Abstract: A surface readout (SRO) system for use with a wire line drill stem testing apparatus is disclosed. More particularly, the preferred and illustrated embodiment sets forth control circuitry for such a system. At the time that a well has been drilled and a potentially productive formation has been located, test apparatus incorporating a probe assembly is lowered on a wire line. The probe assembly incorporates a latch mechanism and a motorized tester valve opening apparatus. This disclosure sets forth a control system for the latch to fasten the probe in the downhole apparatus for conducting pressure and temperature testing of the formation to determine its flow and production potential. Moreover, a motor control circuit is also included to open the tester valve. These devices are located in the probe and are triggered into operation by signals transmitted on the wire line to the probe.