Fine Tune Filter

I meant that you should do the power test from step 5 of the build instructions for the filter again. If the power supply is not providing the -5V anymore that would be an obvious reason why the signal is not making it to point two and beyond.

l did the test from step 5 of the instructions (again), and the voltage of the red dots is 5, but the voltage of the green dots is 0.620

I cleaned and resoldered some points, synth now sounds, but I have the problem with the voltage.

What is the voltage you get on each pin of the 7905?

input voltage in 7905= 152,2
output voltage in 7905=0,472

152.2 what? I doubt it’s volts!

to clear things up, how I measure the voltage on the 7905?

Read here

Input 7805

Output 7805


Output 7905

Have you checked your Meters Batteries? Wait, is the 7905 0,474??? And: did you use Lötfett?

I resolved the problem, was the IC2 (LT1054), bad contact.

the filter oscilated itself, i’m go to tune, thanks a lot to everyone.

the problem is not completely solved, sometimes the synth sounds, sometimes not.
The LT1054 may be damaged?

Synth sounds when the voltages are fine but when no sounds I measure the 7905 and I get the strange voltages.

It’s most likely a problem with bad contact or bad solder joints in the region of LT1054 and 7905.

I discovered that when I discharge the electrolytic caps touching the positive with negative in the DC input with a metal, the synth sounds.
Why this should be and how can I fix it?

I’m not sure I follow what’s going on here…

What’s the problem exactly? No sound at all all the time, or no sound at all when you are trying to get the filter to self-oscillate with both oscillators disabled?

Have you tried tracing the signal chain as explained at the end of the build instructions?