PinePhone Beta Edition will not boot from MicroSD card

[spazz]

If an SD card has previously had an OS flashed to it you need to zero out the first few bytes or it will cause the device to not boot to emmc.

Hi @MtnSk8 (and anybody else). 
I'm having exactly the same problem as the OP. 
Brand new SD card. 
I have a Pinephone Convergence Beta edition. 
Running lsblk on the phone, it actually sees the sd card. 

However, no matter what I seem to try, I cannot boot it to either PostmarketOS as flashed to the SD card, or to Jumpdrive (developed by some of the Postmarket developers). 

This may be a dummie question, but, in reference to your answer: 
HOW do I zero "the first few bytes" of the SD card, 
and exactly how many is the first few? 
1?  2? 8? 16? 512? 1024? 

I took a gamble on this from pinephone documentation 
https://wiki.pine64.org/index.php/PinePh...structions

and tried: 

Code:

sudo dd if=/dev/zero of=/dev/[DEVICE] bs=8k seek=1 count=4

But have no idea if that's what you mean. 
Anyway, it didn't help. 

I am flashing using standard dd method  (having first run unxz to decompress the postmarket.img.xz file) 

Code:

sudo dd if=postmarket.img of=/dev/sdXX status=progress

and also trying to flash using the interesting postmarket.img.xz  piped through dd as described in postmarket documentation 
https://wiki.postmarketos.org/wiki/JumpDrive

Code:

xz --decompress --stdout pine64-pinephone.img.xz | sudo dd of=/dev/mmcblk... status=progress

In this case, I think the instructions are indicating doing this on the pinephone itself, but I am flashing it to the SD card using my linux desktop, 
so 
    /dev/mmcblk... 
becomes 
    /dev/sdXX 

Thanks anybody for any help or advice