On Sun, Jul 26, 2020 at 10:33 AM Pablo Rath <[email protected]> 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. _______________________________________________ arm-netbook mailing list [email protected] http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to [email protected]
