PWR_ON pull-down too strong (R9 = 10k) - modem won't switch on
On the prototype, the PWR_ON signal has a PD and PU of each 10k; PU goes to 1V8. For switching on, the resulting 0,9V are not enough to power up the modem. By replacing the PD (10k) to 100k, the modem went on as expected.
Let's replace this 10k R with a weak PD.