BLE Mesh light swtich example works fine but can't connect to the boards via SES afterwards.

[kenjiume]

Hi,

I tested to run BLE Mesh(v1.0.1) light switch example using SEGGER embedded studio(SES) on Windows10
and three nRF52DK(ntf52832) boards .. one client, two servers.
It worked fine!

But, after that, all three boards couldn't connect to SES via J-Link.
I think, an update dialog of J-Link driver shown on SES just after connecting boards on USB
and I updated it.

In this forum, I found the comment that restarting a board as Bootloader mode and then,
copying J-Link OB-xxx.bin file to a top of a folder mounted as "BOOTLOADER".
It works for one board (client). but about other two boards (servers), they can't even be mounted on Windows10 so I can't copy the fle.

nrfjproj and JLink.exe just printed "ERROR: There is no debugger conected to the PC",
"No emulators connected via USB".

How can I restore the boards?  Some external devices need?
I'm a beginner around HW development so any clues to solve this problem will be helpful.

Thanks

[kenjiume]

solved.

I don't know why but USB cables for two boards were both dead at the same time.
USB's power supply line was no problem but data line was completly dead.... surprising.
an updated driver was not a problem about this issue.