I haven't given up on the Poly, just my own ability to get it working in a timely fashion. Possibly if I spent a lot more time I would eventually stumble upon the fix, but fortunately I have a local resource that does vintage synth repair who is taking a look at it now. I'm hoping to have the diagnosis soon, and hopefully a functioning unit. Then I can get back to the important business of modding!
<<aaRoN>>
--- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@...> wrote:
>
> Well, you might be giving up a little too early don't you think?
>
> Remind me again but didn't you say it looked like it had some battery leak on it?
>
> If that is the case, then I would take a long, hard look at those spots that you think had those leaks on them.
>
> Because that acid can do it's corrosive thing without showing much damage after you clean it up.
>
> There is an EPROM in the EPROM socket right? ;-)
>
> Mike.
>
>
> ________________________________
> From: selloutdesigns <aah_public@...>
> To: korgpolyex@yahoogroups.com
> Sent: Friday, March 6, 2009 9:53:52 AM
> Subject: [korgpolyex] Re: Dead 800
>
>
> Okay, I'm totally stumped at this point. The main issue I see now with the display is that the IO/M pin on the CPU is low 100% of the time, as confirmed with a scope reading. However, I have no idea why. SOD is also low all the time as well, which is probably related. The CPU clock is fine and I see RD,WR,S0,S1 going high and low on a regular basis so it seems memory reads and writes are occurring fine, but no I/O whatsoever. I'm wondering if there is an issue with the CPU receiving instructions from memory, which is causing the I/O cycle to never occur.
>
> In any case, I have just about given up in trying to figure out what's going on. I think this unit is destined to land on someone else's bench. If it does get fixed I'll be sure to find out what the cause was.
>
> Thanks to all for the input.
>
> <<aaRoN>>
>
> --- In korgpolyex@yahoogro ups.com, Michael Hawkins <korgpolyex800@ ...> wrote:
> >
> > The circuit description is correct.
> >
> > Interrupt RES7.5 runs at around 2400 to 3600 hz.
> >
> > It can't run too fast otherwise the CPU won't do anything else except service this hardware interrupt.
> >
> > A rate of 2.94Mhz is only half the full clock rate of the CPU. So at that speed, the CPU would not even get to fetch one instruction before being interrupted.
> >
> > Mike.
> >
> >
> >
> >
> >
> > ____________ _________ _________ __
> > From: selloutdesigns <aah_public@ ...>
> > To: korgpolyex@yahoogro ups.com
> > Sent: Wednesday, March 4, 2009 4:22:11 PM
> > Subject: [korgpolyex] Re: Dead 800
> >
> >
> > Hmm, now I am starting to think I'm chasing my tail. In the schematic (pg 6 in Service Manual) for the main board, it shows CPU RES 7.5 as running at .34usec per cycle, or about 2.94 Mhz, which is what got me thinking I had a problem there. However, in the description of the Interrupt Oscillator circuit in the Service Guide (pg 18) it reads:
> >
> > "This oscillator cycle is used for the EG, MG, LED displays, and S/H time division processing. Oscillator frequency is 24OOHz-360OHz. Interrupt order is by priority. If this circuit fails, EG operation and LED indication may become erratic."
> >
> > I measured the oscillator at about .34msec per cycle, or 2941Hz, which seems normal according to that.
> >
> > So which is correct? The schematic or the circuit description? I'm starting to think the circuit description. I've tested all the components except the TL072, but all seem fine.
> >
> > <<aaRoN>>
> >
> > 6) -Address Decoder:
> >
> > --- In korgpolyex@yahoogro ups.com, "narfman96" <narfman96@ ..> wrote:
> > >
> > > Should work fine. Install a good socket if you want. Then you can use a TL072 when you get one.
> > >
> > > --- In korgpolyex@yahoogro ups.com, "selloutdesigns" <aah_public@ > wrote:
> > > >
> > > > Anyone know offhand if a tl082 can safely replace a tl072? They do appear compatible.
> > > >
> > > > Thanks,
> > > >
> > > > <<aaRoN>>
> > > >
> > > > --- In korgpolyex@yahoogro ups.com, Gordon JC Pearce MM3YEQ <gordon@> wrote:
> > > > >
> > > > > On Wed, 2009-03-04 at 13:34 +0000, narfman96 wrote:
> > > > > > 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.
> > > > >
> > > > > Bah. Just change the TL072 on spec. Horrible things.
> > > > >
> > > > > Gordon
> > > > >
> > > >
> > >
> >
>