We have an 60W Chinese laser engraver, that has been working successfully for about year. In recent times the power output has been dropping, meaning it needs a higher power setting to achieve the same results. Now, when starting from cold at full power, when continuously engraving a straight line, the output will quickly reduce over course of about 30-60 secs until it doesn't mark the material at all.

Things I've checked:
- Consistent purple illumination in the tube
- Mirror alignment appears to be OK
- Constant 25mA through laser tube, even as engraving depth/intensity decreases

Have noticed the engraving point on the material does seem to flicker more than it used to, suggesting output isn't stable

Can anyone provide some suggestions of possible causes, and/or further tests I could do? Could it be the laser tube is dead or nearly dead? Or cooling not adequate? Nothing has changed on the cooling side, as far as i can tell the water flow is as high as it ever was.

Thanks for your help