@David_Kirk I will reply to myself then.
I have fixed this by swapping the mains powered USB HD, with a USB-powered 4Tb Toshiba portable HD. Smaller drive (physically), but now uses the USB power from the Pi. The Pi wakes it up as normal, and it works as it should.

@madbrain

Hi there, I had the same problem as you. I couldn't get the Pi3 composite output working with overscan for Recalbox. I've spent quite a while figuring this out on my Pi3 but I think I've got it.

It may be contradictory in some places, but please set your config.txt in the following way, making sure that each line is in this exact order:

[pi3] # Raise the first security limit up to 70 instead of 60 for pi3 temp_soft_limit=70 enable_tvout=1 #NTSC-480i sdtv_mode=0 #NTSC-240p #sdtv_mode=16 #PAL-576i #sdtv_mode=2 #PAL-256p #sdtv_mode=18 #4:3 sdtv_aspect=1 #16:9 #sdtv_aspect=3 disable_overscan=1 #this is on purpose hdmi_force_hotplug=0 hdmi_ignore_hotplug=1 dtoverlay=vc4-fkms-v3d #fkms not kms overscan_top=32 overscan_bottom=32 overscan_left=32 overscan_right=32 include crt/recalbox-crt-config.txt

Uncomment (delete #) from the start of the line for the resolution and mode you need. It is also important that you have 'fkms' instead of 'kms'. You will likely need to adjust the overscan values to the desired amounts after testing a few times. For me (Sony Trinitron) I used -14, -5, 13, 25 respectively. You can also use overscan_scale=0 instead of the four individual values and see if that's better for you.

Additionally, you have to edit the file cmdline.txt. The entry is a single line and must stay that way. At the end of the existing text, add:

video=Composite-1:720x480@60ie

for NTSC-480i.

For NTSC-240p you will need to keep 720x480 but the end should say @60e (no i means no interlacing). Setting 720x240p here will cause the image to only appear across the upper half of the screen.

Likewise, for PAL-576i, it's 720x576@50ie. For PAL-256p it's 720x576@50e.

I hope this helps you and anyone else with this issue.
P.S. I think updating Recalbox will reset all this. Might be better to put it into recalbox-crt-config.txt but I'll cross that bridge when I get to it.

Well, i have downloaded version 8.0 from this website :
https://archive.org/download/thc-recalbox

I have modify the cmdline.txt with this : video=HDMI-A-1:D video=HDMI-A-2:D (source : https://forum.recalbox.com/topic/26323/recalbox-8-x-sur-pi3)

And with this version 8.0, it works !!!

When wifi was set up, i have selected update from the update menu.
It has downloaded version 8.1.1 and installed it offline ... and then ... nothing ...

Seems like if this version 8.1.1 doesn't work 😞