KORG M500 "Micropreset"

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KORG M500 "Micropreset"

Postby oryjen » Mon Jan 26, 2009 9:43 pm

Hi there!
My M500 has a problem: The 2 grey SYNTHE1 and SYNTHE2 buttons don't work anymore.
I opened the little beastie and had a look on the schemes, but some transistors aren't referenced but just marked "selected".
I'd like to replace TR27, TR29, TR30 and TR31, cause I don't see another possible failure on this point.
My KORG35 chips are OK.

If you own one, could you please take a look at those transistors and tell me their references? (use a lens to read on the flat side).
You'll just have to remove the 4 screws on the bottom, just under the control panel box.

Here are the location of the transistors, blue marked. They're easy to find, because of the twin brown marked KORG35 chips proximity:

Image

Thanx a lot guys!
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Re: KORG M500 "Micropreset"

Postby oryjen » Tue Jan 27, 2009 3:01 pm

Pleeeeeeeze! [-o<
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Re: KORG M500 "Micropreset"

Postby xpander » Tue Jan 27, 2009 7:50 pm

you're in luck - i have the day off & i'm in my studio.


your schematic actually shows what on my circuit board is named (from top to bottom) 27, 26, 31, 30.

29 is above 26, slightly to the left- you can see its location on your schematic.

here are the printed names. the (L) is actually the letter L in a circle.

tr29: C945(L) K7Y

tr27: C945(L) K7Y

tr26: C945(L) K7Y

tr31: only C945 is visible- the rest is covered in blue paint

tr30: C945(L) K7Y

incidentally, mine is in similar shape- although it seems like a contact problem- it's one of the two large-scale projects i have on the backburner, the other being a clean-out of the goo on my Opus 3.
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Re: KORG M500 "Micropreset"

Postby oryjen » Tue Jan 27, 2009 8:50 pm

:shock: All mine are 2SC945 too...
I inverted the 2 KORG35 chips, replaced C44, C45, C48 and C49, and unsolded and checked TR27, TR29, TR30 and TR31.
Now I can't imagine the trick any more...
My selector buttons work perfectly...
SO WHAT?
Seems like if there was a way out to ground somewhere around the KORG35#1 chip....

Please come back and tell me if you find something.

Thanks a lot.
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Re: KORG M500 "Micropreset"

Postby oryjen » Tue Jan 27, 2009 11:56 pm

HANG ON, FOLKS!
If anyone uses one perfectly working, I'd be really pleased to know what they see with an oscilloscope on the negative poles of C44 and C48...(just near to the previously mentionned transistors), just in SYNTHE1 and SYNTHE2 cases.

Thanx! :)
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Re: KORG M500 "Micropreset"

Postby hfinn » Wed Jan 28, 2009 4:16 am

I don't believe you can test transistors and capacitors in circuit...
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Re: KORG M500 "Micropreset"

Postby oryjen » Wed Jan 28, 2009 7:07 am

Of course you can't, but if you understand how the circuitry works and what you may obtain on certain points of it, you may conclude some things about some components , huh?
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Re: KORG M500 "Micropreset"

Postby xpander » Wed Jan 28, 2009 10:09 am

do you have link to legible schematics? i just have the blurry version from korganalogue.net.
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Re: KORG M500 "Micropreset"

Postby bigbadbarns » Wed Jan 28, 2009 10:32 am

Ahh, no way - I bought my friend a MicroPreset for his 21st, same problem. Synthe 1 & Synthe 2 don't work. Which is a shame, because they sound good from demos I've heard, and they are (from memory) the only ones with the simple attack/decay controls.

Unfortunately I understood NONE of what was said above, and I doubt he will either. But, if you guys know what the deal is, I'd love to hear it in laymans terms (or in terms that I can at least describe to the dude who has had it for the last 6 months (supposedly) to fix it.
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Re: KORG M500 "Micropreset"

Postby oryjen » Wed Jan 28, 2009 3:12 pm

Sorry :oops: my poor English remains from school years, 30 years ago...
Perhaps was it not clear?
I wanted to know the type of 4 transistors to be sure mine were genuine.
Then I wanted to know how the current looked on 2 capacitors...
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Re: KORG M500 "Micropreset"

Postby oryjen » Thu Jan 29, 2009 9:04 am

So, any oscilloscope?
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Re: KORG M500 "Micropreset"

Postby Zonkout » Fri Jan 30, 2009 12:19 am

I have had the same problem with TWO M500's!
The first I gave away and the second I had fixed. The culprit was leaking capacitors that had broken traces on the board. Now which caps they were I don't remember, but it should be visibly obvious.
Great sounding synth, once you get it going.
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