[j-nsp] How-to flash RE BIOS (U-Boot+loader) on bricked SRX650 SRE6

[Peter J. Cherny]

After a hang and power cycle during a "request system firmware upgrade 
re bios"
I have a SRE6 RE with no leds and no u-boot prompt.

Is this an RMA or does someone know the incantation required to re-flash 
the bios ?

BTW, it's not a h/w issue, the RE worked before, it's a classic bricked 
bios.
I suppose one failure in a dozen or so boxen is sort of ok, but not nice 
  <g>