I am working on repairing a 1970s Magnavox stereo console. The Left channel works perfect, but the right channel is dead at the speaker. This happens in all modes (Tape, Phono, FM Stereo). Now, I do have audio from the right channel via the "Tape Record" output, so this confirms the problem is in the right channel AF and Output amp? I also tested the speaker itself. I attached a schematic of the Right channel: AF and Output.
In addition to a recap, I found that R101 and R107 were both open (see arrows). I replaced R101 and R107, but they both become very hot. MUCH MUCH hotter than the left channel. Also, transistors Q21 and Q22 became very warm so I removed power. Q21 and Q22 both test fine (even after the heat). The voltages at Q21 and Q22 were both pulled down low. So a ton of load is being put on the output transistors and R101, R107. The left channel also had low voltages, but no heat. I believe the problem in the right channel was pulling the whole power supply down, too.
I am just now learning about amps, so forgive me for using terms incorrectly. I believe R101 and R107 have to do with the push pull system of Q22 and Q21? I read somewhere that you can run into oscillation problems and thermal runaway when this section acts up? I can't find any other bad parts. Tested Q20, Q18 and Q29, all the resistors.. Really looking for some advice.
Thanks.
In addition to a recap, I found that R101 and R107 were both open (see arrows). I replaced R101 and R107, but they both become very hot. MUCH MUCH hotter than the left channel. Also, transistors Q21 and Q22 became very warm so I removed power. Q21 and Q22 both test fine (even after the heat). The voltages at Q21 and Q22 were both pulled down low. So a ton of load is being put on the output transistors and R101, R107. The left channel also had low voltages, but no heat. I believe the problem in the right channel was pulling the whole power supply down, too.
I am just now learning about amps, so forgive me for using terms incorrectly. I believe R101 and R107 have to do with the push pull system of Q22 and Q21? I read somewhere that you can run into oscillation problems and thermal runaway when this section acts up? I can't find any other bad parts. Tested Q20, Q18 and Q29, all the resistors.. Really looking for some advice.
Thanks.
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