Ibanez AD-80 blown by incorrect polarity

[mrsuspend]

I've been offered to buy an AD-80 which is not working after the owner connected it to the wrong polarity.
I'm hoping it's fixable but I'm not quite sure what parts of the circuit is most likely to have blown. The voltage regulator seems like a likely victim though?
http://experimentalistsanonymous.com/diy/Schematics/Delay%20Echo%20and%20Samplers/Ibanez%20AD80.pdf

Obviously I'll have to go through it properly if I buy it, I'm just trying to assess the probable damage as it will reflect of the price I'll offer. So any guesses welcome! 

Thanks!
/Magnus

[Scruffie]

Well the polarity protection diode would hopefully have died first, an easy replacement, then probably the voltage regulator if it was left plugged in for long enough and then well anything after that if it went that far, doubt it did though.

[R.G.]

Get a look at (or a digital picture of) the protection diode inside the box.

If it looks normal visually, chances are it's merely shorted, and can be fixed simply as you note.

If it looks burned, they may have not just connected wrong polarity, but connected a low-voltage AC power supply to it.  This has become common with the rise of digital effects which use 9Vac wall warts with the same plug as 9Vdc supplies. An AC supply first burns the protection diode, then starts killing other parts. There's no good way to estimate what has been killed if it was an AC supply that killed it.

[nexekho]

This has become common with the rise of digital effects which use 9Vac wall warts with the same plug as 9Vdc supplies.

Out of interest, why do they use 9V AC?

[R.G.]

Generally to get more low voltage DC power than is commonly available from DC wall warts.

The effects that use this approach tend to be digital effects with a need for several hundred milliamperes of DC at 5V or 3.3V. They get this by taking in the 9Vac, rectifying and filtering it, and then using either a linear (rare) or switching stepdown converter to make the actual DC for the circuits.

[nexekho]

Generally to get more low voltage DC power than is commonly available from DC wall warts.

The effects that use this approach tend to be digital effects with a need for several hundred milliamperes of DC at 5V or 3.3V. They get this by taking in the 9Vac, rectifying and filtering it, and then using either a linear (rare) or switching stepdown converter to make the actual DC for the circuits.

Ah, thanks!  It just seemed odd to be putting AC into an all digital little DSP.

[mrsuspend]

Thank you for your good advice, apparently he inadvertently switched polarity on his regular power supply (those switchable plugs...) so it got a dose of -18 volts (so to speak).


/Magnus

[SteveFromBerlin]

Any news? Did you find the mistake?

[mrsuspend]

It turned out to be just the blown diode, I replaced it and all was well.

/Magnus