dead microkorg

Post by **man-009** » Sat Feb 25, 2012 7:36 am

well matt said,... " OK, got the synth apart and got the board out. Based on inspection with an ohmmeter only, I have a little concern that 9V may have been applied to the CPU/DSP. This is pretty much fatal to them. If you look at the schematics pg 5 there is a MOSFET (F1) - right above the S-8520F33 regulator chip [that got so hot it desoldered.] This F1 acts as a switch, where the gate (G) controls current between the source (S) and drain (D.) This appears to be still intact, I measure a short circuit between the source and drain because there is nothing connected to the gate. The source is connected to 9V. The S-8520F33 regulator is supposed to shut this FET off when the output voltage gets slightly above 3.3V, and turn it back on when it gets slightly below 3.3V. Without the regulator chip to turn it off, it tends to stay on, which would cause the output to go to 9V.

I'll take it to work on Monday and try to connect an external 3.3V supply and 5V supply to the two power rails, and see if it powers up " ...more news soon.

Post by **man-009** » Mon Feb 27, 2012 2:09 pm

we find out today all!..stay tuned if the microkorg comes back to life!

gearfixer · Post by **gearfixer** » Wed Feb 29, 2012 2:31 pm

Did it fire up?

Post by **man-009** » Wed Feb 29, 2012 9:23 pm

soldering gun delay.ordered a new one. should come in today. he is building the regulator kit first, and desoldering the two components. Then he will see if a 5 v supply works. wish him luck!

Post by **man-009** » Thu Mar 01, 2012 6:43 pm

IT'S ALIVE!!!!!

The External 3.3 v regulator and bypassing the fuse ...its alive! It does put sound out!!!!!!
Need to find replacement fuse and a 3.3 volt regulator small enough to fit. he can't test the digitizer - he is still afraid that something isn't quite 100% on the SuperH CPU chip. Needs to run all the self tests first.
not sure how to ID the fuse, needs to do more research - the only marking is '20'. don't want to bypass it - he thinks that was what saved it to begin with.
Voltage regulator - he can't use the little one that he rigged - not efficient. will probably get a TI/National evaluation board and rig it in there.
So it'll still be some time for to figure out the fuse and make the order, and solder it together. still more work..keeping fingers crossed.

Post by **man-009** » Sat Mar 03, 2012 11:54 pm

more news:

"the bigger issue is securely connecting to the main board and mounting the new small converter unit".

getting closer...

Danchenka · Post by **Danchenka** » Mon Mar 05, 2012 2:57 pm

Does the fuse look like a transistor with just two legs? You may need a N20 IC protector. When I thought that I fried my K5000 (shorted two pins when the probe on my multimeter slipped as I was fixing the LCD), an N25 saved it. I replaced it and was good to go. The only marking on that was a 25, so you might have a similar part. Take a look at this site. http://freespace.virgin.net/matt.waite/ ... tector.htm
I got my replacement from RS electronics, but since then I have seen them in some regular electronics shops. They're cheap, but I had to buy a pack of ten from RS and then pay shipping. It may be worth asking if your local shop has one. You might not need to order it.

Anyway I hope you get it working perfectly again.

Post by **man-009** » Tue Mar 06, 2012 4:11 am

my friend matt is working on it in texas. he is keeping me updated. i will ask him. he says he has all the parts ordered that he needs for the fix so it should be soon. thanks.

Post by **man-009** » Wed Mar 07, 2012 5:09 pm

almost fixed!

"I'm going to have to glue gun the new regulator to the PCB. It is probably safer than electronic epoxy because it is removable. I need to keep the wires as short as possible, and this is the best way to do it. So there is always the risk of it getting disconnected. I will try to document what I did so if something deattaches, it can be easily resoldered. The mechanical stuff is what scares me the most."

Post by **man-009** » Thu Mar 08, 2012 3:34 pm

My fried microkorg lives again! So if you use a wrong power supply....remember this..

We can rebuild him..we have the technology! microkorg is that man!...lol thanks matt!
"Ain't pretty, not necessarily mechanically solid, but it works! "..i think it looks bad a*s!

http://imageshack.us/photo/my-images/44 ... 11826.jpg/

So now there is some good info here if you ever fry your motherboard on a microkorg! now whatch everyone buy dead microkorgs!

sknhd69 · Post by **sknhd69** » Mon Mar 12, 2012 3:51 pm

hello, my first post here
greetings from far east [really really far, actually]

my MicroKorg also dead [because of wrong adaptor polarity]
probing IC5 voltage, it turns good [~3.2v] so it's not the problem
luckily, only FU1 is failed...so, simply bypass it for temporary fix...until i bought N20

http://img.photobucket.com/albums/v11/s ... a4f54b.jpg

close up
http://img.photobucket.com/albums/v11/s ... d700fd.jpg

thanks man-009 for making me dare to disassemble microkorg

video --

Post by **man-009** » Mon Mar 12, 2012 8:26 pm

cool. good to know others are getting them serviced!

sknhd69 · Post by **sknhd69** » Tue Mar 13, 2012 4:06 pm

anyway, can i change MicroKorg's polarity to "standard" center-positive?

so, no more fried microkorg because of wrong polarity

Post by **Stab Frenzy** » Wed Mar 14, 2012 3:51 am

Centre positive isn't standard for 9V power supplies, most are the centre-negative type that Boss uses.

Post by **man-009** » Mon Apr 09, 2012 5:01 pm

the dead microkorg is now fully 100% working! thanks to matt and ARM!
now i am doing a mod on the body with new paint and name. pics coming soon!

hint: we can rebuild him, we have the technology!

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