UART / U-boot serial readout issues on HH5A

I'm trying to make a first-flash of LEDE onto my HH5A, using Ubuntu (pl2303hx usb adapter, picocom, tftp and cat). The wires are soldered in place (R77, R78, R45 and a ground pin), and a picocom readily displays the initial lines of bootup (whether CFG06 or CFG04 mode). But it stops showing anything more after this:

ROM VER: 1.1.4
CFG 06
DDR autotuning Rev 0.3d
DDR size from 0xa0000000 - 0xa7ffffff
DDR check ok... start booting... 

The router, however, continues booting - the lights change colour and lashing pattern, the WiFi network comes up, and I can even log into the admin page. Why am I not seeing anything else in my serial console?

I'm seeing the same behaviour on two different HH5As, and two different Ubuntu systems. The pl2303hx adapter looks like this.

I'd love any pointers people may have!

Did you successfully install LEDE? I'm pretty sure the original firmware doesn't get more talkative than that.

Make sure the BootSel2 is connected to ground during power on. The boot will stop at CFG04.
I just installed LEDE on my BTHH5a. It was painful because new linux kernel does not allow concurrent access to /dev/ttyUSB0.

Here are my instructions for serial boot:

Prerequisites: TFTP server, picocom
LEDE custom U-boot: lede-lantiq-bthomehubv5a_ram-u-boot.asc
LEDE HH5A installation image: lede-lantiq-xrx200-BTHOMEHUBV5A-installimage.bin
the installation image has to be placed in the tftp root directory

Serial Boot:

1) start picocom on the host computer:
   picocom -b 115200 /dev/ttyUSB0 --send-cmd “ascii-xfr -s -n”
2) boot with boot_sel2 low short time until CFG 04 shows up - force a boot of an ascii image
3) in picocom press Ctrl+a Ctrl+s to trigger send file and input the ascii image file name (make sure you use full path)
4) after file transfer is complete the image is booted and a root prompt shows up
5) on the serial terminal download a bigger more fully featured install image to RAM using tftp (this isn’t permanent)
  tftpboot 0x81000000 lede-lantiq-xrx200-BTHOMEHUBV5A-installimage.bin
6) on the serial terminal boot that image. image takes up to 4 minutes to boot. Again, nothing permanent
  bootm 0x81000000

After serial boot, do the nand backup and install as per manual. put a copy of the “lede-lantiq-xrx200-BTHOMEHUBV5A-squashfs-sysupgrade.bin” on the flashdrive before mounting it on the BTHH5a.