Laser "fades" out after a few minutes?

[telmnstr]

Quick question. We've rebuilt a Meistergram laser engraving machine that uses a synrad laser and Roland plotter guts.

A friend built a controller to PWM the laser that will soon be open sourced. Our timing is very very close.

At 50% or higher powers, the laser seems to fade out after about 15 minutes. After some time the laser seems to come back.

It's fan forced air, hardcore. The heatsink on the exterior isn't getting very warm.

Most of my experience is with argon & HeNe lasers.

The laser is from the 80s. There is concern that it is the tube age.

Any thoughts or experience that anyone can share?

[Tweakie]

First check the voltage and stability of your power supply to the tube.
Although it could be the gas in the tube my first thought would be with the RF units. Obviously a careful visual inspection may reveal something but I would initially replace the 1000pF silver mica capacitors and then give it a try. If no difference then replace the MRF150 or MRF151 RF transistors.

Hope this helps,

Tweakie.