Sony SB V3000 lost input audio L?
 

Hello everyone. My Sony SB V3000 audio-video selector lost the left audio channel at input 4. Thinking it could be the usual broken soldering on the connector pin, I redid the soldering and checked with the tester that the signal fed to the pin reached at least the first 10uF - 50V capacitor placed immediately above. The signal reaches the condenser but by directing it to any other of the 5 connected outputs (including the scart) the left audio channel is missing (on all devices connected to the outputs the vu meters show the audio level only on the right channel, the left remains stationary) . I also noticed that by setting the audio output to "mono" with the appropriate button on the front of the switcher, to duplicate the right channel on the left on the outputs, no effect is obtained: arriving at the other devices there is always and only the right channel. At this point I believe it is an electronic problem which, however, I am not able to identify precisely. Has anyone had the same problem with this selector and, if so, how did they solve it? Thanks to everyone and a cordial greeting.

From your description it seems like the problem is downstream of the mono switch.