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Thread
2015-08-16 by Stephen Richards
2015-08-16 by Ken Stone
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 ?
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2015-08-16 by Stephen Richards
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 ?
2015-08-16 by Ken Stone
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 ?
--
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2015-08-16 by Stephen Richards
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 ?
--
2015-08-20 by Stephen Richards
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 ?
--
2015-08-20 by Ken Stone
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 ?
--
--
--
2015-08-20 by Stephen Richards
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 ?
--
--
--
2015-08-20 by Stephen Richards
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 ?
--
--
--
2015-08-26 by Stephen Richards
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 ?
--
--
--
2015-08-26 by Ken Stone
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 ?
--
--
--
--
2015-08-27 by Stephen Richards
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 ?
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2015-08-27 by babysealclub
Print a copy of the pcb art work. Test each trace and then highlight that trace on the print out. I usually probe component legs, then I'm also checking the soldering. Good Luck!
-TF
2015-08-27 by Dmitri SFC
2015-08-27 by Stevie Richards
On 28 Aug 2015, at 3:23 am, "Dmitri SFC dankedout415@... [cgs_synth]" <cgs_synth@yahoogroups.com> wrote:
2015-08-28 by kevin siegenthaler
On Thu, 8/27/15, Dmitri SFC dankedout415@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:
Subject: [cgs_synth] Re: CGS48 VCO problem
To: cgs_synth@yahoogroups.com
Date: Thursday, August 27, 2015, 10:23 AM
make sure the tempco is coupled
to the transistor pair.
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2015-09-02 by Stephen Richards
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 ?
--
--
--
2015-09-02 by Ken Stone
On Wed, Sep 2, 2015 at 3:29 PM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:I've completely removed the CGS48 pcb from the panel.Checked with backlight , repaired one borderline track (that led eventually to the LM394) with a link.It was one leg of the 100n just after the FM AC pad.Before i go and solder it back in ; can i power it up and test it as is ?
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 ?
--
--
--
--
--
2015-09-02 by Stephen Richards
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 ?
--
--
--
2015-09-02 by Ken Stone
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 ?
--
--
--
--
--
2015-09-02 by Stephen Richards
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 ?
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--
--
--
2015-09-03 by Ken Stone
On Thu, Sep 3, 2015 at 10:46 AM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote: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
Make sure the wires to the panel controls aren't tightly bundled with something that could cause interaction.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 ?
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2015-09-03 by eidorian_aladan_net
I've gotten so frustrated that I actually pulled some of my hair out, but not very often, and never with any of your boards Ken :)
Cheers,
A.
On 2015-09-03 12:13, Ken Stone otherunicorn@gmail.com [cgs_synth] wrote:
promise me you won't pull your hair out!
On Thu, Sep 3, 2015 at 10:46 AM, Stephen Richards okayjustalittle@yahoo.com [cgs_synth] <cgs_synth@yahoogroups.com> wrote:
Its was the pot after all that. Thanks Ken
From: "Ken Stone otherunicorn@gmail.com [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
Make sure the wires to the panel controls aren't tightly bundled with something that could cause interaction.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@yahoo.com [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@gmail.com [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@yahoo.com [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@yahoo.com [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@gmail.com [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@yahoo.com [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@gmail.com [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@yahoo.com [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@gmail.com [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@yahoo.com [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 ?
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2015-09-03 by Stevie Richards
On 3 Sep 2015, at 12:43 pm, "Ken Stone otherunicorn@... [cgs_synth]" <cgs_synth@yahoogroups.com> wrote:
promise me you won't pull your hair out!On Thu, Sep 3, 2015 at 10:46 AM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote: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
Make sure the wires to the panel controls aren't tightly bundled with something that could cause interaction.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 ?
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