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MP motor runaway

The MP diplexer gave more serious worries. Due to the poor design and scarce documentation of the stepper motor controller chip that is part of the hardware used to move the MP mirror, the moving stage ignored and destroyed a limit switch, which, indirectly (details spared to the general reader) caused a jump of 2.000 mm in the encoder origin. Fortunately, the on-site receiver engineer found a short-term workaround. Subsequently, within 48 hours, and through close cooperation between the 30-m staff and the Grenoble receiver and computer groups, the problem was solved and fully diagnosed (in that order). Future MP diplexers will have improved hard- and software to circumvent the controller chip problem.