techknight said:

if the headphone jack works fine, then you need to check the op-amp and transistor pair next to the sony chips. That drives the speaker. 

Also keep in mind the speaker amplifier gets its signal from a reed finger in the headphone jack, so if the jack is corroded slightly, the speaker may or may not work or intermittently. 

Click to expand...

So I think I've narrowed the problem down to the Q1 NPN transistor.  Comparing this board side by side to one of my working boards, I get no resistance readings between emitter (-) and base (+) nor between collector (-) and base (+) on my broken board.  The same readings on my working board look normal (numbers in the MOhms).  The Q2 PNP transistor tests the same on both boards. 

I'm not familiar with the component specs.  The lettering on it says "1A."  I searched for 1A surface mount NPN transistors, and found some.  Unfortunately they come in 10K, 22K, and 47K varieties (on Amazon).  Do you know the kind of transistor I'll need?  Are there different transistors that might be better?

Thanks!