Service manual on elektrotanya just describes the test function. Triggering
one phones socket sw, triggered in isolation, cuts the speaker ; the other
,triggered in isolation, attenuates marginally from eg 1.58V ac over speaker
to 1.2 V . But in normal use , the speaker cut sw takes precedence and both
stereo and mono jacks cut the speaker.
Now I've replaced the socket, foreign object landed insid and then rear of
the Jalco got mangled and pushed out