I have one of your DS7A stimulators, but the pulse duration control knob doesn’t turn to the 0.5-2ms settings, should I return it for repair?

The higher output DS7AH has a limiting feature that for safety reasons prevents use of these wider pulse durations. Although your stimulator has DS7A on the front panel, please check the serial number label on the back of the unit, as I think you will find it indicates that it is a DS7AH.