The people using the machine a the hospital would replace the (expensive) fuses when they blew. It was the manufacturer that made the later model (the Therac-25

The people using the machine a the hospital would replace the (expensive) fuses when they blew. It was the manufacturer that made the later model (the Therac-25) that didn't have the fuses (and other "old" hardware features). Obviously, something was still very wrong. User error (or other bugs? I'm not sure) in the older hardware and the infamous race condition in the software-controlled Therac-25 was causing the beam to turn on some shockingly high amount of power. The better design of the older models saved people's lives by simply blowing fuses when the power went too high. You could, perhaps, blame the poor communication between the hospitals and the manufacturer, because the fuse problem should have cause a bit of a panic among the engineer who designed the machine.