techknight said:

Any time the output transistors fail, the TL071 has to be replaced with it. 

as for testing transistors, most of the sites do tell you to check it in ohms. Those sites suck and likely dont have much electronics experience whatsoever. 

The best way to do this is using diode check on your DMM. on an NPN, youll get .4XX to .6XX between base to emitter, and base to collector. positive on base. Reverse the leads, you get nothing. Also C to E you get nothing. 

PNP is the opposite. Black lead on Base, otherwise you get nothing. 

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I guess you're "techknight" for a reason.  I replaced the op-amp and once again the sound is working loud and clear!  Thank you!  I have searched these forums over and over looking for people whose SE/30s had similar symptoms to mine, and haven't found any that quite matched.  Hopefully this thread helps someone else.  So to summarize what I did to fix this issue:

- after a successful recap, the sound mysteriously faded to static (completely unrelated to the new ROM chip I happened to install at the same time)

- performed continuity tests between capacitors (c1 - c10) and the Sony sound chips (everything checked out)

- used a DMM (digital multimeter) on diode test mode to test the Q1 NPN and Q2 PNP transistors; Q1 was in doubt

- I replaced Q1 (didn't fix the problem)

- I then replaced the op-amp chip (UA9 on the board)

That did the trick!  No more static!  The power-on chime is loud and clear!