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Re: Korg DW8000 not working, please help.

Posted: Sat Sep 02, 2017 9:29 pm
by Riinehart
Cool, I hope it works out. One other thing I wanted to share with you that I found interesting. Again, it's specific to the mod, but might be the same with any of the ICs.

The little mini-board for the mod plugs into the IC38 socket ... and what kept happening was that I'd pull it out, re-seat it, everything would be fine, and then I'd close the lid and as soon as there was a little pressure on it, the screen would black out again.

The piece of this that might be useful to you is that, simply straightening it out would NOT reset it -- it would only reset if I turned off the synth, removed the chip from the socket, put it back in, and then turned it back on again.No idea if it would work for you, but if all the connections look good, maybe pull the EPROM chip and put it back in? At least it would be quick and easy to try (just be careful with the pins, of course).

Re: Korg DW8000 not working, please help.

Posted: Sat Sep 02, 2017 11:30 pm
by Mooger5
JHatzia wrote:I bought this unit in this state. It had a battery replacement with a holder, I decided to redo it with an additional diode installed in-between the + terminal of the holder and on the board.
There are two diodes in the battery circuit, but neither one is directly connected to the plus terminal of the holder.
I´m going to post a detailed picture in a few moments.

Re: Korg DW8000 not working, please help.

Posted: Sat Sep 02, 2017 11:54 pm
by Mooger5
Here... Point A is the +5V rail that feeds all the logic. You´ll find point A all over the schematic, as it´s the same voltage coming from the +5V regulator in the PSU. There should be continuity between them all.
That one in particular feeds the memory IC36 when the power in ON. Notice the current goes through diode D7 to pin 24.
The battery also feeds IC36 through a diode, D6, but there´s R53 between the diode and the plus terminal.
What are the roles of the diodes? Well, D6 is there to prevent current coming from point A to charge the battery when the power is on. D7 is there to prevent the battery from feeding a current to other logic chips powered by the +5V rail when the power is off. When the synth shuts down there´s only the memory IC37 that needs to be continuously powered. Without D7 the battery would quickly discharge.

So if I read that correctly, you added a third diode to the board?

Image

Re: Korg DW8000 not working, please help.

Posted: Sun Sep 03, 2017 12:27 am
by Mooger5
Riinehart wrote:
The little mini-board for the mod plugs into the IC38 socket ... and what kept happening was that I'd pull it out, re-seat it, everything would be fine, and then I'd close the lid and as soon as there was a little pressure on it, the screen would black out again.
Probably when closing the lid there is something inside that presses the mini-board, forcing the mod EPROM to go out of the socket. If there´s no more clearance above the mini-board, you could try using some non conductive spacers or standoffs between the main PCB and the mod.
The piece of this that might be useful to you is that, simply straightening it out would NOT reset it -- it would only reset if I turned off the synth, removed the chip from the socket, put it back in, and then turned it back on again.
I think just turning the synth on after straightening the mini-board is all there is to it, the synth will reset and aknowledge the mod. No need to remove it and put it back on. Besides, doing that, repeatedly trying to fix it, which is understandable, puts the only mechanical connection under stress.

So what looked like a severe electronic failure turned out to be a mechanical problem. Looks like you´re close to fixing it.

Re: Korg DW8000 not working, please help.

Posted: Sun Sep 03, 2017 3:49 am
by Riinehart
Mooger5, funny you mention it, that's exactly what I did. I created little standoffs so that the rest of the board can't move when the lid closes. Seems to be holding up so far.

Thanks again for the thought and help. And Jhatzia, wishing you luck!

Re: Korg DW8000 not working, please help.

Posted: Thu Sep 07, 2017 6:44 am
by JHatzia
After reading through this thread again, I redid the battery job, dropped the added diode to the + terminal. Tested IC36, all of that area is getting 3V just fine. I also resoldered all of the connectors and examined the board closely for cracked solder joints. I also ended up cleaning the board but, still, am in the same situation. The joystick is the only thing that makes the synth react beside it's locked up state. It behaves almost as if it's not connected properly. I double checked the cables, and they all appear correct, just like when I first received this unit, so it's still a mystery.. I'll check all the 5v rails in the meantime.

Re: Korg DW8000 not working, please help.

Posted: Thu Sep 07, 2017 1:50 pm
by Mooger5
If every voltage point checks out, you may have to start searching for a new CPU. The block diagram and the video you posted seem to suggest this. With the service manual and the datasheet for IC35 at hand, checking the pulse trains with a logic probe at the input and output ports should confirm it. Or rule it out, you will never know unless you run that test, I think.

