If you are certain that is exactly what happened, then the most likely thing is that you have blown up the diode D1 which connects Vbus to Vsys.
A second possibility is having damaged tracks.
You could test this with a voltmeter: while the board is connected to a USB power source, Vbus should measure about 5V, and Vsys should measure about 0.4V less than Vbus. If Vsys is much less than Vbus (say 1V or more difference) the there's a problem in that area. You could also measure the two ends of the diode itself, which should give you exactly the same voltages as you are measuring on the pins (Vbus on one end and Vsys on the other), with any difference suggesting perhaps vapourised tracks (which you should be able to spot visually with a bright light and a magnifier).
This 'almost working' behaviour is a bit odd, but my guess is that the fault has left D1 (or the tracks) only conducting slightly - providing enough power to run the bootrom and show the USB device, but not enough to program the flash or to boot from the flash and run at full speed (both of which require more power than just running the bootrom USB).
If my guess is correct, then you could 'fix' it by wiring a link between Vbus and Vsys - that obviously stops you using Vsys as an alternative power input, but should give you a working USB-only PicoW.
A second possibility is having damaged tracks.
You could test this with a voltmeter: while the board is connected to a USB power source, Vbus should measure about 5V, and Vsys should measure about 0.4V less than Vbus. If Vsys is much less than Vbus (say 1V or more difference) the there's a problem in that area. You could also measure the two ends of the diode itself, which should give you exactly the same voltages as you are measuring on the pins (Vbus on one end and Vsys on the other), with any difference suggesting perhaps vapourised tracks (which you should be able to spot visually with a bright light and a magnifier).
This 'almost working' behaviour is a bit odd, but my guess is that the fault has left D1 (or the tracks) only conducting slightly - providing enough power to run the bootrom and show the USB device, but not enough to program the flash or to boot from the flash and run at full speed (both of which require more power than just running the bootrom USB).
If my guess is correct, then you could 'fix' it by wiring a link between Vbus and Vsys - that obviously stops you using Vsys as an alternative power input, but should give you a working USB-only PicoW.
Statistics: Posted by arg001 — Tue Dec 03, 2024 11:02 pm