My lathe spindle came to an unusually abrupt halt a few weeks ago. Then had a buzzer alarm (having to do with the takisawa side of the electronics / the fanuc 6t didn't know what the alarm was, it just doesn't get the NC Ready signal). The lathe spindle motor was braking to stop the spindle before a tool change. During the braking it just slammed stopped, so fast that I believe you could hear the belts slip. A split second later / during this slamming brake, there was a pretty darn loud bang. I assumed something mechanical had happend. this wasn't the case. It turns out the 75A fuji ultra fast fuse had blown on the middle AC input leg on the spindle motor drive. The motor is DC / the drive is a thyristor DC drive. The fuse was the very loud bang.
So I ordered a fuse and installed it, I also replaced the MOV's as it appear that one of them might have been arced onto during the event. I got these things installed and fired up the machine. The spindle worked fine. great. Then I was varying the speed around a lot to try and stress the drive a bit. This was fine too, all the way up to max speed, and back down. However, during this varying I eventually rapidly put the speed control to minimum, so the motor had to brake hard. This resulted in the same thing - a very abrupt braking to zero speed, again so much so that the belts screeched a little. This time no bang though, and the fuse didn't blow.
Since the fuse didn't blow, now what? When I power on the machine, there is no alarm, but there is also no power applied to the motor drive. The status LED's on the front of the fuji drive just barely blink on for a split second and back out just as fast. Then nothing. The contactor that feeds the drive won't pull in. The fanuc just reports 'not ready' of course. I measured the fuses, none of them are blown. So maybe one of the SCR's actually got blown up? I don't know.
Has anyone ever had this happen on their Takisawa, or other lathe that uses a FUJI DC drive? Where the contactor won't pull in at all? / no error lamps are allowed to light because it just cuts power right away. I also measured the resistances between the inputs, outputs and GND - they're all > 500kOhm as the fuji drive manual says they should be. Apparently it is supposed to be shorted if an SCR is blown.