Interesting explosion inside 2018-RM Laser power supply:
The UV Laser in our mass-spectrometer department had a strange failure:
blown supply fuses, and a huge splotch of golden mirror coating on the PCB connected to all the large power components. There was a direct short across the main power line on the DC side. The point of contact was explosively vaporised, coating everything around it with metallic copper.
The failure apparently came from a MOV device which had been crushed between two circuit boards, where a big screw with DC main power had pushed through the epoxy coating on the MOV. This placed a short on the output of the main 3-phase bridge rectifier, which blew out one of its diodes before the 50-amp cartridge fuses blew.
I found that Spectra Physics sells a repair kit associated with such failures: the bridge module plus cables and shorter screws. Also, the
50-amp cartridge fuses can be had from Mouser. (and if Spectra Physicsshould discontinue their kit, the three-phase bridge is similar to a known part available elsewhere):
Bridge Rectifier Upgrade Kit, 4801-1108UPG, Spectra Physics Bridge Rectifier, 3-phase, EH100 Microsemi.com
After replacing the bridge, the laser still didn't work: it ran at full power (50 amps,) and the current-adjust pot on the remote console box had no effect. Occasionally it went into overcurrent shutdown. I traced this to a shorted zener. Besides killing the bridge module, the transient had shorted out CR-23 on the logic/driver board, a 1N4735
6.2V zener associated with the transistor driving the base pin on one of the big darlingtons in series with the main 50amps.One last note. I had one of the big darlingtons removed from the water-cooling heat sink and noticed that the heat sink has large holes allowing direct water contact with the bottom plates of the transistor bricks. If you should try removing one of the bricks while the cooling
pump is running, you might get a big wet suprise!
((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph206-543-6195 http//staff.washington.edu/wbeaty/