Downloading Bootloader Fails

I have several RockPi 4C boards that now fail to do anything. They will not boot. No flashing blue LED.

So I have attached them in mask ROM mode and see them:

$ rkdeveloptool ld
DevNo=1 Vid=0x2207,Pid=0x330c,LocationID=403 Maskrom

But when I try to do anything with the device, I get nothing:
$ sudo rkdeveloptool db rk3399_loader_spinor_v1.15.114.bin
Downloading bootloader…

and it just hangs.

Also:

$sudo rkdeveloptool wl 0 zero.img
Write LBA failed!

Does this mean I have bricked/dead boards? I’ve checked the power supplies and they look good. But anything else to check?

I’d love to get these boards booting, again!

Thank you!