Your knobs and panel acting as an antenna suggests they are not connected to
0V.
Specifically, I don't know where the fault/break is. I've never seen it
before. As I mentioned before, you have a working example next to you. Set
the knobs on the two to the same positions, then get in there with your
meter, and read the voltages at various points, and compare them.
From most checks, you can connect the black probe to 0V, and poke around
with the red probe.
For 0V checks, connect the red probe to 15V, and poke around with the black.
You should always get 15V (or very very close to it) as your reading.
Ken
Ken Stone sasami@... otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
0V.
Specifically, I don't know where the fault/break is. I've never seen it
before. As I mentioned before, you have a working example next to you. Set
the knobs on the two to the same positions, then get in there with your
meter, and read the voltages at various points, and compare them.
From most checks, you can connect the black probe to 0V, and poke around
with the red probe.
For 0V checks, connect the red probe to 15V, and poke around with the black.
You should always get 15V (or very very close to it) as your reading.
Ken
>Hi Kenbut the Fine Tune was functioning exactly the same as Frequency.Â
>
>Just wanted to update what i said about the VCO ; if it makes any difference.
>
>With the Tempco disconnected On the GND rail side , the whole thing worked
>Diophantine Wiring diagrams.
>The connections are : Fine Tune wiper to Tune , Freq to 1V/Oct as in the
>there is white noise and radio signals when i touch the knobs or panel.
>I have reconnected the Tempco and it's back to not working. In this state
>; all connection are correct.
>Also persistent Earth Hum.
>
>I have resoldered all of the board connections , there are no damaged pads
>I'm stumped.
>Tune : 0.3V
>1V/Oct Freq : -14.87
>1V Oct Input : -3.4
>
>This is the fourth one of these i've built , the one next to it is perfect.
>output.
>
>
>________________________________
> From: "sasami@..." <sasami@...>
>To: cgs_synth@yahoogroups.com
>Sent: Sunday, November 4, 2012 11:06 PM
>Subject: Re: [cgs_synth] Re: a couple of CGS48 VCO questions
>
>
>Â
>Usually, it is EXTREMELY unlikely that it is a damaged part. You probably
>have shorted two pads together/broken a pad by soldering for too long/used
>the wrong part somewhere. The tempco forms part of a voltage divider, so at
>a guess you have a wrong part (or other damage) around IC1 (TL072).
>
>First step: always check you have power on the pins of the IC.
>Second step: Make sure the "Trim zero" trim pot is near its center, not
>wound all the way up one end.
>Watch what happens at pin 7 of that TL072. It is the output of the input
>mixer stage.
>Possible help: You have two vcos. With them wired to exactly the same CVs
>(or using their tune pots set to the same positions) start comparing
>voltages between the two.
>
>
>>Hi Gary and all
>>
>>Just an update on the one i referred to as the 'Second VCO' that had no
>>wrote:
>>I changed out the TL072's , no change ; then the LM394 which i thought had
>blown.ÃÂ
>>
>>Doing that i discovered that it's working , but only when the Tempco is
>desoldered ( i desoldered the pad which is on the track that connects to Pin
>7 of the LM394).
>>
>>I'm stumped.
>>
>>If it makes any difference , the VCO wiring diagram i followed was from
>this page from diophantine :
>>
>>http://www.diophantine.net/synth/bocgs/bocgs-wiring.html
>>
>>
>>
>>
>>________________________________
>> From: Mongo <zathrus1@...>
>>To: cgs_synth@yahoogroups.com
>>Sent: Sunday, November 4, 2012 2:44 AM
>>Subject: [cgs_synth] Re: a couple of CGS48 VCO questions
>>
>>
>>ÃÂ
>>
>>Regarding the first VCO, it sounds like you probably have a bad IC1, or a
>bad solder joint somewhere. Recheck your solder joints, and if everything
>looks ok, measure the voltage at pin 7 of IC1 - it should track when the
>incoming control voltage changes. If it doesn't, try replacing IC1.
>>
>>On the second one, it's possible that the VCO is actually running, but just
>at a very low frequency. I had that happen on a Teezer VCO once. I'd
>definitely suggest replacing the TL072 - you were running it without power,
>so who knows what happened inside that little fellow.
>>
>>Gary
>>
>>--- In cgs_synth@yahoogroups.com, Stephen Richards <okayjustalittle@...>
>>>_______________________________________________________________________
>>> Hi Ken and all
>>>
>>> I'm building up the BOG panel and have done the two VCO's but am
>experiencing a few problems with both.
>>>
>>> One VCO is working fine apart from VC Freq pot ; seems to have
>zeroÃÂ effectÃÂ on the Frequency when fed CV and when turned ; it also cuts
>out at the very lowest range , shorting to some sort of low droning sound.
>>>
>>> The Second VCO has no output , no change when Freq pot is moved but when
>FM'd , PWM'd or CV is applied the the Variable CV input , i'm getting sound
>from the outputs.
>>>
>>> When i checked this Second VCO , i found i had only soldered Pins 1 and 5
>of the TL072 directly above the unicorn figure.
>>>
>>> Could this have caused damage to other parts of the circuit ?
>>>
>>>
>>> [Non-text portions of this message have been removed]
>>>
>>
>>
>>
>>
>>[Non-text portions of this message have been removed]
>>
>>
>>
>>------------------------------------
>>
>>The CGS Modular Synth home page: http://www.cgs.synth.net/
>>Yahoo! Groups Links
>>
>>
>>
>>
>__________________________________________________________
>Ken Stone sasami@... otherunicorn@...
>Modular Synth PCBs for sale <http://www.cgs.synth.net/>
>Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>
>
>
>
>[Non-text portions of this message have been removed]
>
>
>
>------------------------------------
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>Yahoo! Groups Links
>
>
>
>
Ken Stone sasami@... otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>