Bill, Good point about reminding us that the external speaker works, and
no excessive heating. The series RC on IC audio stages is NOT switched
out, especially when using an external speaker with extra lengths of
cable that provides varying feedback.
The RC is to restrict the high gain IC from taking off at ultrasonic
frequencies in all situations.
Given that you have the problems only with the internal speaker in use,
you have a short or magnetic short in that speaker or the attached
wiring from the speaker jack to the internal speaker. I can't imagine
the coupling cap being switched out if you use the external speaker
either, so that remands us to the internal speaker being at fault.
It may not be as bad as it looks to access the wires going from the
speaker jack to the internal speaker. Check across those terminals with
an ohmmeter when the jack is open, and see if you have a short other
than the low impedance of a speaker coil.
Check also from each wire to chassis ground, in case this set employs a
floating audio output. Expect to see 5 ohms or so for an 8 ohm
impedance speaker. This can vary, so anything over a couple of ohms but
less than the speaker impedance is probably ok across the pair.
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