Doepfer

hello,

i checked the service manual of the a126 and i think
that i found the possible reasons for the malfunction,
but these should only occour with the first two
production series of the a126. a freshly
purchased a126 shouldn't have these problems
and should be returned for service in that case.

this is a rough translation from german to english,
i apologize for possible errors. if somebody is
interested, i can post the full text in german.
i guess this is ok, dieter?

1. check the ic5 and ic9 on the pcb. if these are tl064,
then maybe they should be replaced with tl084.

2. the sine/cosine vco is built around a cem3382,
which works correctly in a range of 50 - 5000 hz.
however, if you turn the freq knob fully cw and
apply a control voltage, you may go beyond these
limits and the cem3382 stops oscillating.
this happens when the voltage applied to the cem3382 ic
exceeds +6 volts. to prevent this, a 5.6 volts zener diode
has to be inserted between ground and the voltage inputs
of the cem3382 (the anode to ground).

3. when the a126 is modulated with a square wave at
audio frequencies, then under rare circumstances the
cem3382 stops oscillating too. this can be prevented
by adding a 1nf capacitor between r51 and p12.

hope this helps clearing up the issue.

best wishes

ingo



--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" 
<timothy@t...> wrote:
>
> I'm not aware of any problem like this with mine, but from memory, 
> the amplitude of the internal oscillator takes a while to settle 
down 
> after a CV change, and so (I'm guessing here) maybe at high CV it 
is 
> possible that it might stop running completely. I'll check it out 
> later today and report back then...
> 
> Tim
> 
> > same problem with mine,
> > anyone got a solution to it..?
> > 
> > /daniel
> > 
> > 
> > 
> > 
> > --- In Doepfer_a100@yahoogroups.com, "Tommy DOG" <mrsvomit@t...> 
> wrote:
> > >
> > > Then mine does too.
> > > It's always behaved like that.
> > > 
> > > TD
> > > 
> > > --- In Doepfer_a100@yahoogroups.com, Bakis Sirros 
> <synth_freak_2000@y...> 
> > wrote:
> > > >
> > > > hello zoran,
> > > > it seems to me that your a126 vcfs needs repair.
> > > > bakis.
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > --- Zoran Bosnjak <dj_allin@h...> wrote:
> > > > 
> > > > > 
> > > > > Hello,
> > > > > 
> > > > > I purchased A-126 VCFS (Frequency Shifter) recently,
> > > > > and I noticed that when 
> > > > > rotating Shift knob towards value 10, and applying
> > > > > control voltage to CV1, 
> > > > > the module stops functioning. I have to turn the
> > > > > whole case off and on, to 
> > > > > reset it and have it work again.
> > > > > 
> > > > > Is this behaviour by design or my unit is faulty ?
> > > > > 
> > > > > Regards,
> > > > > 
> > > > > Zoran
> > > > > 
> > > > > 
> > > > > 
> > > > 
> > > > 
> > > > Bakis Sirros
> > > > Parallel Worlds
> > > > Athens-Greece
> > > > [Doepfer_a100] group owner
> > > > http://www.shimarecords.co.uk
> > > > http://www.rubber.gr
> > > > 
> > > > 
> > > > 		
> > > > __________________________________ 
> > > > Yahoo! FareChase: Search multiple travel sites in one click.
> > > > http://farechase.yahoo.com
> > > >
> > >
> >
>