Korg Poly800/EX800 Users

I suspect your -5V circuit has an open diode or transistor based on your description.

IC1 needs a -5V supply along with a +5V supply.  It can partially function with +5V by giving you high volume.. but will fall on it's face when you try to control volume reduction.. sound familiar?
Your joystick not working also makes me suspect the -5V supply.. it also requires -5V to function.

Take a look at block "16" on the schematic.  It is at the bottom left corner, right below "Memory Backup".
I suspect one of the diodes or transistors in there is shorted open.. most likely damaged when the event that damaged Q1 happened.


-Blaine



--- In korgpolyex@yahoogroups.com, Tavish McDonald <tavishmcronald@...> wrote:
>
> Hi, this solved the noise problem, thank you! Now the problems have been
> narrowed down. I seem to be able to control a majority of the dco
> functions. The joystick doesn't work, and editing vcf doesn't do much, I
> think at times I can hear it slightly changing. When I play with the vcf
> trim pots they function. DEGs don't seem to do much, they do function to an
> extent. I've played around with them while having the sequencer on and I
> seem to get a gated effect most of the time, it's hard to explain but it
> sounds like there is no smooth release. When I play keys I will play a note
> it will play the note with that kinda gated effect on it when it ends (and
> I cannot get a slow attack), then I play another note and the last note I
> played will trigger with it. It's hard for me to explain but hopefully that
> helps. Anyways, it has a nice sound to it now that the noise is gone it
> just isn't playable/editable
> 
> On Thu, Sep 20, 2012 at 9:08 AM, bimmerfan222 <bperkins211@...> wrote:
> 
> > **
> >
> >
> >
> >
> > Since I was dabbling around the VCF/VCA chip's diagram (IC 1/NJM2069)...
> > comparing it to a CEM 3372 and other CEM VCF/VCA's, it dawned on me that
> > you may have a problem with either the Noise Generator circuit itself, IC
> > 1, or a bad signal going into IC 1 at pin 9 (the CPU's Noise Level Control).
> >
> > Here's where to look at the schematics:
> >
> > If you look at the schematic for the main board, you will see sections of
> > the schematic blocked around. The area of interest right now is at the
> > lower right, near IC 1. It is block section #29 (29 is circled).
> > That's the Noise Generator circuit. You will notice there is a variable
> > resistor inside that block. VR3.
> > You might try turning that VR all the way down and see if it reduces your
> > noise level.. that VR should be the first stage of NOISE level... it's
> > independent of CPU control.
> > If you follow the circuit, you will see that section's final ouput from
> > the IC2 (m5223 Dual OpAmp) goes into PIN 7 of the IC 1 chip. This is IC1's
> > "VCF SIG in", or source of HISS you get (the hiss is generated by
> > transistor Q5). It is IC1's 3rd VCA signal input.. the other two VCA signal
> > inputs are at PINs 20&21.. they are for DCO1 and DCO2.
> > PIN 9 is how the CPU controls the Noise Level (your parameter settings,
> > etc.), I believe it is a CV input and is affected like this, "voltages at
> > this pin are 0v = 0% volume, 3.83 volts = 50% volume,
> > and 7.65 volts = 100% volume."
> > So it may be possible to check the voltage level at Pin 9. and see if you
> > have a high voltage level there when your parameter setting for NOISE is at
> > 0. If you're parameter NOISE level is 0, that pin should be 0V or very
> > close to it.
> > If it's say, 2-8V.. then something has gone wrong further back in the
> > control line.
> > Just my WAG.
> >
> > If you want a cleaner schematic to look at, check this link for a MII
> > Service Manual.
> >
> > http://www.synfo.nl/servicemanuals/Korg/POLY-800II_SERVICE_MANUAL.pdf
> >
> > BEWARE tho... things are different from a M1 to a M2. But I like to keep a
> > copy of a M2 pdf handy for areas I have difficulty reading on the M1 pdf
> > since most of the core circuitry is the same.. such as the Noise generator
> > circuit section and most of the main board.. minus the alterations done to
> > slip in the expansion board for a M2 to have Digital Delay.
> > There are also a few errors in the M2 schematic that I wont go into right
> > now.. the point is that you can use that pdf to get a clearer view of an
> > area that is smudged up on the M1 pdf.. for the most part.
> >
> > Here is a link to a discussion about the IC1/NJM2069.
> >
> > http://sounddoctorin.com/synthtec/korg/njm2069.htm
> >
> > They are discussing the use of IC1 in a different Korg. The DSS-1. Korg's
> > first Digital Sampler.
> > The application in the DSS-1 is a bit different than a Poly 800, but I
> > figured it was handy info to have.
> > The diagram you want to stick to of IC1 is on page 30 (pdf page#, not
> > manual page) of the M1 pdf.
> >
> > IC1/NJM2069 is a very difficult IC to find for sale on ebay, etc. It was
> > Korg's very own chip (perhaps their own version of a CEM chip). So if it's
> > gone bad on you, there's not much that can be done unless you get it from
> > another Korg synth that has one in it.
> > But.. there might be a possibility to retrofit a CEM VCF/VCA into the
> > Korg. Yea.. some may laugh or snear or perhaps even cry BLASPHEMY! at me
> > for even thinking of doing this to a Poly 800.. but CEM chips are a damn
> > good sounding chip. They are in SC Prophet 5's, Oberheim's and a slew of
> > other classic sounding synths.
> >
> > Here's a link to a CEM 3372 datasheet. You'll see how somewhat similar it
> > is to Korg's NJM2069
> >
> > http://www.synthtech.com/cem/c3372pdf.pdf
> >
> > Anyway.. I'm getting off the subject here.
> > Give a go at VR3 and see if turning it DOWN will help reduce your noise
> > level. If it does (and it should). then we can try to move on to other
> > areas to look for problems.. which is probably the input CONTROL signal at
> > PIN9 of the IC1 chip.
> >
> > Maybe Mike can chime in here a bit on this too.. I've had to be corrected
> > by him several times before and sure to be again, LOL.
> > This HISS problem is a recurring issue with this synth. Maybe if we
> > collaborate on understanding the synth's circuitry, we can help others with
> > problems like yours in the future.
> > I got a feeling your problem is an issue that is related to your Q1 having
> > been removed. Usually Q1 goes bad because someone shorted it out.. and if
> > Q1 gets shorted.. it could have botched up another component that controls
> > the Noise Level.
> >
> > HTH's
> >
> > -Blaine
> >
> > --- In korgpolyex@yahoogroups.com, "mcdonaldtavish" <tavishmcronald@>
> > wrote:
> > >
> > > Hi, just made a trade for a broken poly 800. At first glance this is
> > what I have noticed about my broken unit. Let me start by saying I have yet
> > to open this thing up. I tried to reload presets and this had no effect on
> > the board or its problems, I did it multiple times, it said "good" then I
> > switched back to tape disable and it sounded the same, nothing changed at
> > all. Unit powers on and seems to respond to parameter changes to an extent,
> > for instance I can change deg1 attack value, and the display shows the
> > parameter number I chose and the value I'm changing. it kinda effects the
> > sound but it is clear that the sound is not right in the first place (it is
> > like that with most of the parameters except the noise, dco levels and vcf
> > functions don't seem to do much of anything), so some of the parameters
> > seem to half work, I can hear them change but the overall sound just isn't
> > right at all and has a loud hiss to it. In the background you can hear the
> > sound playing but over that is the hiss. it's as if the noise generator is
> > at full blast, the dcos are turned down (it doesn't sound like a ground
> > hum) and the filter is open and at hi resonance. I can usually tell when
> > chorus is on or off, the tune fader seems to work. The bend joystick
> > doesn't seem to do anything. The headphone jack doesn't work. When it first
> > powers on it wont make any sound, after about 30 seconds to a minute it
> > starts to make a sound that starts with the filter cutoff low but slowly
> > rising, I can take my finger off the key and it will stop, when I press
> > back on the key it starts from where it left off on the filter cutoff
> > envelope and eventually fully rises and stays that way. The sequencer seems
> > to work, it just plays the messed up noise, I can change speed and I think
> > I missed around the with steps. When the sequencer is on the display
> > flashes, the flashes speed up when the sequence speeds up. All the keys
> > function and you can hear the pitch of each key you press, but here's the
> > weird part, you press a note and then you take your finger off and the note
> > stops, then you play another key and it plays both notes together and so
> > on. It's hard for me to explain most of this in a coherent way so my
> > apologies, but hopefully you guys are getting a feel for the issues I'm
> > having with my poly 800. Any suggestions would be great appreciated, I have
> > a lot of solder experience but I don't know how to troubleshoot circuits or
> > anything like that.
> > >
> > > Thanks guys.
> > >
> >
> >  
> >
>