Troubleshooting Yusynth Minimoog modules

sterio · Joined: May 24, 2019 Posts: 3 Location: Grenoble, France

Hey,

I'm building YuSynth minimoog VCF clone, but I have issues troubleshooting my module. I don't have any signal at the output. In fact, the signal the signal only reach the ouput of the U3b op amp. Then on the other lead of R6 (the first is connected to U3b's output), the signal is divided by 20. Then at the input of the differential pair I have no signal left, only DC.

The DC values on the pins of the differential pair U1b are really strange:
1: 2,5V
2: 0
3: 600mV
4: 10V
5: 10V

Here is the schematics

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

that you also can find here:
http://yusynth.net/Modular/Commun/MOOGVCF/Moogfilter-sch.jpg

Do you have any idea about what could be failing ? I spent countless hours trying to fix this issue and I can't think of what could be the problem. I doubled check every solder, components value, replaced U1 by another CA3086.

Oh, and the input is line signal from my Minibrute: it is more or less 2V peak to peak.

Thanks ! Laughing

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kkissinger · Posted: Sat May 25, 2019 7:03 am Post subject:

Temporarily disconnect the emphasis pot and see if that changes anything. Also, look for solder bridges that are inadvertently grounding your signal. Your 2v input signal is a bit on the low side, too.

Good luck!

sterio · Joined: May 24, 2019 Posts: 3 Location: Grenoble, France

Thanks ! I'll try that !

sterio · Joined: May 24, 2019 Posts: 3 Location: Grenoble, France

Unfortunately, disconnecting the emphasis pot didn't change anything. I double checked each and every solder joint, and looked for shorts but didn't find anything.

Also on pin 4 of the CA3086, I do have a very low signal in addition to the DC offset