I think I may have killed my Pico as I can no longer connect to it.
After soldering the ESP8266 onto it with the shim my PC could no longer find the Pico com port and couldn't tell if the red LED was lighting up when plugged in. I removed the ESP8266 but not the Shim and plugged in back in. Again I couldn't find its com port to connect it. I've also tried on another PC and exact same result.
When I plug it in the red LED lights up but very dim. If I plug it in while holding the reset button I get the same result, red LED dimly lit.
I'm worried I may have had a solder short when I first plug it in but can't tell. I used my multimeter's continuity function to check but I have since removed the ESP8266.
What should I do next to debug the problem?
Argh, sorry to hear that - it sounds like at some point GND and 5V have got shorted out (maybe those 3 0.05" pins that connect to the board?). It's worth checking they're not still shorted...
It's not the end of the world - it's almost certainly meant that the diode on the Pico that transfers USB power to it has blown up. It's the black 2 legged device with S4 written on it nearest the USB connector. It might even look a bit misshapen/singed.
To test, you could do one of:
.. then plug it into USB and it should start working again.
Hope that helps!
Just to add - if you short out the diode, you can't then use an external power source with the Pico - you'll always have to power it via USB. It might be that's good enough for you though.
I first checked everything again for shorts, but found nothing. I then shorted out the diode and it works! As you said I can only use it via USB but for now I think that is all I'll be using it for.
Would a permanent fix be to replace the diode?
Yes, absolutely! I'm using the PMEG3005AEA on the rev 1v4 boards, which is a bit better.
Link from Farnell is: http://uk.farnell.com/nxp/pmeg3005aea/diode-schottky-sod-323/dp/8737975
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