Definitely timing issues with IC36b the interrupt oscillator. Try disconnecting the output at R107 and see if it runs at the correct frequency. If it does the CPU is loading it down somehow. If not then suspect the timing caps C76 or C79. The resistors R102-R104 need to be verified and then the Tl072 op amp itself. This circuit needs to run in the mhz or no go for the LED display and envelope generators.
--- In korgpolyex@yahoogroups.com, "selloutdesigns" <aah_public@...> wrote:
>
> I just got my scope and hooked it up last night. The first odd thing I noticed was that CPU RES 7.5 (interrupt oscillator that drives the display and EG/MG among other things) was running at about .34ms per cycle, which is about a 1000 times slower than what it should be (.34usec). Because of the exact 1000x multiplier, I thought maybe I was misreading the scope, but I do not believe I am. For example, when I measure the CPU Clock Out it measures at .3 usec per cycle, but as soon as I switch the probe to CPU RES 7.5 I have to crank up the Time/Div setting. All components check out in that part of the circuit and everything is connected and powered as it should. Any insight as to what might cause this? It does seem if this oscillator is running slow that might be the cause of my display issue.
>
> Other oddities which may be related: CPU ALE seems to be slower than normal, at about 1.375usec per cycle vs. .18usec where it is supposed to be. IO/M is always low. On M81C55, Timer Out is always high.
>
> Thanks is advance for any guidance anyone may have!
>
> <<aaRoN>>
>
> --- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@> wrote:
> >
> > If you have goop from what might have been a battery leak then things can look OK but turn out to be alot worse than you think.
> >
> > Nevertheless, you might be OK. A scope is going to help alot.
> >
> > For example, IO/M signal will spend most of it's time low because it is only high for IO. In the Poly, all of the hardware is mapped into normal memory except for the 81C55. So the IO/M signal is almost 100% low. But a scope will show you thos tiny little 20uS high periods. That would tell you that the CPU was actually doing something as opposed to completely comatose.
> >
> > Mike.
> >
> >
> >
> >
> >
> >
> > ________________________________
> > From: selloutdesigns <aah_public@>
> > To: korgpolyex@yahoogroups.com
> > Sent: Wednesday, February 25, 2009 10:57:05 AM
> > Subject: [korgpolyex] Re: Dead 800
> >
> >
> > Took another look internally last night. There was some sticky gunk on
> > some of the boards which may have been from a battery compartment leak
> > at some point, but it cleaned up fine and there appears to be no trace
> > or component damage. As best I can tell, all the rails are showing
> > correct voltages. Strangely I found that the rails on the main board
> > differed slightly from the smaller board (KLM-598), being about 4.6V.
> > However, adjusting VR1 slightly boosted this voltage to 5V, while
> > causing voltage rails on the main board to be slightly above 5V. I am
> > guessing this is all within tolerable range though.
> >
> > I also took voltage measurements on all the pins on IC24 (M80C85A) and
> > IC25 (M81C55). I see a voltage on all the output pins of IC24
> > connecting to the input pins of IC25. However, the output pins of IC25
> > (which feed the display driver circuit) all show 0V. IC24 and 25 both
> > are powered. I did notice that IO/M (both), RESOUT (IC24) and RES
> > (IC25) were showing 0V. Is it correct to assume that if IO/M is always
> > low, that IC25 will never output any data? What would be keeping IC24
> > from toggling IO/M to high?
> >
> > Thanks in advance for any insight/guidance. Anyone have scans of a
> > Poly 800 Service Manual they can share? :)
> >
> > --- In korgpolyex@yahoogro ups.com, Michael Hawkins <korgpolyex800@ ...>
> > wrote:
> > >
> > > Aaron,
> > >
> > > you should check all voltage rails. especially +5 and -5 volt rails.
> > >
> > > The power supply of the Poly is somewhat reliable. Note the "somewhat".
> > >
> > > Sometimes it does fail or drift enough to cause Poly's to die.
> > >
> > > If you don't have a display showing then tape and patches etc are 99
> > percent NOT going to work.
> > >
> > > Even when memory is corrupted due to battery failure, those
> > display's will at least show something.
> > >
> > > Also, I would give the thing a complete internal thorough check out
> > looking for battery acid damage, broken wires, misaligned or misplaced
> > connectors etc.
> > >
> > > Sometimes it's the simple things.
> > >
> > > Mike.
> > >
> > >
> > >
> > >
> > >
> > > ____________ _________ _________ __
> > > From: selloutdesigns <aah_public@ ...>
> > > To: korgpolyex@yahoogro ups.com
> > > Sent: Tuesday, February 24, 2009 9:48:45 AM
> > > Subject: [korgpolyex] Re: Dead 800
> > >
> > >
> > > I gave this a try on my dead Poly, but no luck. It seems that VR1
> > > adjusts the +5V rail voltage and subsequently the supply voltage to
> > > the CPU, but in my case it seems like all the chips are getting
> > > adequate power.
> > >
> > > <<aaRoN>>
> > > --- In korgpolyex@yahoogro ups.com, Russ <russdaren@ ..> wrote:
> > > >
> > > > I had this problem a while ago and got her back upby fiddling with
> > > one of the VR pots. Cant recal which one did it. But one of them
> > > seemed to control voltage for the CPU board. It wnet from no display,
> > > to garbled, to functioning just fine ever since.
> > > >
> > >
> >
>