Fonitronik PS3100 DIY

[scottpy]

Sorry for the double post here. I accidently posted this in the intro of this subforum.



Hey everyone! Does anyone have any experience building the Fonitronik PS3100? I am having an issue that's a head scratcher for me.

The top channel is just making pulsing sound regardless if I have anything in any input. The pulsing sound changes too if I have a gate source like a BeatStep Pro as any part of the signal chain and I change the tempo. The LED does not work either and I'm sure the polarity is right on it.

The other channels work just fine and summed output works but mixes in the pulsing from channel 1.

I have changed out the transistors on channel 1 as well as replaced the vactrol.

BTW, Q10 is mounted backwards from the silk screen as it's a J111.

Main Board Top
https://photos.app.goo.gl/JLh9fVA1JWcuJruB9

Main Board Vactrols
https://photos.app.goo.gl/NuAUbCuZa3A5kBSX6

Interface
https://photos.app.goo.gl/zvCz1R2DBTAgYBxd6


Appreciate any ideas you guys might have.

[emmaker]

I can't really tell but in the interface photo it looks like LED1 has the flat side (cathode) on the right side which is backwards.

Is it pulsing at the rate of the LFO?

Is the LFO woring right and putting out the proper signal?

Is the jack for the top channel disconnecting the LFO or is the LFO always connected.

When i see unwanted oscillations I start thinking about capacitors/capacitance and feedback. Is there something going on with those on the top channel.

Jay S.

[scottpy]

Jay,

Thanks for your reply! I really appreciate it.

I can't really tell but in the interface photo it looks like LED1 has the flat side (cathode) on the right side which is backwards.

I flipped the LED but there's no change. So definitely not pulsing with the LFO rate. The other two are.

Is the LFO woring right and putting out the proper signal?

I can confirm it's working. I can listen to channels 2 and 3 individually and all seems well. The LFO out is also working.

Is the jack for the top channel disconnecting the LFO or is the LFO always connected.

Unfortunately, I can't confirm this. The channel does nothing but provide pulses that are not tied to the cycle of the LFO.

When i see unwanted oscillations I start thinking about capacitors/capacitance and feedback. Is there something going on with those on the top channel.

That's very interesting! I replaced the transistors but maybe I have a bad capacitor on channel 1? Is there any way it could be the trimmer as well?

Mouser, here I come.

-Scott