ADSR V2 Sustain Always High

[Sebo]

Hi:
I recently build my second ADSR V2, the first worked OK, but this one have some trouble. Attack and Release works OK, but sustain is always high no matter the position of the pot.
I measured the gate after Q2 and is OK, but the signal after Q3 is not right, if I understood right it should be a pulse/trigger, but I'm meassuring a constant high signal with some sporadic very narrow pulses going to 0V.
I changed Q3, C4 and R10 with no luck, looked for shorts or breaks, but everything seems OK.
I tought to try a smaller cap (1nF), but I don't know why isn't working as it should.

[yusynth]

The behaviour you describe is normal, the signal at the collector of Q3 must be high with no gate and briefly go to 0V at the beginning of the GATE. The 555 is triggered by a falling edge.
Try and change the 555 that may be defective.

[Sebo]

I've already changed the 7555 (2 times) and didn't help.
I found another suspicious behaviour:
The output is very low about 3V (I'm not sure but at the begining of my test I think it was 10V, but I'm not sure).
The voltage between R12 y P4 is changing with the gate, also the Voltage at the other side of R12, that is conected to +15 is changing a little, I can't found any shorts or anything that justifies that.

[Sebo]

Hi Yves:
I found the problem, it was a short in the TL074 (in the LED circuit). It was har to find because was a short inside the socket.
Thanks a lot for the help.

[Blue Hell]

I love these detective stories

(Especially when they have a happy ending)

[yusynth]

Short in the socket, gee that was not an easy one to find Sebo !

[Sebo]

Yeah, and it was my fault, a little piece of copper from a multicore wire fall inside the socket, and when I inserted the chip gets trapped inside, I saw it by chance...