I haven't actually tested the LED displays themselves, but since the
display driver chips (IC30 and 31) are not outputting anything to the
LED's int he display it seems the issue is there (or probably
somewhere earlier in the cycle).
I think I am about cave and pick up an oscilloscope for this project
(and others!). Any recommendations on a good cheap scope for synth
projects to look for used?
<<aaRoN>>
--- In korgpolyex@yahoogroups.com, LARRY HAWKE <gorgarh@...> wrote:
>
>
> Do you think there's the 'slightest' possibility the display itself
might be dead?
>
> To: korgpolyex@yahoogroups.com
> From: aah_public@...
> Date: Wed, 25 Feb 2009 15:57:05 +0000
> 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@yahoogroups.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@yahoogroups.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.
>
> > >
>
> >
>