Not dead... but really really quiet. (help wanted)

[theshame]

I picked up a crappy black blob keyboard (Gran Prix KB810) awhile ago and it was working fine. I was bending it and found some really easy pitch bends when all of a sudden it died. I think the alligator clips connected to the batteries were touching positive to negative while connected to the keyboard.

I fired it up later and noticed that it is working correctly, all keys function, demos play, but the sound is extremely faint. I can only hear it with my ear pressed against the speaker. I've tried wiring up another (smaller) speaker in parallel with no positive results. The voltage across the speaker is somewhere around .02mV.

I figure I fried the amp part of the circuit. However, there are no chips on the board, so I don't know what to try and replace. Nothing looks burnt out. Any ideas? My fear is that something in the blob is done for.

[Dylan]

Does it sound kind of distorted too? Kind of like it's clipping? That happened to one of my favorite bends:

Circuit Bent Animal Keyboard

Sadly I never got it back : ( Have you tried playing it through a jack?

[Sam_Zen]

The voltage across the speaker is much too low. I'm afraid you blew up the output amp.
Maybe you can find a point at the input of this amp, so you could use it as a Line output.

[the_zombiest]

does the signal pass through any other components (transistor, electrolytic cap) before entering the speaker?
Sometimes you just need to replace one or the other... or both to have it come back to life.

[Sam_Zen]

Good idea about the electrolytic cap.
Especially tantalum ones (the single coloured 'drops') are very versatile with wrong voltages.

[Gordonjcp]

It's unlikely you'll see a tantalum bead used as the speaker output cap.

You could try stuffing the output of the instrument into some kind of high-gain amplifier like a fuzzbox.  It will be noisy and distorted, but maybe that's useful to you.