Many thanks for your reply. Yes I've read this thread, I use 2 methods :
1- from the windows console :
esptool -vv -cd nodemcu -cb 921600 -cp COM3 -ca 0x0 -cz 0x400000 -ca 0x00000 -cf DA2000-V6-6digit.bin
2- from ESPEasyFlasher
Each time the transfer looks good. And in fact the wemos well starts, as it can display the message SPIFF5 before counting from 0 to 9 infinitely. It can keep past wifi setup, and the IP address is seen on the network, therefor I cannot connect to the wemos.
Are you sure that SPIFF5 message is really an error? Mine displays that message during a normal start-up. It goes: STArT_ SPIFF5 nEt_UP ntP_UP and then rtC_UP (I think, that last one is real fast).
If the clock is not yet set up on the network, instead of nEt_UP you get an error and one tube is back-lit with blue. That means the Wenms is being an access point (not a station) and you have to connect to it and give it the credentials for your WiFi. See page 14 of the user manual.
The user manual says the clock's SSID is "ESPClock" but I think it is actually "VFDClock", It should be easy enough to figure out since it's likely the only network that will show up with Clock in its name!
Look into it later when the dust is clearing off the crater.