Get a voltmeter on continuity and check all 3 of the leads on Q16 to make sure they have continuity to the next component on the board. Just visually follow the traces to see where they go. Note the traces can be on the top of the board or the bottom, or even both sides. You need to have good solder joints. It is very possible whoever soldered in the new transistor did not get a good solder connection to all three legs of the transistor.