Laser HV repair

I’m in the process of upgrading the brain in the laser from a cheap (and recently deceased) Chinese special to a new design based on the open source Lasersaur. More on that later.

I was right in the middle of testing my new design when the laser suddenly stopped firing. Apparently it was time for the HV supply to pack it in. The cause? A dead thermistor.

Can you spot the trouble?
Can you spot the trouble?

It looks like this one was being used to limit the inrush current at the bridge rectifier. Apparently it died a sudden and spectacular death.

I took a look around the shop and happened to find an old junked server supply with a very similar looking thermistor in it.

Could this part do the job?
Could this part do the job?

After finding the datasheets for the dead 5D-13 and the spare 15SP M005, it turned out that they were largely compatible.

5 Ohms at 25C is good enough for me.
5 Ohms at 25C is good enough for me.

So I swapped in the 15SP and fired up the supply.

The question is, do we have a charge?
But more importantly, did we get a charge?

Success! We have sparks. Now to reinstall it and resume robot brain surgery.

The real question is, why did it fail? I think some research into the switching frequency of the Lasersaur and the capability of this cheap supply are in order.