Cold Probe Preamp Testing

Cryo-driver DC condition:

1.       Put system into tune mode.

2.       Remove cable from pre amp input J5331, and install a BNC “T” in place.

3.       Connect one end of “T” to voltmeter to measure Voltage, leave other end of “T” open. Measure voltage at J5331 (voltage should = 5.0V +/- .1V).

4.       Connect 50 ohm load on “T”, measure voltage, (voltage should = ~1.65V)

Internal Pre-amp DC condition:

1.       Put system into tune mode.

2.       Remove 50 ohm from “T” and install preamp cable P5331.

3.       Measured voltage should now be between 2.50-3.0V (limits 2.25-3.25) with preamp at room temp or between 2.75-3.25V(limits 2.5-3.5) with preamp at operating temperature (25K).

Note: Preamp voltages outside the limits will require factory repair.

Pre-amp Diode test:

1. Use a DVM set to the “diode test” Mode

2. Place the positive meter lead on the center conductor of the H1 transmit port, of the cold probe, and the negative meter lead on the shield portion of the connector

3. Verify the following voltages:

·         Approximately 1.3 VDC when warm (room temperature)

·         Approximately 1.9 VDC when at operating temperature (25 degrees Kelvin)

Pre-amp impedance test:

1. Use a DVM set to the “resistance measurement” mode

2. Measure the impedance at the H1 transmit port of the cold probe

·         You should read approximately 5 to 20 Mega Ohms

3. Measure the impedance at the H1 receive port of the cold probe

·         You should read approximately 30 to 40 Ohms