You are right, that is a uboot screen
Why it won't boot from SD seems very strange, if there is no uboot at all no led will turn on,
but since you have tried a few images on SD this can't be right
(nearly always an image also has a uboot in 1st 16M)
Try mrfixit image, that has a BSP style uboot
If it doesn't work on SD (with emmc out), try it on emmc
------
Since you know old emmc has an OK uboot copy the 1st 16M to say usb stick
(dd if=/dev/emmc of=/mnt/usb/1st-16 bs=1M count=16)
Then, with new emmc in adapter copy mbr (1st sector,,count=1 bs=512) somewhere
write 1st-16 (from usb) to new emmc, then saved mbr.. Then new emmc should boot
Also,, there are, not so expensive, usb ->ethernet dongles.. usb2 =<$10, usb3 =$15-25
On occasion quite usefull
Why it won't boot from SD seems very strange, if there is no uboot at all no led will turn on,
but since you have tried a few images on SD this can't be right
(nearly always an image also has a uboot in 1st 16M)
Try mrfixit image, that has a BSP style uboot
If it doesn't work on SD (with emmc out), try it on emmc
------
Since you know old emmc has an OK uboot copy the 1st 16M to say usb stick
(dd if=/dev/emmc of=/mnt/usb/1st-16 bs=1M count=16)
Then, with new emmc in adapter copy mbr (1st sector,,count=1 bs=512) somewhere
write 1st-16 (from usb) to new emmc, then saved mbr.. Then new emmc should boot
Also,, there are, not so expensive, usb ->ethernet dongles.. usb2 =<$10, usb3 =$15-25
On occasion quite usefull
