On Sun, Jul 26, 2020 at 10:33 AM Pablo Rath pablo@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.
One thing that I noticed today was that UART worked when the card was powered up whilst attached to USB OTG alone (DC Jack on MD not connected)!
yes, i mentioned this already. the TX and RX line GPIO current is sufficient to "power" the LEDs and possibly the FT2322 IC as well.
But according to the wiki this should not work at all because of the Y6280 current control IC set at 1A acting as a diode in this case.
no: it's not being powered through the 5.0V rail: the LEDs on the USB-UART are being powered through the *processor*, through the TX and RX lines.
When I applied power only to the MD I noticed that UART output was complete garbage (random characters).
yes. i did say. you get GND loops that spike the USB-UART sufficiently to trigger the RX line.
I don't know if only sometimes or everytime. When on DC power, board in FEL-mode with no card and pressing '2', then connecting USB OTG and booting U-Boot sunxi over FEL everything worked flawlessly.
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.
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.
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.
If the error is on my side (embarassing but still the better +case) I will have to swallow the bitter pill that I screwed up badly. I am still going to cover the costs of computer card and MD so there will not be a financial loss to the project.
appreciated
I am very disappointed as I have made could progress. Had sunxi U-Boot, sunxi 3.4.104 kernel running and booting Debian Stretch rootfs...
great!
On the other hand if this is a general problem better we know it now and can take the necessary steps.
modifying the 1.7 MD PCB and going through *yet another* round of PCB development costs and time delays - this not something i want everyone to have to go through. particularly because they're already manufactured.
sigh.
l.