Please help me troubleshoot a (seemingly) faulty Frames

Hi!

So I’m having a bit of a problem with a Frames I bought used and I was wondering if someone might be able to help me out please? I’m struggling to narrow down where the fault lies. I do this:

  1. FRAME knob full CCW, all VCAs set to 0
  2. FRAME knob full CW, VCAs set to some non-zero value (2 o’clock works best)
  3. Rotate FRAME from full CCW to full CW (both via FRAME knob or modulation input)

Output 3 and 4 smoothly change.
Output 1 seems to come on too hot too, too early and stutters like morse code after that.
Output 2 doesn’t come on until 12 o’clock and then it comes on full.
The LEDs match the audio out.

If I rotate VCA 1 and 2 manually they output as expected, as do their LEDs.

However if I switch the +10V on and take a look with the Mordax DATA oscilloscope Output 4 also seems to be acted unexpectedly:

Output 1 acts the same - smooth from CCW to 11 o’clock where it starts glitching
Output 2 acts the same - switches from 0V to 4V at 12 o’clock like it’s gated
Output 3 smoothly adjusts - 0V to 4V
Output 4 smoothly adjusts - 0V to 0.75V

The signal path seems to be the same either when manually adjusting the VCAs or controlling them via the Frame knob so it’s left me baffled!

EDIT: Because the LEDs reflect the audio, and because they are controlled from different output pins on the STM32 to the MOSI output, I am wondering if it’s the microcontroller that’s faulty…

EDIT2: I re-flashed with v1.2 just to make double sure there hadn’t been any corruption. Still have the same issues.

It looks like a different interpolation curve is selected for each channel – the one with bounce for channel 1, and the steppy one for channel 2.

It also looks like the exponential (and not linear) response is selected for channel 4, which explains why it doesn’t reach the same amplitude as the adjacent channels.

Oh that’s brilliant, thank you!! That’s done it!

I feel a bit of a fool now :laughing: but I enjoyed the mental workout :grin: