Keithley 160/Repairs

All ranges broken

If all ranges on your instrument are broken, but the power supply is fine, it check the analog output on the rear of the instrument. It is directly connected to the output of QA703 (an LM201 op-amp). Since the analog output connector is a open two-prong type it is very susceptible to accidental shorting. After replacing the op-amp, my instrument came back to life. I added a 1 kΩ resistor in series with the external output connector, to prevent accidental shorts to destroy the op-amp in the future, while still allowing this point to be accessible for calibration.