[Arm-netbook] EOMA68-A20, MD 1.7 severe Power Problems

[Pablo Rath]

>On Sun, Jul 26, 2020 at 10:54:27AM +0100, Luke Kenneth Casson Leighton wrote:
>> On Sun, Jul 26, 2020 at 10:33 AM Pablo Rath <pablo at parobalth.org> wrote:
> >
> > I am very sorry to inform everyone on this list that I had a severe power problem with my Micro Desktop 1.7.
> > I applied power to the DC Jack and the area right to the jack burned
> > out. (see attached picture).
> 
> thank you for sending this to the list, as i asked, after you sent it
> initially privately.  i had this happen to a 1.5 MD board 3 years ago,
> but no others, despite them running for prolonged periods of time.
> 
> what i noticed about that board was that the inductor was not properly
> soldered down.  this would be insufficient contact, introduce
> resistance, and at that point the RT8288 would go unstable.

Ok. As you have probably deduced from my questions I am not really into
hardware. Thank you for all your explanations and clarifications. 
I still try to wrap my head around what should work straight away, what
could work with the right modifications and what can never work...

[...]

> > As I said I am very sorry that I screwed up.
> > Luke, do you have any ideas what went wrong?
> 
> not in the slightest.  or - maybe: have a look at the contact points
> where the inductor sits on the PCB.  there should be quite a lot of
> solder, there.

Sorry for the dumb question but where can I find the inductor?

> > Do you think this
> > +also destroyed the computer card?
> 
> when it happened for me it did no damage.  all i did was (because i
> didn't have any spares) find a USB2 back-to-back power cable (i may
> have made one by cutting a plug off a USB device and wiring it to a
> 5.0v supply), plug it into one of the USB2 ports and provided "direct"
> 5.0v power that way.  you *need* a stable supply to do that (1.5
> preferably 2.0 A) designed *specifically* for providing USB power.
> UNDER NO CIRCUMSTANCES plug the 12v PSU into the USB socket.  and DO
> NOT use an "off-the-shelf generic 5.0v wall wart".  use something
> SPECIFICALLY designed for providing USB power because it is (a) stable
> and (b) current-limited.

I have a power supply from a Huawei Tablet (Output 5V, 2A) and one from
an old Ipad Mini (Output 5V, 1A) both with a wall plug and a female USB
socket. Can I use one of them with a standard USB 2.0 USB A to USB A (male to
male) cable?
The term 'back-to-back' power cable yielded limited search results in my
case. 
Another option is an official PSU for the Raspberry Pi, 5V, 2A with wall
plug and a non-detachable micro-usb cable. I can buy a micro-usb to USB
A adapter if this is going to work.
So I have to either buy a cable, an adapter or a whole new USB Power
supply depending on your opinion.

> if you plug the Card directly into a socket (OTG, removed from the
> MicroDesktop) - not via a USB hub - "ls" should show the familiar USB
> ID for the A20.

My initial thought today was: "NO, now everything is lost." so your
reply made my day. Tested the Card standalone and 'sunxi-fel version'
shows an Allwinner Device in FEL-Mode. Computer Card still alive!

Pablo