Ganglion Channel 4 Producing Abnormal ERP Data (Other Channels OK)

Hello OpenBCI Community,

I am seeking advice on an issue I'm having with my Ganglion board where Channel 4 is consistently producing abnormal ERP data, while Channels 1, 2, and 3 appear to be functioning correctly.

I have already confirmed that all four DIP switches (SW1-4) on the board are in the DOWN position for standard EEG recording.

The Core Problem

The issue seems to be tied specifically to the Channel 4 input pin (+4) on the Ganglion itself, not the electrodes or cables. No matter which electrode location or physical cable I connect to Channel 4, the resulting ERP plot is corrupted and looks significantly different from the other channels.

Troubleshooting Steps & Evidence

To diagnose this, I have run multiple tests, including swapping the electrode inputs.

1. Test A: Fp2 connected to Channel 4

   • I connected the Fp2 electrode to the +4 input pin.
   • When plotting the ERPs (P300 and N400), the waveform from Channel 4 is very strange, while the plots from channels 1-3 (connected to other electrodes) look as expected.
   • (See attached image which shows the strange ERP from Channel 4 using these filter settings)
     • P300 filter: 0.2-10 Hz
     • N400 filter: 0.1-30 Hz
       

2. Test B: F8 connected to Channel 4

   • To ensure it wasn't a site-specific issue, I then connected the F8 electrode to the +4 input pin.
   • The problem persisted. The ERP from Channel 4 was again completely different and did not show the expected components. The other channels remained fine.
   • (See attached image showing the strange ERP from Channel 4 in this configuration)
     • Filter: 1Hz high-pass, 125Hz low-pass, 50Hz notch
       

To be clear: when I connect the Fp2 or F8 electrodes to any other channel input (e.g., +1, +2, or +3), they produce normal-looking data. The problem only occurs when an electrode is plugged into Channel 4.

My Questions

1. Given that the problem stays with the Channel 4 input pin regardless of the electrode used, does this strongly suggest a hardware fault with that specific channel on my Ganglion board?
2. Has anyone experienced an issue where a single channel on a Ganglion fails or produces consistently noisy/bad data while others work fine?
3. Are there any other software settings, firmware issues, or hardware configurations I should check that could cause just one channel to malfunction like this?

Any insights or suggestions for further testing would be greatly appreciated. Thank you!