No resonance on 4 pole mission

Hi everybody.

I just mounted a 4PM kit and everything was fine until it wasn’t : my resonance is very very low.
i double checked everything : resistors and capacitors are the good ones, capacitors are not short cutted, powervoltages seems good.
The Q voltage is only 1,74V with full resonance whereas it goes up to 5V on my SRM4.

Thanks for any help for troubleshooting this.

The Q voltage range change is normal – the circuit is designed to handle very different resonance modes (with or without waveshaping diodes), so in liquid mode, the voltage on the Q pin is scaled down a bit.

The resonance control happens with the LM13700 and the resistors / capacitors below it. Check their soldering.

Post a detailed photo of your board, you might have swapped resistor values.

If you have a scope, check that the voltage on pin 4 of IC3 is a scaled down (1/10) version of the signal on pin 1 of IC6.

I checked the soldering and resistors/capa values again, didn’t see anything.
got nothing on pin4 of IC3.

here is a picture of my filterboard

What do you mean by “I got nothing on pin4 of IC3”? 0V? Not even noise? Could you post pics of your scope traces?

The first resistor below the LM13700 looks strange. Can you post a better picture zooming in this area? Does look brown, black, black orange…

Sorry, at pin4 i got 0V with voltage meter and no oscillation or noise with scope (i use the scope tool of my soundcard so i can’t see DC on it)
The first resistor below LM13700 is brown, black, black, orange, brown. A 100k e24.

What do you get at pin1 of IC6?

i got the mixed waveforms, if the scale of the motu’s scope is right (i’ll check that tomorrow), the waveform has an amplitude of approx 1,4V (just with osc 1/saw)

huh, the signal at pin1 of IC6 isn’t affected by the filter? It should be low-pass filtered by a 4-pole.

Finally got it : R31 was shorted so pin4 was at GND (don’t know why, i just desoldered and soldered the resistor)
Thanks for helping, know i’m gonna tune my 4PM and make it scream!