Try this (because I am guessing you also did a uboot update, manjaro's uboot are not so good)
Take off back, remove/disable emmc, put KNOWN good uSD in,
do resets in order (testing after each),,, hard pwr-off (7s press pwr button),, hard reset (20+s), internal reset button
If necessary, do this twice
Take off back, remove/disable emmc, put KNOWN good uSD in,
do resets in order (testing after each),,, hard pwr-off (7s press pwr button),, hard reset (20+s), internal reset button
If necessary, do this twice