Pico D4 unable to flash

[SimoneT]

Hi folks, I'm developing a custom Pico D4 board which has been prototyped.
Problem is that there is no communication with Pico, the CP2104 becomes visible but it is impossible to flash it:

Connecting........_____....._____....._____....._____....._____....._____....._____
A fatal error occurred: Failed to connect to ESP32: Timed out waiting for packet header
*** [upload] Error 2

Same result from PlatformIO or using esptool.py manually...

Things I tryed:
- Swapping 10uF capacitor on RST with a 1uF
- Removing pullup on GPIO0
- Manually trying to pull GPIO0 low while resetting
- Even removing the Pico to check that there are no solder bridges underneath

I know from the datasheet that GPIO2 and GPIO12 may be left floating since they have internal pullups/down
I cutted the jumper to leave GPIO16 unconnected.
Still no luck

Powering the board with 5V it is drawing +/-30mA which seems to be a little on the low side.

Would you mind having a look at my schematics and provide me with some feedback?

Thanks a lot!

[ESP_Sprite]

- Are you getting a proper 3.3V?
- If you open a terminal (or idf.py monitor) and you reset the ESP, do you get any chatter on the serial port?

EDIT: Think I found it: Your VDD3P3_RTC is not connected to 3.3V.

[SimoneT]

Hi,
- yes 3.3V stable
- no feedback in a terminal when resetting the board

[SimoneT]

I see thanks.
Do you think that not powering RTC may make the Pico unable to work properly?

[SimoneT]

I tryied soldering a very thin wire from the unconnected pin to 3,3V but it doesn't change.
Admittedly soldering a qfn pin to a wire is not that easy, under the microscope it seems ok but I may have made a bad joint...