Korg DW8000 issues

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Korg DW8000 issues

Postby Algorithm » Mon Feb 24, 2014 9:29 pm

Hello,
Recently got this korg that needs help. It would not get any power. After opening it up and testing things, it seemed the transformer is at fault surprisingly. 1st bad transformer Ive ever seen. Got power going to the transformer from the plug/switch, and on the primary side of the transformer... but the secondary side only read 13v..
Now this is where I need some advice or help. After considering the options of replacing the transformer I ended up uncertain about some things.

The transformer has printed on it "100v 19.9v 35.8va"
Looking at the boards schematics in the manual, that line says 25v, and not 19.9v... |:

At first I blamed the regional difference for what is printed on the transformer, but the more I thought about it, the more puzzling it got. I wondered if a mis-specification is why the transformer is bad to begin with. I know some electronics get sent out that way...

My main question is, would the specification of transformer make a difference?
Say if I used a typical transformer with 40va and 120v/24v? Could that effect the performance of the dw8000?
Also could it effect/hurt other components down the line?

Or would the board just take what it needed off the 24v?

Im curious to know what someone else is getting on their secondary side, so if anybody else on here happens to have tackled this problem and knows, or has their dw8000 open? :D

Any advice is seriously appreciated.
Thank you!
Last edited by Algorithm on Sun Mar 16, 2014 6:10 am, edited 1 time in total.
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Re: Korg DW8000 issues

Postby rhino » Mon Feb 24, 2014 9:51 pm

Welcome to the board!

SYNTAUR.com has a used xfromer here:
http://www.syntaur.com/4388.html

Are you testing the transformer with it connected to the power supply?
Are you measuring the secondary with the AC SCALE?

If the synth is "dead" - that is NOTHING...no display, lights on the buttons, any noise, smoke etc.
check the +5 volt output of the power supply board.
Thoughts:
bad rectifier(s)
bad regulator(s)
short filter cap (likely visible)

My schematic shows the transformer has a 117-volt tap. You should be able to just change one wire.

Was the synth d.o.a.? If so, look for a botched battery change job with globs of solder shorting something.

Let us know.
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Re: Korg DW8000 issues

Postby Algorithm » Mon Feb 24, 2014 10:18 pm

Thank you greatly! (:


No, it was tested disconnected from the power supply board.
Yes, the meter was on AC.

Yeah, it would be in the "dead" genre, temporarily.
I received it this way, so I cant say what occurred when things went bad.

Well, that is the thing, inside, it says 100v 19.9v 35.8va on the transformer, on the stamp on the outside back? It says 117v.

I already changed the wires on the taps to see if any other line let power to the other side, but no dice.

Yeah, bought it broken, but battery looks original, definitely needs to be replaced.
I definitely have to change a few caps as well. I want to see it getting power before that though.

So it is important to use the custom transformer made particularly for these korgs?


Thanks again. (:
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Re: Korg DW8000 issues

Postby rhino » Mon Feb 24, 2014 11:12 pm

Well.....
Do you get the same voltage on each side of the center-tap? Does the xformer overheat? Buzz or hum?

Let me open one of mine and check some other things.

Sorry for the "dumb" questions last post. There are a lot of synth owners who are clueless about electronics inside.

Never seen a bad xformer either...but vintage IS vintage!!!! (lol)

Where in Ky are you? I'm in Richmond - 20 mi. south of Lexington.
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Re: Korg DW8000 issues

Postby Algorithm » Mon Feb 24, 2014 11:32 pm

13v on bottom, nothing on top.

No sound or hum, the plastic looking (originally white?) is quite brown, but I have seen other transformers going looking similarly. Its not black or anything, no bulges either. This is really 1 of my first times delving into such old equipment though, the majority of this stuff is older than me! haha. Its hard for me to say about overheating.

That would be great! Thank you.

