future if anyone stumbles upon this thread when going to restore their fisher 122 I would recommend re-capping and replacing the carbon composite resistors as they tend to drift out of spec. In solid state amps they may do so even more.
This amplifier stumped me for almost a month and it was very frustrating when I couldn't find the problem.
Hopefully this will help some people who are working on this same amp.
To be continued.