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Briefly disconnected battery causes radio no sound

For safety, I disconnected the negative side of the battery before removing the ignition lock switch, which needed repair by a locksmith.

With the repaired lock reinstalled, everything worked, including the display on my low end Pioneer stereo, although not surprisingly I had to reset the clock. I was happy that my few radio presets were still there.

But there was no sound from the radio, not even faint rumbles. Nothing. Nor was there audio from a CD.

I called Pioneer Electronics tech support, asking what setting on the stereo unit might have muted the audio. The tech seemed clueless, said there was nothing like that on this stereo, only said the radio needs a bench test.

The only local car audio shop, which has a dismal reputation, suggested that the issue might be with the amplifier. It’s not certain that my Sienna has an amp, but I have a vague recollection that it might, from the time I replaced the 18 year old stock Toyota radio with the Pioneer stereo, less than two years ago.

The car audio tech suggested that I try disconnecting the battery again for about 10 minutes, saying that it might “reset” the amplifier. That sounded bogus, but being simple, I tried it anyway. No change.

How can simply disconnecting and reconnecting the battery cause a problem like this? I don’t believe that the simple process of removing the ignition lock (with the battery disconnected) is the direct cause, I didn’t get close to the stereo or deep under the dash, touch anything other than the switch, or pull on any wires.

I’m stumped. Can anyone shed light on this?

I’d accept that there may be a fuse problem, but nothing in the car is affected other than sound. If there’s a separate circuit just for the amplifier, it’s not marked on the interior fuse panel - there’s one for radio only, but again, the unit display and controls all function. Could there be a fuse under the hood for just the amp?

This Sienna is the LE model, though it does not have special features like the power sliding door, or leather seats, and the stock radio did not have a CD slot, so I don’t know if that’s any clue about presence of an amplifier.

Thanks for any advice.