Re: Korg DW8000 not working, please help.

Posted: Thu Sep 07, 2017 9:08 pm
by JHatzia
Thank you for the suggestion. Thankfully I do have a logic probe but have yet to have an opportunity to use it. I will try and follow the diagram to see if the CPU is at fault.

Re: Korg DW8000 not working, please help.

Posted: Tue Apr 30, 2019 2:23 am
by ioth_
hey there, I just created an account to let you know how I fixed this exact problem that riinehart (and maybe jhatzia) had.
I bought a filthi dw8000 very cheap, at first it worked, but half of the keys didnt respond. so i played it a while with the keys that were working, then started to experirience dropouts, meaning the machine was "rebooting" (showing 8000 on the display) in intervals that were getting shorter. then It didnt turn on, onl the arp light lit, after a while being in that state I got the display with the 5 single lines, the same as in the image that was posted. Then after another little while I got the weird erratic flashes of random charakters.
Also holding down buttons to get firmware, clear memory, etc. werent working.
Then i opened it up and gave it a good clean, as i said it was filthy. checked the battery and saw it was already changed once, so I measured it and got a good 3v with seems normal I guess?
also cleaned the keyboard contacts and the buttons/sliders while I was at it.
After that for the first evening, I still had the same errors. then the next day, it somehow turned on, but very weird. when i pressed a key, weird oscillating lfo-ish sounds played, but i could only change parameters starting with an 8 (so midi and arp setting, and even those gave off weird values, no numbers, just strange charakters.)
then i tried midi dumping some presets i found only, but that didnt work.
What fixed it however, i activated the tape input, and sent it some correct presets via the tape in.
I switched it off and on again, and there, it was working like a charm. :)
I guess it was just too many out of range values in the ram or whatever.
So i recommend if you start experiencing these errors, try dumping some valid presets on it.

Re: Korg DW8000 not working, please help.

Posted: Tue Apr 30, 2019 9:01 am
by Mooger5
That's it! Your guessing of the memory filled with wild values makes absolute sense. Pretty much the symptoms described involve storable parameters. And they somehow interfere with some system functions.The only way to decorrupt the ram also explains why korg insists on loading the correct presets via tape in the contemporary poly800. This always got me puzzled and was afraid of the day my dw8000 would start misbehaving. Wow perfect troubleshooting and thanks for sharing.
Regards.

Re: Korg DW8000 not working, please help.

Posted: Thu May 02, 2019 2:16 pm
by ioth_
No problem, thanks :)
I guess the tape in is more stable and "direct" than the midi in via sysex, wich could explain why this still worked when the midi dump didnt.

Re: Korg DW8000 not working, please help.

Posted: Thu May 02, 2019 2:34 pm
by ioth_
oh and does anyone know of a place in europe where i can source a value slider for a dw8000?
Only found syntaur, but theyre in the us.

Re: Korg DW8000 not working, please help.

Posted: Thu May 02, 2019 9:28 pm
by Mooger5
The keywords are: slide potentiometer mono 100k linear 30mm travel
I found this from Mouser (EU):
https://eu.mouser.com/ProductDetail/Alp ... tACofac%3D
They also sell with an LED in place of the cap.
From Banzai Music, with a different wiper:
https://www.banzaimusic.com/Alpha-Slide ... K-lin.html

Note that even Syntaur doesn't provide a 100% identical slider; it has to be trimmed to fit the cap. Always keep the original part. If the wiper/traveller/shaft isn´t broken of course, you can always use it on the new part.

Re: Korg DW8000 not working, please help.

Posted: Wed May 22, 2019 8:32 am
by walter
Hello all, I got this Korg DW-8000 synthesizer this morning and as I was checking its pure waveforms, I found that there is a weird thing happening to the notes. Sounds like a higher octave is interfering with lower notes and I cannot play it as it should. It happens in both the oscillators and only with the first four waveforms, as you can see in the video, after the 4th, all sounds well. Any known solution to this problem? Thanks in advance!

Re: Korg DW8000 not working, please help.

Posted: Sat Apr 04, 2020 3:55 am
by 5-HTP
I'm troubleshooting a DW8000 with exactly the same problems described by HappyFunTimes, JHatzia and Riinehart in this thread: mostly the Speed LED is lit, sometimes other LEDs and a random characters are displayed with flickering, and moving the joystick causes additional fickering and random characters. Similarly, all my voltages at the power supply are within spec (rebuilt many years ago with new caps and regs), and the battery is also showing 3V.

I know this thread has been quiet for a few years, but wondering if any progress has been made in diagnosing this seemingly common problem??