[sdiy] EFM VCO 4e is fixed

[cs e]

I had the tempco double-grounded...whoops.  All I had to do was cut a jumper.

Thanks for the help, the mixer section/freq pot was bad - so thanks
for helping me fix that.

Now to see if this piece will calibrate.

Chris

On 2/28/08, cs e <modulemania at gmail.com> wrote:
> most of the old EFM docs (and the old forum copies) are here:
> http://www.modular.fonik.de/Page37.html
>
> So, after fixing the bad pot, the input mixer opamp (U1a) is
> outputting proper voltage. I think the input mixer section is
> working. Something else must be wrong.
>
>
>
> On 2/28/08, Dave Magnuson <resonant at hoohahrecords.com> wrote:
> > I don't have a copy of the VCO4e schematics, so I'm hoping it's similar to
> > revision 4D.
> >
> > You mention "magic smoke" coming from your freq pot - sounds like you may
> > have cooked it. Check voltage at the wiper to see if it still swings from
> > v- to v+.
> >
> > One possible cause would be a short in the CV mixing section - look for a
> > solder bridge in there somewhere. If the mixer was shorted to ground, for
> > example, you may have just connected V+ to ground through your pot - hence
> > the smoke. You may have also dripped some solder in the back of the pot...
> > or you may have a frayed wire. You could also have a cracked trace / bad
> > joint... or a bad opamp.
> >
> > Start your troubleshooting at the mixer inputs - see if you're getting a
> > swing in voltage from the pot and CV inputs (check at the op amp input).
> > If you're getting a voltage swing at the input, check the output... you
> > should also see the voltage swing here. (You should be able to use your
> DMM
> > for this).
> >
> > Make sure you have V+, V- and ground at the appropriate pins of the opamp.
> >
> > If the FM input is working, it's likely that the expo pair is doing
> > something... so start with the opamp... reply with what you've found, and
> > the list could probably help you get that thing working.
> >
> > Dave Magnuson
> >
> > ----- Original Message -----
> > From: "cs e" <modulemania at gmail.com>
> > To: <synth-diy at dropmix.xs4all.nl>
> > Sent: Thursday, February 28, 2008 7:29 PM
> > Subject: [sdiy] EFM VCO 4e is singing a fixed frequency
> >
> >
> > > I've got the EFM VCO 4e singing, but at a fixed frequency.
> > > The problem is the frequency can't be adjusted - by knob or any CV
> inputs.
> > >
> > > It hard syncs to ext VCO, FM-in works, PWM and all waveforms look OK.
> > > What would be stopping this thing from letting its frequency be
> > > adjusted? I hope the CV inputs OpAmp isn't bad - that would be my
> > > luck though, because I didn't use a socket on that one :-(
> > >
> > > Little side note - while looking at some voltages with the scope and
> > > the DMM, I saw a little magic smoke coming from the "FREQ" pot (the
> > > one with +/-15V and the wiper going to the pcb).
> > >
> > > Any troubleshooting tips here?
> > >
> > > Chris
> > > _______________________________________________
> > > Synth-diy mailing list
> > > Synth-diy at dropmix.xs4all.nl
> > > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >
> >
>