My Sony boom headset left ear side is not functioning can it be fixed

Hi,

Yes most probably it can be fixed

There is either a faulty connection on the "tip" connector of the plug, a fractured wire (usually where the cable leaves the plug or where the cable enters the earphones, a faulty connection on the speaker or a faulty speaker.

Here is a video that shows how to dis-assemble a MDR ZX110 (which should be close enough to your model to be relevant).

Use an Ohmmeter to first check that the speaker is OK (connect directly across the speaker terminals) then if the wires seem to be soldered correctly onto the speaker you need to connect one Ohmmeter test lead to one speaker terminal and the other Ohmmeter test lead to either the "tip" of the plug (or the "sleeve" if it is the return connection)

If you cannot prove continuity between the speaker and the plug you may have to cut the cable about 2" from where it leaves the plug, strip the sheath and the wires and then test between the speaker and the cable end to prove continuity. It there is continuity then the problem is in the plug and it will have to be reterminated (with a new plug).

Since the right speaker still works, strip the wires coming out of the plug (remember their colours) and then use the Ohmmeter to find out which wire goes to which plug connector. The right speaker connects between the "ring" and the sleeve"