I picked up a Rofin CO2 laser condition unknown today. Its a 300W unit that has a head and a separate power supply. the head is connected to the power supply with a big 7/16 style RF cable and a DB25 for signals and control. Looking at the manual I saw that the power supply is composed of three individual 48v power supplies which are in series so thinking I could rewire it to run off single phase, just parallel the power supplies.
So I took off the back cover when the smell hit me in the face, a strong chlorine smell. And then I noticed that the insides where covered with a brown stain. NOT GOOD
IMG_1583 by
Jerry Biehler, on Flickr
I disconnected the in and out leads and slid the power supply out. Top cover has more of the staining so ti was definite coming from there. I popped off the cover to find this:
IMG_1589 by
Jerry Biehler, on Flickr
IMG_1587 by
Jerry Biehler, on Flickr
One of the output inductors is totally fried. So two things I notice, one, it is not three individual power supply like the manual shows, it is one giant 48v power supply with rep output transformers with he primaries in series and the secondaries in parallel after rectification. All driven by a mosfet h-bridge. The mosfet drive board can be seen at the top center above with the fan which has seen better days. Second thing is that other than the smoke the damage is limited to the output inductor, the hall current sensor, and the fan.
But why only one inductor fry? The transformers are in series so if one dies they both will die so the load can't become uneven that way, if the RF power supply had an issue the whole unit should have faulted out since the current sensor is on the output. I pulled the buss bar off the output of the diodes and checked them and they are all fine and also the transformers which appear to be fine, I need to grab my 34401A with the kelvin clips to check them out for sure, it is too low to measure with my hand held. Maybe a bad connection on the inductor cause a runaway heating event and just killed it?
I think its repairable, The ferrite itself won't care about the heat, I can rewind it with suitable wire and make it match the existing one with my old LCR meter. The current sensor turns out to be a Chinese knockoff of a LEM125-P which is about $30. And the little fan is a generic 12v 40mm fan, I probably have one of those lying around someplace.
So first thing I am going to try and clean off some of the boards, the mosfet driver is the worst since it just sucked the smoke through. Get that back together and then check out the current sensor, easy enough to test, I need to get a new connector for the ribbon cable, it melted.
A couple more pics of the carnage, the first one is the inside of the top cover, you can see how the little fan circulated the smoke.
IMG_1597 by
Jerry Biehler, on Flickr
Current sensor:
IMG_1594 by
Jerry Biehler, on Flickr
Mosfet h-bridge board.
IMG_1599 by
Jerry Biehler, on Flickr
This thing smells sooo bad.