Diagnosing faulty eMMCs?

[Trash_Can_Man]

Hi,

I received a couple of months ago two ROCK64 4GBs as well as two 64GB eMMC modules. Yesterday, I finally began trying to get them up and running. I'm planning to run my home automation and NAS on them, so I'd be getting Armbian Stretch on them. I failed to order the eMMC USB adapters (mistake!), so getting the eMMCs flashed were a bit problematic. I finally did the following:

I installed these prerequisites:

https://github.com/ayufan-rock64/flash-tools

https://github.com/ayufan-rock64/rkdeveloptool

Next, I got myself a USB A-A cable (actually had an USB B-B adapter which worked well with a couple of USB A-B cables - the other alternative would've been to splice two USB cables).

Then, went through the following process:

1. Placed a jumper on the maskrom headers (the ones closest to the Recovery button)
   
2. Connected the USB cable to the upper (OTG) USB port
   
3. Connected the power cable
   
4. After a few seconds, removed the jumper
   

Then, I used the `rklinux_flash` script to flash an image:

Code:

sudo ./rklinux_flash Armbian_5.42_Rock64_Debian_stretch_default_4.4.124_desktop.img

This approach produced a bootable device.
Now, the question: this only seems to work on one of the eMMC modules. With both of them, flashing completes just fine. However, only one of the devices boot and become accessible (both via local console and SSH). With the other one, there's no HDMI output and the green Ethernet light keeps flashing suspiciously.
Both of the SBCs seem to be fine. Both of them boot and work with the good eMMC and give the same behaviour with the bad one, so I think the issue is with the eMMC module.
Now, how should I debug the issue further? Are the symptoms enough for me to request a replacement eMMC from PINE64? I already ordered the eMMC adapter but it'll probably take a couple of weeks to arrive. Could I get any additional information on the serial console? I have a bunch of ESP8266 related hardware which I could probably use to jury rig a 3.3V serial port adapter, but that's some trouble I'd prefer to avoid.
Thanks for any help!

For a start id suggest burning an image on the ""faulty"" one with a different flasher, as example i usually use etcher with exelent results...but im not sure if you have either an usb-emmc or microsd-emmc adapter...
nvm that, now i see that you dont have the adapter...tho somehow if its a new emmc module it still ""feels"" like the mbr or however is called nowadays to the very few sectors on a storage device is not correct...