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Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 1:32 pm
by mathieu
I connect the USB port on my pyboard D to a computer. Nothing lights up on the board; rshell is unable to see the board; no flash drive is mounted on the computer. Same results with a different computer, and with a different USB cable. Pressing USR and RST buttons to enter safe mode gets no response from the LEDs.
This may be a dumb question, but are there any other troubleshooting steps to attempt before I start to feel sad?
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 2:38 pm
by ThomasChr
What have you done to cause this?
The first step is to measure all relevant voltages. After that you can measure the clock input. A cpu with the right voltage on it‘s power pin and a clock should work...
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 2:39 pm
by dhylands
Try putting the board in DFU mode (ie connect the DFU pin to 3.3v) and press reset and see if the board shows up on DFU mode. Normally you'd see 3 LEDs on dimly.
If you can get into DFU mode you can reflash the firmware. Make sure you have the right firmware for three board. I.e pyb1.0 vs 1.1 vs lite as they have different frequency crystals.
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 2:55 pm
by ThomasChr
Do we talk about Pyboard or Pyboard D?
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 3:09 pm
by chuckbook
Note that there is a fuse in the USB-HS power path. If by any chance more than 1 A is drawn from the USB host, this would trip the fuse immediately. If a regular USB host port is used, the over current limit of a USB port will kick in at 500 mA leaving the PYBD fuse intact.
However, recent USB host ports can provide much higher currents and therefor the PYBD fuse will trip.
The state of the fuse can be check by measuring its resistance with a multimeter (make sure the PYBD is disconnected from any power source). Another method is to measure voltage on VIN while USB-HS is connected to an active USB host port. With an intact fuse it should read about 4.3 V +/- 5%.
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sat Apr 06, 2019 4:17 pm
by mathieu
A few answers:
- This is a pyboard D (PYBD-SF6-W4F2)
- I was (foolishly) driving a PAM-8403 audio amp out of the VIN pin of the WBUS-DIP68. I was under the impression that my computer USB could not deliver 1 A
.
- It does look like the fuse is blown (infinite resistance), and the LED lights up briefly if I power the board from VIN or from the outermost fuse connector (the tip of the fuse closest to VUSB)
If indeed this is a blown fuse, what are my best options to still be able to write code to the board and use the REPL?
Re: Unresponsive pyboard: how to tell if it's dead?
Posted: Sun Apr 07, 2019 10:15 am
by chuckbook
You can safely power a PYBD from VIN with a voltage from 3.3V to 4.8V. Don't use any voltage above 4.8V if your board has a wireless module installed. If you would like to power from a 5V power supply I recommend to use a 1A silicon diode in series with the 5V power line.