WOOHOO!!! I did it! QB board up and running ...
I'm one of us!!! haha
I undid the socket screws on the board, but it turns out that's unnecessary - the base of the board is plain and flat, no solder to access.
So I tried to de-solder the Molex connector from the top, but it wouldn't budge, it seems there's a decent amount of solder underneath it, not just either side. However I had already broken the top part off it earlier (the ~2mm x 4mm lever part) ... so inside you can see two 'gates' diagonally closed toward each other like
/ \, which opens up a bit as you push the exposed wire tip through
/|\, but I could see a lot of solder inside too. Anyway by keeping the soldering tip near the gates and pushing the wire in at the same time, eventually it freed up and she went through normally... phew!!
So i believe the reason I couldn't use this particular Molex connector is some excess solder had fixed one or both of the gates in place. Then a bit of solder on top for extra peace of mind / justice. Problem solved, though it'd be nice if i didn't have to break the top lever off the connector, but I can't see a way to de-solder it seeing as it's seemingly soldered on its base.
Then I grabbed a fire blanket and put some safety glasses on haha, and plugged the power in ... nothing exploded and I wasn't electrocuted which felt surreal haha, and then WHOA!! so bright! Success!!! I unplugged it pretty much straight away then, as that was the 6500k veg board which i don't really need at the moment ... anyway now to try the same fix on the 3000k flower board so I can start using it tonight!
THANKYOU everyone who's contributed to this
freakin awesome thread and especially those who've been patient and generous with their expertise and personally helped me and some of the other electronics newbies, it's super exciting to step up to this new level of efficiency thanks to the Sammy LM561C's - hey we've all gotta do our part for the environment