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 > > > > > > > > > > > > > > >
Message
Re: Dead 800
2009-03-07 by selloutdesigns