Thanks for the information, when making measurements last week, I did it based on the information you posted.
I checked the board by connecting power from 3 different sources via usb:
- 2 different laptops with usb 3.0 ports
- power bank with regulator giving equal voltage 5v
- a separate power supply from a laboratory power supply
And connecting the power from the laboratory power supply using the JTAG FPGA pins you wrote about.
No attempt has produced positive results, Lime seems to be dead.
With USB plugged in:
Measuring the voltage on the resistors located at the top of the two voltage regulators (because they are smd elements and their pads are located below in contact with the PCB), on both of them I have obtained a measurement close to imput voltage, and testing the circuit for shorting with the multimeter did not detect anny broken circuit. Hence my assumption that the regulators are operational, because defective or burnt will give me a different voltage than the power supply at the input. I would like to ask you if I my assumption is correct?
With power on FPGA JTAG from voltage regulator:
Similar to above, almost no voltage on voltage regulators resistors.
Watching the whole thing under the magnifying glass I have not seen any damaged or scorched elements responsible for the power supply (resistors or regulators).
To sum up, the basic troubleshooting did not find the cause of the device’s failure (visual or related to the voltage fed) It looks like something is messed up with the voltage reulating circuit of the board. I am afraid that it requires more detailed inspection with more advanced equipment by the manufacturer.