1) If you experience that one voice has this problem, and within this
one voice it is both VCOs then it is very likely that the reason
lies in a component or signal which is common to both VCOs. Otherwise
there must be ∗two∗ problems which show similar effect.
2) Please don't rely on anything that anyone did any-when. If there are
components which have been replaced before, this is no guarantee
that they are working now. Maybe this was 5, 8, 10 years ago? Maybe
there is a reason behind why they failed then, which makes them fail
again? Maybe the guy doing the "repair" built in a bug (e.g. short
circuit, ...)?
You can measure the VCO CV e.g. on ICx11/pin5 on a good voice and on the
bad one. Do it in this way that you first play a low note and then a
high one to see the step in the CV. This would be done best with a
storage oscilloscope, which you probably do not have; but if the "step"
is so slow that you can hear it, you should be able to see the
difference on the scope. How does the CV change? Can you see a ramp
(which is to be supposed when you hear kind of a "portamento" on this
one voice)? Or a step? Is it equal going up vs. going down? How is
the situation when you set the trimpots to a similar position as on a
good voice? Does it sound too high? Too low? Is the scale
approximately correct? - Very difficult to debug this via email ...
If you cannot find it, you may start to disconnect "unnecessary"
circuitry and go to the absolut minimum circuit for one VCO (which is
ICx11 and the 4 bipolar transistors plus caps and resistors; up to the
FET). Maybe it's the FETs, but it is very unlikely that both FETs
have a similar problem, only in one voice.
Good luck,
Johannes
gil_we wrote:
> You know what ?... now I relaize I replaced IC8 and ICx11 as well !
>
> Any other idea you can think of ?
>
> What you're saying is that as long as the problem exist on both VCO
> it must be caused by a common part to both VCO ?...
>
> I'll try the ICx11 ... any other idea you can think of ?
>
>
>
>
>
> --- In PolySix@yahoogroups.com, Johannes Hausensteiner <johau@g...>
> wrote:
>
>>If you already replaced Rx39/Cx10 then the only thing in common
>>for both VCOs in one voice is ICx11 (TL072). THe value of Rx39
>>is not very critical unless it is very different to the nominal
>>value of 1k
>>
>> > By IC8 are you refering to ICx08 ? it's a 4558 opamp.
>>No, I mean IC8, which is a 4051. It is common to all voices; it
>>demultiplexes the CV for the VCOs
>>
>>Johannes
>>
>>
>>gil_we wrote:
>>
>>>Thanks !
>>>
>>>The Cx10 and Rx39 have been already replaced to no avail.
>>>
>>>By IC8 are you refering to ICx08 ? it's a 4558 opamp.
>>>
>>>btw, I now see that I had to replace Rx36 with a slightly
>
> different
>
>>>value because even after the machine is warm enough, with the
>>>original value the related VCO still cannot get tuned with the
>
> other
>
>>>oscillators, not matter how you set the VCO tuning trimmers.
>>>
>>>Thanks again.
>>>
>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>
> <johau@g...>
>
>>>wrote:
>>>
>>>
>>>>Hi,
>>>>
>>>>The caps are Cx10 ... where x is the voice number. On the
>
> schematics
>
>>>>only voice #7 is drawn in detail, so you can see C710. Maybe it
>
> is
>
>>>not
>>>
>>>
>>>>the cap but the accompanying resistor (R739), or the demux (IC8).
>>>>
>>>>This is a great machine. Two really independant VCOs!
>>>>
>>>>Johannes
>>>>
>>>>
>>>>gil_we wrote:
>>>>
>>>>
>>>>>Thanks very much !
>>>>>
>>>>>The tuning is bad on both VCO1 and VCO2 of that oscillator
>>>
>>>(although
>>>
>>>
>>>>>it seems more extreme on VCO2).
>>>>>
>>>>>I uploaded the schematics diagram for the VCO board to the files
>>>>>section - what would be the caps to check on that one ?
>>>>>
>>>>>Thanks again.
>>>>>
>>>>>
>>>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>>>
>>><johau@g...>
>>>
>>>
>>>>>wrote:
>>>>>
>>>>>
>>>>>
>>>>>>Hi,
>>>>>>
>>>>>>I only have the schematics for the MK I; which I do not know
>>>
>>>whether
>>>
>>>
>>>>>>it is similar to the MK II. Which VCO has the problem? Is it
>
> VCO-
>
>>>1 or
>>>
>>>
>>>>>>VCO-2 or both? If it is both then have a look at the hold
>>>
>>>capacitors
>>>
>>>
>>>>>>after the VCO CV demux IC15 (a 4051) on KLM-301 board. These
>
> are
>
>>>the
>>>
>>>
>>>>>>caps C25 - C32.
>>>>>>
>>>>>>Good luck,
>>>>>>
>>>>>>Johannes
>>>>>>
>>>>>>
>>>>>>gil_we wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>I've been recovering this one, found in the flea market.
>
> Overall
>
>>>it
>>>
>>>
>>>>>>>had about 8-9 different faults that I fixed, leaving two
>>>
>>>problems.
>>>
>>>
>>>>>>>The first is a bad SSM2056 chip which I need to find. The
>
> second
>
>>>i
>>>
>>>
>>>>>>>probably inherent in the discrete ciruit of the second
>>>
>>>oscillator.
>>>
>>>
>>>>>>>Upon powering it up, that particular oscillator will be out of
>>>
>>>tune,
>>>
>>>
>>>>>>>till it gets to its max. internal temperature where the tuning
>>>
>>>of
>>>
>>>
>>>>>>>that VCO is geting more or less - stable.
>>>>>>>
>>>>>>>All other oscillators are immediately in tune, no matter what
>
> is
>
>>>the
>>>
>>>
>>>>>>>temperatue inside the machine.
>>>>>>>
>>>>>>>I, of course, tried to figure out what the bad component is by
>>>>>>>blowing with a straw on each and each of the suspected
>>>
>>>compnents, but
>>>
>>>
>>>>>>>blowing on every component on the circuit of that oscialltor
>>>
>>>which
>>>
>>>
>>>>>>>seems to be pitch related, seems to effect the pitch.
>>>>>>>
>>>>>>>I also tried to switch transistors between the bad oscillator
>>>
>>>and
>>>
>>>
>>>>>>>another (working one) but the problem persisted.
>>>>>>>
>>>>>>>Does anyone have any other idea / direction ?
>>>>>>>
>>>>>>>Thanks
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>PolySix "Digiest" Page: http://www.acc.umu.se/~amber/Poly6
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>
>
>
>
>
>
>
> PolySix "Digiest" Page: http://www.acc.umu.se/~amber/Poly6
> Yahoo! Groups Links
>
>
>
>
>
>
>