Parasit Into The Unknown - Signal suddenly stops at CMOS chip...

[Sesh]

Hi there

I'm building a vero board clone of the Parasit - Into The Unkown from this layout: http://tagboardeffects.blogspot.com/2015/12/parasit-studio-into-unknown.html
Schematic: https://image.easyeda.com/histories/f0e601999238450c988951a000bd8c81.png

It's been lying in the bin for months.. but I took it up again and now I think I'm very close to cracking it after having double-checked component placement, checked for unwanted bridges and scored between the rows.

The LFO rate led flashes perfectly... there is voltage going 'round in the circuit.

It's the first CD4069 in the audio path that's bugging me (for starters). I've traced my signal with an audio probe to pin 13/input 6 (where it distorted as I reckon it's supposed to) - but it doesn't come out of output 7 (pin 12). I've tested for continuity to ground on the offending pin to see if it's shorted.. but that wasn't the case.

So here's some voltages:

CD4069:

1 3,44    14  8,42
2 3,89    13   0
3 0        12   8,42
4 8,42    11   8,42
5 0         10   0
6 8,42     9    0
7 0          8   8,42

[PRR]

> I've tested for continuity to ground on the offending pin, but nothing there.

"nothing"? No continuity? What does that even mean??

Use your numbers. A meter's "continuity" may be "under 100 Ohms". That's close enough to check trailer lights. But we electronics techs find significance in 200 or 500 Ohms.

[Sesh]

> I've tested for continuity to ground on the offending pin, but nothing there.

"nothing"? No continuity? What does that even mean??

Use your numbers. A meter's "continuity" may be "under 100 Ohms". That's close enough to check trailer lights. But we electronics techs find significance in 200 or 500 Ohms.

Thanks, but the pin is afaik not supposed to be grounded, so I was just checking for a short. That's what I meant. I edited to make this clear.

[anotherjim]

It looks like the vero layout doesn't use the same arrangement of inverters so doesn't match the schematic which is of the pcb version.
I think it's pins 11 & 12 on this layout - they should be linked and so read the same voltage.

[Sesh]

It looks like the vero layout doesn't use the same arrangement of inverters so doesn't match the schematic which is of the pcb version.
I think it's pins 11 & 12 on this layout - they should be linked and so read the same voltage.

My bad! I noted it wrong. It does indeed have the same voltage.. I edited It.

And you're right, the layout uses different input and output than the schematic, forgot to note that.

My big question is why the signal doesn't come efter the chip and comes out amplified at pin 12.. I tried swapping the chip for a fresh one, no dice

[anotherjim]

The Gate part uses a circuit known as a Schmitt Trigger. This uses positive feedback to make the output switch only when the input signal is strong enough to overcome the influence of the positive feedback. To get positive feedback, two inverters are wired in series. The Gate control pot sets how strong the input needs to be to get an output. Less input resistance makes it easier or most sensitive. You should definitely get a signal out with the pot at minimum resistance.
So check the feedback resistor isn't a lower value than it should be and that the Gate pot is working (you can resistance test the pot). Less feedback resistance makes it less sensitive to signal.

The signal input stages are very sensitive to noise pickup as they give a lot of amplification, so the gate control is needed to stop it from making random noises when you aren't actually playing.

[Sesh]

The Gate part uses a circuit known as a Schmitt Trigger. This uses positive feedback to make the output switch only when the input signal is strong enough to overcome the influence of the positive feedback. To get positive feedback, two inverters are wired in series. The Gate control pot sets how strong the input needs to be to get an output. Less input resistance makes it easier or most sensitive. You should definitely get a signal out with the pot at minimum resistance.
So check the feedback resistor isn't a lower value than it should be and that the Gate pot is working (you can resistance test the pot). Less feedback resistance makes it less sensitive to signal.

The signal input stages are very sensitive to noise pickup as they give a lot of amplification, so the gate control is needed to stop it from making random noises when you aren't actually playing.

Thanks! That's not the problem, tho. Signal does pass through the pot to pin 13.. Here I hear a distorted signal which should be about right. But it stays at the input (pin 13) and doesn't come out the output (pin 12).
The 1M resistor is also the right value.

I'm wondering why that particularly output doesn't work. I've concluded it's not the chip by replacing it. Is the chip not being supplied properly? Could there be a short?
I'm out of troubleshooting techniques  :/

[anotherjim]

If you think the inverter isn't working you can either...
Disconnect the 1M feedback resistor or...
If the chip is in a socket, take it out and bend the output pin outward, put it back in the socket then see if you get a signal on the pin or...
With the chip out, continuity test (DMM diode/beep) the socket pin to surrounding pins and strips to prove it isn't shorting to anything in reach.