gweike laser engraver lc1290 mirrors allign help

i got a new laser, LC1290 from gweike with 100w RECI, and i had to dismantle the top parts, not the rails, to be able to get the monster in the office.
now i have a biiiig problem aligning the mirrors. after many hours of forum reading, i think 3 mirrors are not on the same level.
so, i'm coming with some questions and begging for some experts help and reply's
1. is a must to center the beam on all 3 mirrors?
2. how can i check if all mirrors are on the same level?
3. is anyone have a tutorial to allign the mirrors from point of mounting, not just fine details?
4. at a surface of 1200x900, the dot can be set to hit the same place, on all the table surface, or it's just a myth? i can do that for the left half of table, but not for the right
thanks for reading and for possible answers

I think you could get better and faster help on Sawmillcreek in the engravers forum, lots of gweki owners there knowledgeable people

Hi Sanyyos
here's a video may help you check if the Laser mean on level and align the laser beam:
https://www.youtube.com/watch?v=pw8Ro2vEEzY
hope you can solve the problem soon.

thx a lot for the tutorial.
my problem is a little weird...
I have the dot in the same place on 3 corners: up left and right, down left, and in the 4th corner, right down, near the control buttons, my beam is always hiting 3 mm down compared with the others

Hi sanyyos

here is the video of the G.WEIKE machine aligned light path .
http://www.wklaser.com/vid_59.aspx

hope it is helpful.
thanks
Abby