I think you need to take it a step at a time. Please provide answers for
each question. Just work with the 5V DC supply in this arrangement to remove
one whole set of variables.
(1) If the LEDs are correct, then you are booting.
Okay, my bad. I had assumed that if I wasn't seeing any serial
console traffic, then the unit was not booting. I bought an HDMI
cable today and connected a monitor to the board, powered up with a 5
V adapter, and lo and behold, I saw U-boot and kernel boot messages,
and eventually an Angstrom login prompt came up on the (HDMI) screen.
I then plugged in a USB Ethernet interface and rebooted, and was able
to SSH in.
So ... I see U-boot on the serial console if a monitor is plugged in
to HDMI *or* if the OTG is plugged in to a host.
Very sorry I didn't think to investigate with an HDMI monitor before;
it didn't occur to me that lack of serial console output could mean
anything other than the unit not working.
But I'll answer a couple of the still-relevant points for good
(2) I suggest you read Section 13 of the System Reference Manual and make
sure that you have the correct serial cable connections and that everything
is inserted corectly, ribbon cable not installed backwards. Does this all
check out OK?
My serial cable and other connections are definitely correct. I
haven't checked voltages at the various voltage access points on the
board, but at this point I'm thinking that isn't necessary.
Incidentally, I do seem to be experiencing random USB disconnects as
described in 14.0 of the manual. I'll try the fix suggested there.
USB usually lasts only a couple of minutes before it disappears.
(7) Has the board ever worked for you? You seem to say it works on OTG, but
it is not clear. It sounds like it boots from a powerd HUB. If the HUB is
not powered, then it must be plugged into a PC or there is no power. Some
PCs cannot deliver the full power requiremnts even though they should.
The board has always worked if it's powered via a powered USB hub that
is plugged in to a host. If the hub is just powered, (or if I use a
USB cable with pins 2+3 removed) I get no console.