Particle B402/404 not detectable via USB but still provides requiste power

Hi there,

I have set up a custom LTE board using the M.2 SOM EVAL Board as a reference.
The usb provides the requisite power, meaning I can signal/ping/connect to the B402 particle via Cellular connection (LED blinks blue than remains a constant blue-connected). The problem is I can’t seem to connect via serial connection.
Interestingly enough the usb does connect successfully as it provides the required power and there is the distant sound when connecting and disconnecting the usb to the laptop itself.

I have checked the D-/D+ lines and there are no shorts.
I have the M.2 Eval board and have tried to compare testing results between the eval board and the custom one and there seem to be no distinct differences.

I can include the schematic of our board, but I was wondering if this was an issue that had been discussed already-I did go through a few of the related issues and if I remember correctly those who have difficulty connecting via usb, can’t connect online either.

Any help would be greatly appreciated.

p.s. ( I have 1 B404 and 2 B402 cards–> all of which have the same serial connectivity issue)

Thank you

twahidi

Did you connect the USB power pin to SoM pin 16, VUSB? On the nRF52 the USB interface is only activated when there is 5V on VUSB. When there is no power, the USB block in the MCU is turned off to save power.

Yes VUSB is connected to SoM pin 16. Voltage measured: 5.09v
VCC (pins 2-8): 4.16V
3V3 (pin10): 3.3V