Its was the pot after all that. Thanks Ken
From: "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com>
To: cgs_synth@yahoogroups.com
Sent: Thursday, September 3, 2015 9:17 AM
Subject: Re: [cgs_synth] CGS48 VCO problem
To: cgs_synth@yahoogroups.com
Sent: Thursday, September 3, 2015 9:17 AM
Subject: Re: [cgs_synth] CGS48 VCO problem
It could be. Try that first.
Also:Try new power wires back to the PSU.
On Thu, Sep 3, 2015 at 8:51 AM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:
Hi Ken After removing and careful studying the PCB , i tested it. It seemed stable. Then when i put it back in the panel it started warbling again.Do you think this could maybe be a stuffed Freq Pot ?
From: "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com>
To: cgs_synth@yahoogroups.com
Sent: Thursday, August 27, 2015 10:41 AM
Subject: Re: [cgs_synth] CGS48 VCO problem
Correct. Pin 7 of the stable VCO goes to the lifted end of the 56k on the bad VCO. Note that it may sound a little flat as you will have two loads on pin7.On Thu, Aug 27, 2015 at 10:16 AM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Hi Ken, I still haven't solved the mystery of the warbling CGS48 VCO.If i was to test the core of the faulty VCO with the mixer section of the good VCO should i lift one side of the 56K resistor and clip the signal directly from pin 7 of the TL072 of the good VCO ? Just trying to get my head around this.
From: "Stephen Richards okayjustalittle@... [cgs_synth]" <cgs_synth@yahoogroups.com>
To: "cgs_synth@yahoogroups.com" <cgs_synth@yahoogroups.com>
Sent: Thursday, August 20, 2015 2:42 PM
Subject: Re: [cgs_synth] CGS48 VCO problem
I'll try, so pin 7 of TL072 of stable VCO to bad VCO ?I just can't understand what it could be if it's before that TL072.
On 20 Aug 2015, at 2:28 pm, "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com> wrote:I doubt it. The earlier test suggests that the problem is with the mixer. Have you tried driving the drifting core from the mixer of the stable VCO?On Thu, Aug 20, 2015 at 12:11 PM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Hi Ken, This thing is still causing me grief. Supply voltages at chips are fine. Could that 2N4856 be a problem ?
From: "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com>
To: cgs_synth@yahoogroups.com
Sent: Sunday, August 16, 2015 5:54 PM
Subject: Re: [cgs_synth] CGS48 VCO problem
Yes, it could be a failed span trimmer. Is there some reason you suspect it?On Sun, Aug 16, 2015 at 3:31 PM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Voltage on Pin 7 of that TL072 is fluctuating in time with the pitch. CA3140 has 15V on Pin 7 and -15V on Pin 4.When i feed Pin 7 of that TL072 to the good VCO , it warbles. Could this be a failed 10K SPAN Trimmer ?
From: "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com>
To: cgs_synth@yahoogroups.com
Sent: Sunday, August 16, 2015 2:50 PM
Subject: Re: [cgs_synth] CGS48 VCO problem
Check you are not picking up interference on the sync line. Perhaps swap the CA3140, which is the most vulnerable chip in the VCO.the first thing is to work out where it is occurring.Take the voltage from pin 7 of the TL072 that is connected to the 56k feeding the LM394. Monitor it on a scope, or feed it into the CV input of the other VCO. If it warbles, you problem is likely to be in the mixer stage. If the voltage on pin 7 is steady, it's the core having issues.
Clean off any flux that may be left on the rear of the board.
Check the supply voltage AT THE CHIPS.On Sun, Aug 16, 2015 at 2:14 PM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Hi Ken and all,One of my CGS48 VCO's has suddenly started completely loosing control of pitch.Every output is displaying the same behaviour. The pitch is wavering like a mosquito and occasionally jumps or drops dramatically in pitch.Supply voltage is fine , chips seem fine. I swapped the LM394s from my working VCO , no change.FM, PWM and SINE TO SAW shaper all working.Any ideas where i could start testing ?
--
--
--
--
--