Discussion about the Korg PolySix synthesizer

Hi Malte,

@aj: I feel we are making some progress here (at last)...
> 
> your observations go along with my theory that this is a question of the
> balance of the clock signals. By attaching the probe to C22 (or XTAL1 at
> the chip) you increase the capacitance of C22 (which should originally be
> 10pF, not 22pF).
> On the other hand I had decreased the capacitance of C23 (originally 22pF,
> now 10pF but I first tested this with a 22pF and 10pF cap in series which
> should give less than 7pF).
> 
> @aj: So just to recap you new have both C22 and C23 at 10pF and all is stable?
> 
> As I said earlier my measurements probably don't amount to much. I again
> measured with the 10x probe setting. So even if we ignore the actual values
> the following was still apearent:
> 
> - the signals on XTAL1 and XTAL2 are closer in amplitude on the old boards
> than on the new boards
> - exchanging C23 for a smaller value brought up the amplitude for XTAL2 on
> the new board
> 
> All this was only measurable with the 10x probe setting; the measurements
> with the 1x setting did not show such a strong difference (but they almost
> always locked up the processor and showed a completely different waveform).
> If I'm reading this right my probe has a capacitance of around 100pF in the
> 1x range and around 15pF in the 10x range - which of course explains why
> measuring with the 1x setting does no good.
> 
> @aj: I have the same issue. If I go anywhere near XTAL2 with my test gear the
> CPU halts/crashes. This is also the case on the original Œ367. Even with the
> probes in x10 mode. That aside the amplitude of the clock signal is
> significantly lower on the XTAL2 side.
> 
> The new board with the different C23 value has been running now for over 12
> hours.
> 
> @aj: I am going to try your suggested values with this board and then run
> through my routines to and see if I can get it to behave in an erratic way.
> 
> I need to find out how to make screenshots from my scope (it's a digital
> one); or perhaps I'll simply take pictures with the camera.
>  
> @aj: My scope is so old it has an interface for an RS-232 line printer! I
> think in this case a photo might be best!
> 
> Cheers,
> Andy   



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