No, my bet (particularly for the LOCK signal) for the output signals is open collector. If you don't see any action, try them with a light pull-up to 5V. Most rubidiums are good for at least 24-30V on their O.C. outputs. ----------------- On the monitor outputs, fire the unit up and watch them with a voltmeter. They are likely either DC levels or 0-5V CMOS outputs.