The input voltage to the 7912 regulator is -22.2V. I replaced the new regulators with the old ones (made by Texas Instruments), I now have -12.25V as output for the 7912. I measured the voltages at the pins. The new 7912 was a L7912ACV.
--- In vintagesynthrepair@yahoogroups.com, Hugh Vartanian wrote:
>
> On the regulator problem, what is the input voltage to the 7912? More
> importantly, what are you using for a ground reference? Measure right at
> the regulator terminals, in and out, to its ground pin. Neg 14.xx volts
> might be a result of a loose ground floating positive a bit when power is
> applied. Remove power and the positive current draw and the 'ground'
> makes its way back to ground..... Just a thought.
> -Hugh
> On May 19, 2013 5:36 AM, "Mikael" >
> > **
> >
> >
> > Hi all!
> >
> > I bought a rare Crumar Composer I while ago but it has some problems. This
> > synth has a mono synth section, a poly synth section, a organ section and a
> > string section. All these sections can be combined. There is a separate
> > output for every section and a main output. The separate outputs work but
> > the volume for the main output and the main output itself do not work,
> > could this be a problem in an amp-sircuit or something?
> >
> > The problem I'm trying to look at now and ask about is an issue with the
> > poly synth section. The problem is that the attack for the envelope is VERY
> > slow, I can change the attack rate on the front panel pot but the fastest
> > attack is about 15 seconds. Can anybody give me a hint where to look for
> > the problem? Also there is a pop when I release the key on all keys it
> > seems. The envelope of the poly-synth section is generated by a CEM3310
> > chip. There are also CEM3320 and 3330 chips on the poly section.
> >
> > Last problem I';m having is that the release rate for the organ section is
> > very sensitive, it seems that the effective range is about 30 degrees
> > (1-1.5 on a scale from 1-10), if I turn the pot about 40 degrees I have a
> > VERY long release time.
> >
> > I would really like to get this synth in shape, it sounds so good and it's
> > very rare, I think Crumar made only 500 of these.
> >
> > Thanks in advance!
> >
> >
>; >
>
Message
Re: [vintagesynthrepair] Re: Envelope problem, pops and "sensitive" pots (Crumar Composer)
2013-05-27 by Hugh Vartanian
Sounds like you have solved the regulator problem; no idea why the other part didn't work, assuming it was installed ok. Strange to have a defective part like that.
I deleted the rest of the thread; post a link to the schematics if you still need some thoughts on the other issues.
Hugh
On Fri, May 24, 2013 at 5:14 AM, Mikael <wmc_mick@...> wrote: