Pepper Pot 7 dead

fr4nky

Hi everyone,

I'm working with a Bela Pepper module and have discovered that Pot 7 (analog input channel 7) is not responding at
all. I've done some debugging and wanted to check if anyone has experienced this or has suggestions before I dive
into hardware troubleshooting.

Symptoms:

Pot 7 consistently reads 0.000 (or very small noise values like -0.001)
Does not respond when turned fully clockwise or counter-clockwise
All other pots (0-6) work perfectly and show full range (0.000 to 1.000)

Configuration:
Powered via Eurorack 12V (not USB-only)
Analog channels: 8 (configured in IDE settings)
Jumpers: CV 4-7 set to ANALOG mode (not TRIGGER mode)
Tested with multiple different patches (simple pot reader, official Bela examples)

What I've Tested:
✅ Created a debug patch that reads all 8 analog inputs
✅ Verified pots 0-6 all work correctly (respond from 0.000 to 1.000)
✅ Pot 7 consistently shows 0.000 regardless of position
✅ Checked jumper configuration (CV 4-7 set to ANALOG, not TRIGGER)
✅ Power cycled multiple times
✅ Tested with Eurorack 12V power (not just USB)

Simple Test Code:

// Reading all 8 pots
for(int i = 0; i < 8; i++) {
float pot = analogRead(context, n/gAudioFramesPerAnalogFrame, i);
rt_printf("P%d:%.3f ", i, pot);
}
// Output: P0:0.894 P1:0.877 P2:0.890 P3:0.906 P4:0.875 P5:0.885 P6:0.896 P7:0.000

Questions:
Is this likely a hardware fault (broken pot or bad solder joint)?
Could there be a jumper or configuration I'm missing for channel 7 specifically?
Has anyone else experienced a single analog channel failing on Pepper?
Any suggestions for hardware diagnostics I should try before assuming it's broken?

I can work around it by using only 7 pots, but wanted to check if there's something obvious I'm missing or if this is
a known issue.

Thanks in advance for any help!

giuliomoro

You'd need to carefully remove the cape and BBB from the Pepper PCB and test the channel without the Pepper PCB attached, simply powered from USB. That will tell you whether the hardware failure is within the cape or the Pepper PCB.

fr4nky

thank you for the reply. could you please let me know a way to test the channel? i understand i need to remove the Pepper PCB . how would i test the channel within the cape - bread board / jumper wires and a pot ? thanks

giuliomoro

Just connect the channel via a jumper wire to pin P9.03 (labelled as 3v3 on the cape (if it's rev C) and in the pin diagram inside the IDE). Then you should read approximately 0.81 on it.

fr4nky

thank you will try this and let you know .

fr4nky

hi Giulio, so I have tested the cape and BBB as you said, and the channel is alive:
POTS: P0:0.002 P1:0.007 P2:0.074 P3:0.212 P4:0.014 P5:0.164 P6:0.303 P7:0.841

Could you please advise me on how I could test the pepper PCB? thank you

fr4nky

Above are some photos for you to see how I am powering up the Pepper via the Eurorack, ovs is also connected to the USB when I use the IDE. I wonder if I am doing anything wrong in these.

fr4nky

Hi Gulio i have made more tests, but no luck. I wanted to ask if you could look at this report, and maybe I could send this in for repair?

Bela Pepper Pot 7 Hardware Fault - Diagnostic Report

Symptom:

Pot 7 (P7, analog channel 7) always reads 0.000 in software regardless of physical position. All
other pots (0-6) function correctly.

Diagnostic Tests Performed:

Cape & BeagleBone Test (Bypassing Pepper PCB)
Removed Pepper PCB
Connected jumper wire from P9.40 (AIN7) to 3V3 rail
Result: Channel 7 reads correctly (0.841V)
Conclusion: Cape and BBB are functional ✅
Potentiometer Resistance Test
Measured pot 7 resistance with multimeter (unpowered)
Result: Pot changes resistance smoothly (0Ω to _10kΩ)
Conclusion: Potentiometer itself is functional ✅
Continuity Test (Wiper to Cape)
Tested continuity from pot 7 center pin (wiper) to cape connector
Result: Continuity confirmed ✅
Conclusion: Wiper signal path is intact ✅
Power Supply Voltage Test (System Powered)
Measured voltage across pot outer pins
Pot 6 (working): Left pin = 1.5V, Right pin = 0V
Pot 7 (broken): Left pin = 0V, Right pin = 0V
Conclusion: Pot 7 not receiving 1.5V power on left pin ❌
Power Rail Continuity Test
Tested continuity from pot 6 left pin → pot 7 left pin (unpowered)
Result: Continuity confirmed ✅
Conclusion: 1.5V power rail trace between pots is intact

---
Root Cause Identified:

Pot 7 left outer pin has no electrical connection to the 1.5V power rail despite physical continuity
along the trace.

Likely causes:
Cold solder joint at pot 7 left pin (poor connection under load)
PCB pad delamination at pot 7 left pin
Micro-crack in trace very close to pot 7 left pin pad

---
Repair Attempted:
Reflowed solder on pot 7 left outer pin with soldering iron
Result: No improvement - pot 7 left pin still reads 0V

---
Hardware Configuration Notes:
System powered via Eurorack 12V
CV inputs 4-7 jumpers set to ANALOG/CV mode (not TRIGGER)
All attenuator pots 0-6 confirmed working
---

giuliomoro

Here's the relevant portion of the schematic (full schematic at or https://github.com/BelaPlatform/bela-pepper/tree/master/Design%20Files/rev2b):

The configuration for "ANALOG IN" assumes that pins 2 and 3 of J12 are shorted with a jumper and pins 1 and 2 of J20 are shorted with a jumper (these are labelled as "analog" on the PCB).

"Left" and "right" nomenclature is hardly meaningful, considering it depends on which side you look at it. You can use the "GND" vs "R23" side from the diagram above.

On one outer pins of the pot you should get 0V and on the other one (if both jumpers are correct) you should get :

if no jack is plugged in: "VOLTAGE_SELECT_OUTPUT", which normally 10V
if a jack is plugged in: the voltage coming into the jack

fr4nky

Hi Giulio. I systematically tested Pot 7's signal path, starting from the Eurorack 12V power supply through the voltage selection circuit, jumper configuration (J12), and CV IN 8 jack, and confirmed that 10V was successfully reaching the jack terminals. However, when I measured all three pins on Pot 7 itself, they all read 0V, which told me there was a broken PCB trace or cold solder joint between the jack output and Pot 7's hot pin. I soldered a jumper wire directly from the CV IN 8 jack's 10V terminal to Pot 7 Pin 3, and now the pot reads 10V when turned fully right with varying voltages at the wiper, which definitively confirms the problem in the Pepper board's PCB traces or connections—not a component failure, jumper misconfiguration, or power issue. Could you please let me know if I could send this to have a look ?thank you

edit: I have identified the exact failure point (between jack and R23) and fixed the issue:

R23 did not receive V. I connected a jumper wire from the jack in 8 to the R23 left pin. Now it's all working. This suggests that the pepper board has a broken PCB trace.

POTS: P0:0.894 P1:0.877 P2:0.890 P3:0.906 P4:0.876 P5:0.885 P6:0.894 P7:0.902
POTS: P0:0.320 P1:0.439 P2:0.000 P3:0.000 P4:0.000 P5:0.000 P6:0.000 P7:0.000
POTS: P0:0.000 P1:0.000 P2:0.000 P3:0.000 P4:0.000 P5:0.000 P6:0.000 P7:0.000
POTS: P0:0.894 P1:0.878 P2:0.889 P3:0.906 P4:0.876 P5:0.884 P6:0.895 P7:0.902
POTS: P0:0.894 P1:0.878 P2:0.891 P3:0.906 P4:0.876 P5:0.884 P6:0.894 P7:0.902

giuliomoro

Good that you found the issue. Maybe one of the through hole pads was lifted or otherwise damaged during soldering.