Korg Poly800/EX800 Users

Moe,

I very much doubt the problem will be CPU itself.

Since this last email to you I sent another that told of how I fixed
one of my other Poly 800's that had similar problem to yours.

I found that IC33 had failed on one pin and as a result button 7 was
effectively stuck on. This caused my poly to power up immediately
showing a strange display.

Before I worked out that it was the chip itself, I checked the
keyboards lines, the steering diodes and the DTC's.

Look back for that email because it was quite detailed.

Good luck,

Mike



--- In korgpolyex@yahoogroups.com, "m.sislack" <m.sislack@...> wrote:
>
> Hi mike :)
> 
> I put the project aside for a while. I again made sure, that I had 
> the right voltages in the circuit but since I´m not a so much 
> experienced technician, I could not get any closer to a solution. 
> Maybe I have to consider a malfunction of the cpu at last. I don´t 
> know... a service-manual might be helpful ;/
> 
> moe
> 
> --- In korgpolyex@yahoogroups.com, "korgpolyex800" 
> <korgpolyex800@> wrote:
> >
> > Hi Moe,
> > 
> > How did you go working on your Poly with the weird display problem?
> > Reason I ask is that I pulled out of storage my most beat up Poly 
> 800
> > and discovered that it has a very similar problem.
> > 
> > In my case, when I power up the Poly the display immediately 
> shows "7-
> > P". So it looks like the 7 button is stuck down. Also, if I set the
> > sequencer enable switch on the back then power up the keyboard it 
> also
> > displays "11 50 01".
> > 
> > So I think I have a problem that is very similar to yours. I know 
> that
> > the 7 switch is not stuck because I swapped out the main board into 
> my
> > EX-800 and it still does the same thing.
> > 
> > So over the next week I will be looking closely at that main board.
> > 
> > Does anyone else have any history with the display behaving weird 
> in a
> > similar way?
> > 
> > Mike.
> > 
> > --- In korgpolyex@yahoogroups.com, "m.sislack" <m.sislack@> wrote:
> > >
> > > --- In korgpolyex@yahoogroups.com, "korgpolyex800" 
> <korgpolyex800@> 
> > > wrote:
> > > >
> > > > 1.8 in the left display is not sequencer edit mode, that's for 
> sure.
> > > > 
> > > > If you turn the keyboard you should get 11 P. Then, if you 
> switched to
> > > > sequencer edit mode the display would change to 11 50 01.
> > > > 
> > > > So it seems you have a more serious problem than just stuck 
> switches.
> > > > 
> > > > Does the keyboard make sounds when you hit keys? If yes, do all 
> of the
> > > > keys work, or just some of them? Which ones?
> > > > 
> > > > Mike.
> > > > 
> > > Hello Mike!
> > > 
> > > In deed it seems to be a more serious problem. Ehen switches on, 
> in the 
> > > display is shown "1.8 50 01", but theres no reaction to key-hits 
> or 
> > > pressed buttons, not even to the switches on the back. Only when 
> VR1 is 
> > > turned, the machine awakes and starts to make weird noises like 
> > > uncontrolled key-hits and noise with cut off-modulations. This is 
> why I 
> > > wonder if the problem might be caused by any dead transistors Q1, 
> Q2 or 
> > > maybe Q18.
> > > 
> > > moe
> > >
> >
>