going to check now if IC38 (tl062) has input on pin 5 coming from the output of the BR..!
As i can understand from the schematic theres no actual DAC (i said that before too i think xD ) and the output voltage comes from dividing the voltage from 8 pins of the 81c55 where some of them come throught the IC32 (4050)..!
I ll report back later..!
--- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@...> wrote:
>
> I will check ic 12 if anything happens in the input pin of the chip when i change a value...Well as i saw from the service manual there is no
> native (IC) DAC for these features at all..!
> Everything goes with a block resistor and a 4050 ic for level normalising..Is it true or i have misunderstood what i saw?
>
> Yes, that pretty much sums up the D2A and sample and hold section for the controls that are dead.
>
> As the service manual says for section 12 (see schematic):
>
> 12) 8-bit D/A converter:
> Uses CMOS noninverting buffer IC32 (HD14050 or �4050�), and 8R9 (RKM10L253F or �BR9�) a 10-pin (Rm25kohm) R-2R ladder resistor in D/A converter with output of 0V~4V.
>
> So I would look for the output of the D2A first, then check after the buffer then check the 4050 then the sample and hold buffers.
>
>
> So your oscilloscope should be able to see if the D2A is the problem or the multiplexer 4050 or the sample and hold buffers are the problem or something else. And you can also trace the levels for all of the various control signals that go out from the sample and hold buffers to control the VCF, DCO MG, volume etc.
>
> Mike
>
>
> ________________________________
> From: iamakisgr <iamakisgr@...>
> To: korgpolyex@yahoogroups.com
> Sent: Wednesday, December 28, 2011 7:34 PM
> Subject: [korgpolyex] Re: Problem with my poly800 reverse keys edition... :/
>
>
> Â
> Well all envelopes work, also chorus works ,the controlls of the filter chip dont work at all i think...
> I have an oscilloscope but it doesnt have component tester...
> Its an hameg hm-203 (no numbers after it, its the first model) dual channel 20mhz..
> I will check ic 12 if anything happens in the input pin of the chip when i change a value...Well as i saw from the service manual there is no native (IC) DAC for these features at all..!
> Everything goes with a block resistor and a 4050 ic for level normalising..Is it true or i have misunderstood what i saw?
>
> --- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@> wrote:
> >
> > I think it is quite safe to say that the microprocessor, memory and ROM and decoding logic are all OK because you have the ability to change parameters. If you did not get "11 P" when you power up then that might mean you have a problem with the CPU but since you do see that and you can change parameters, it would appear that all of the CPU side of things is OK.
> >
> > Also, the display is driven by the 81C55 IO chip, so the fact that you see the display and that you can change parameters means that the 81C55 is OK too.
> >
> > The multiplexer is IC12 which is a HD14051. You can use a standard CMOS 4051 to replace it.
> >
> > Do you have an oscilloscope? It will be easier and much faster to determine where the exact fault is if you have one.
> >
> >
> > Mike
> >
> >
> > ________________________________
> > From: iamakisgr <iamakisgr@>
> > To: korgpolyex@yahoogroups.com
> > Sent: Tuesday, December 27, 2011 5:30 PM
> > Subject: [korgpolyex] Re: Problem with my poly800 reverse keys edition... :/
> >
> >
> > Ã�Â
> > Hello!
> > Thanks for the reply..!
> > None of these work at all..
> > All other functions work though..!
> > Can you please tell me the ic number that makes the d/a convertion for those features?
> > Also,can it be the microcontroler pin outputs the problem?
> > Akis
> > --- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@> wrote:
> > >
> > > It sounds to me like you should be looking for problems with the digital to analog converter and then perhaps the multiplexer that drives the analog signal out to the various controls for the DCO MG, VCF MG and the master volume control.
> > >
> > > Check the following and let us know which ones work and which ones don't work:
> > >
> > > 1) parameter 17 - DCO 1 volume control
> > > 2) parameter 27 - DCO 2 volume control
> > > 3) parameter 33 - noise level
> > > 4) parameter 41 - VCF cut off
> > > 5) parameter 42 - resonance
> > > 6) parameter 83 - DCO modulation
> > >
> > > 7) parameter 84 - VCF modulation
> > > 8) joystick bend
> > >
> > > If NONE of these work then the D2A converter, the sample and hold and the multiplexer sections need to be checked.
> > >
> > > If some of them work then the D2A converter is probably OK but the sample and hold and multiplexer sections need to be checked.
> > >
> > > Mike
> > >
> > >
> > >
> > > ________________________________
> > > From: iamakisgr <iamakisgr@>
> > > To: korgpolyex@yahoogroups.com
> > > Sent: Monday, December 26, 2011 5:20 PM
> > > Subject: [korgpolyex] Re: Problem with my poly800 reverse keys edition... :/
> > >
> > >
> > > Ã��Ã�Â
> > > There are many functions that dont work..
> > > first of all the filter...
> > > The chip works cause i tested it with a pot and 3 volt directly and it responds ok...
> > > I couldnt find the problem going back to beggining of the signal..
> > > Maybe i dont know enough to fix it or i cant consentrate,thats why i am asking what to check first...
> > > Thanks everyone for trying to help me.
> > > If theres anything i can make to help you understand whats the problem and what i have done so far in testing and checking please tell me and i will try to explain the best way i can..
> > >
> > > --- In korgpolyex@yahoogroups.com, Gordon JC Pearce <gordon@> wrote:
> > > >
> > > > On Mon, 26 Dec 2011 15:25:20 -0000
> > > > "iamakisgr" <iamakisgr@> wrote:
> > > >
> > > > > Well..I have tried all that..
> > > > > I even connected +/- 5volts from a pc psu at the points that the service manual said i should check and have 5 volts...
> > > > > I have sound to the output but the filter dont work at all nor the eg, nor the lfo...
> > > > > I just hear the wave with no cutoff (too bright) and no resonanse..
> > > > > I tried alternating them from the menu but nothing happened.. :/
> > > > > Any other suggestions?
> > > > > What should i look for before changing everything on the motherboard except the eeprom, the sound chip and the filter chip which i have tested and they work?
> > > >
> > > > You need to stop all this poke and hope stuff, and start trying to diagnose the problem.
> > > >
> > > > First off, what works? What doesn't work? If for example you have the oscillator outputs working but no filtering then perhaps you should start looking at how the filter CV is generated.
> > > >
> > > > --
> > > > Gordon JC Pearce MM0YEQ <gordonjcp@>
> > > >
> > >
> >
>