The invention is drawn to a test circuit for an ink jet printer which measures the voltage decay over time. The tensioner may comprise a base, a resilient device, and first and second arms pivotally coupled for movement in an open and a closed direction. For other embodiments, a conductive trace layer coupled to the input of each cross-coupled inverter includes a high-resistivity portion that provides the SEU-hardening series resistance. Each optically sensitive layer is interposed between two electrodes. The jet pump may include a power fluid intake configured to receive a power fluid and a produced fluid intake configured to receive a produced fluid. A brush member located on the carrier disc at a position corresponding to the inner data track of a music CD disc is provided for engaging a lens and a peripheral portion of a lens carrier of the head when the head is in the inactive position for protecting the lens and the peripheral portion against dirt and dust.