Why the power supply self-osc?

Hi, All,
I developed a gsm-module.
It seems good with 1.5m power supply wire.
But when the power supply wire is about 10m length, my module can't startup and I can hear click noise every several seconds.
I guess the power supply self-osc, right?
And how to fix it?
Best,
Tony Liu



See the SCH as following.
And the power supply converter IC is LT8390.

Hi,

Use a scope and measure the voltage as close as possible to the GSM module.
I assume it is below specified min value ... at least for a short time.

Klaus