Korg microKORG

[squigley]

Hello, I am trying to diagnose and hopefully fix this synth

First, the power is stupid reverse polarity which is probably why I am here..

Immediately after the power jack is an inductor which I removed and tested to be dead shorted (I should qualify that this is a 4 pole inductor with both positive and negative running through it, and all 4 legs are dead shorted).

I continued checking and found a cap to be shorted so I removed it. I then found 2 diodes misbehaving so I removed those.

Things still may be shorted so I don't want to apply any power.

Has anyone worked on one of these before?

[squigley]

I bypassed the questionable input section, and applied 9v directly to the ground plane and positive rail.

It powers up, the audio in 1 and 2 LEDs light up for about 2 seconds, and then go off. That's the only sign of life.

[squigley]

This is all is does, for about 2 seconds.

[squigley]

I found someone on Reddit with the same problem, but no solution :-(

https://www.reddit.com/r/synthesizers/s/2NOUiwO9Hs

[squigley]

I found this which provided some clues..

http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=23125&postdays=0&postorder=asc&start=0

The audio in LEDs coming on just basically indicates that the 5v rail is working.

The issue is that the 3v3 rail is not.

I checked the pwm switching chip and found it to all be shorted and passing 9v straight through :-(

The fet also seems suspect.

And the fuse between the switching chips and the 3v3 circuit is blown.

I applied 3v3 to the after side of the fuse, and all that happed was that briefly one of the switches lit up, and then nothing, except the CPU got hot enough to almost give me a 3rd degree burn.

So it looks like I need to source a replacement CPU, and the 3v3 switching components.

I am hoping that only the CPU got blown, and it protected the ram and flash chips and the DSP etc.

[fzabkar]

FWIW ...

https://elektrotanya.com/showresult?what=microkorg&kategoria=All&kat2=All