Mirrors adjusted - but beam isnt a complete circle?

I have adjusted the mirrors on my 80w red and black Chinese laser, the dot is roughly in the center of the third mirror. But when trying to adjust the lens vertically, I can see that the mark left when moving the table 100mm down is far from a circle. It almost looks as if something is shadowing for the beam. I have already removed the air assist nozzle…
Any input or help appreciated


Hi and welcome to the forum. Normally the beam coming out of the laser should be a solid circle. Do you get the same shape on the first mirror? If you do, it may indicate that your tube is failing and it is entering a different TEM mode.

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