No need to apologize, everything you suggested was good advice! (:

Im far western KY, nearly to Illinois, in a middle of nowhere sort of place.
When I read Hills of Kentucky I pictured the mountains of Lexington ((;
Beautiful place. :D
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Re: Korg DW8000 issues

Postby rhino » Tue Feb 25, 2014 12:46 am

power on one side of the centertap and not on the other points to a bad xformer. 99%.
The spects you posted would seem to work. Just watch that the replacement is not too tall to fit in the cabinet.

I've dealt with Syntaur many, many time over the last 10 years and always had a good transaction.
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Re: Korg DW8000 issues

Postby Algorithm » Tue Feb 25, 2014 1:03 am

Perfect.

I already ordered one from syntaur, so no worries there.
Thank you for the information also, good to know in case an exact replacement isnt available.

Man, that sounds like a lovely view.
Its seriously unreally beautiful around there.
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Re: Korg DW8000 issues

Postby Algorithm » Sat Mar 15, 2014 9:39 pm

Made a litte bit of progress.
I changed the transformer.
I changed the caps, didnt fix it.
I changed the bridge rectifier, tested the psu headers, was missing +5v on 2 of the 3 headers.
This morning retested things, they all checked out... :|

and now I get power on.
But the sound it outputs is all wrong.

I changed the battery because it was only half full.
Reloaded the tape.

It didnt fix the wrong aspect of the sound.
Nearly all the notes are the same.
Half the time being lower on the higher side.

(I dont have an oscilloscope)

Any advice is appreciated.
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Re: Korg DW8000 issues

Postby rhino » Sun Mar 16, 2014 12:34 am

Try this:
With power OFF, hold down buttons 5 and 8 while powering ON.
Then re-load the tape.

When the battery is removed, the DW8000 RAM can get corrupted and not load from the tape correctly.
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Re: Korg DW8000 issues

Postby Algorithm » Sun Mar 16, 2014 2:49 am

Thank you again Rhino.
I erased all the patches, reloaded them from tape, got 60 0D and still, half the notes sounded the same, but different in pitch or tuning? sounded insane..

Its strange, I got varying readings at different points, I would test part of it, it would look good, the next day it wasnt checking out.

After the patchwipe and still sounded ultra gritty?
Took it apart, checked again, I lost the lowest +5v on the 6 pin header. After it was there before I bolted it up. :?
Traced that back to IC2, which was bad. 7805, luckily radioshack in my town had those.
(It gets so old having to wait for parts in the mail)
Hopefully this will fix it. I will add some more to this thread soon.

I noticed the bottom traces on the green boards in the dw8000 are beautiful. 8-)
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Re: Korg DW8000 issues

Postby Algorithm » Sun Mar 16, 2014 6:10 am

Replaced 7805 and all is right! :D
Another 1 rescued from the trash heap!
Had a lot of fun playing it, the editing system is super simple, the arpeggiator is nice as well.
Sounds great.
Thanks again Rhino!
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Re: Korg DW8000 issues

Postby HideawayStudio » Sun Mar 16, 2014 10:16 pm

Algorithm wrote:Replaced 7805 and all is right! :D
Another 1 rescued from the trash heap!
Had a lot of fun playing it, the editing system is super simple, the arpeggiator is nice as well.
Sounds great.
Thanks again Rhino!


Curious - the same regulator failed in my DW-8000 a couple of years ago. Maybe it's a bit of a weakness in these synths.
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Re: Korg DW8000 issues

Postby rhino » Mon Mar 17, 2014 3:25 am

Some early integrated voltage regulators had QC problems... like the ones on the Fizmo. Heat buildup did them in.
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Re: Korg DW8000 issues

Postby sammy123 » Mon Mar 17, 2014 10:06 pm

Congratulations getting you board up and running. As a fellow DW owner it is great to read stuff like this.
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Re: Korg DW8000 issues

Postby Algorithm » Tue Mar 18, 2014 1:13 am

Thanks. Yeah, I am looking back on that fix fondly as I wait for the glue to dry on the panel board for this d-50...
Going to have to jump the crack with wires on about 20 traces . ((:
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