Fluke 5720A service manual 3905 A6 Phase Lock Loop At 10MHz, 3906 A6 Phase Lock Loop At 30MHz

Troubleshooting 5

Interpreting Diagnostic Fault Codes

3905 A6: Phase Lock Loop At 10MHz

The Wideband assemblies are configured to 3.5V at 1.3 MHz, 1.2V at 1.3 MHz, 2.0V at

3.0MHz, 1.0V at 4.1 MHz, 3.3V at 5.0 MHz, 2.0V at 6.0 MHz, 2.0V at 7.0 MHz, and 2.0V at 7.9 MHz. The input voltage to the VCO circuit on the Wideband Oscillator assembly is resistively divided creating WB PLL DIAGNOSTICS which is routed to the Wideband Output assembly where it is connected to the SDL line for measurement by the adc circuit on the DAC assembly. This fault occurs if the input voltage to the VCO is not within 25% ±0.75V of the expected value. A failure indicates the Wideband Oscillator (A6) assembly is probably at fault.

3906 A6: Phase Lock Loop At 30MHz

The Wideband assemblies are configured to 3.5V at 30.0 MHz and 1.2V at 30.0 MHz. The input voltage to the VCO circuit on the Wideband Oscillator assembly is resistively divided creating WB PLL DIAGNOSTICS which is routed to the Wideband Output assembly where it is connected to the SDL line for measurement by the adc circuit on the DAC assembly. This fault occurs if the input voltage to the VCO is not within 25% ±0.75V of the expected value. A failure indicates the Wideband Oscillator (A6) assembly is probably at fault.

3907 A5: Rms Sensor At 10MHz

The Wideband assemblies are configured to 3.5V at 1.3 MHz, 1.2V at 1.3 MHz, 2.0V at

3.0MHz, 1.0V at 4.1 MHz, 3.3V at 5.0 MHz, 2.0V at 6.0 MHz, 2.0V at 7.0 MHz, and 2.0V at 7.9 MHz. SENSOR CAL which is the output from the RMS Sensor and Amplitude Control circuit on the Wideband Output assembly is connected to the SDL line for measurement by the adc circuit on the DAC assembly. This fault occurs if RMS Sensor output is not within 15% of the expected value. A failure indicates the Wideband Output (A5) assembly is probably at fault.

3908 A5: Rms Sensor At 30MHz

The Wideband assemblies are configured to 3.5V at 30.0 MHz and 1.2V at 30.0 MHz. SENSOR CAL which is he output from the RMS Sensor and Amplitude Control circuit on the Wideband Output assembly is connected to the SDL line for measurement by the adc circuit on the DAC assembly. This fault occurs if RMS Sensor output is not within 15% of the expected value. A failure indicates the Wideband Output (A5) assembly is probably at fault.

3909 A5: Rms Sensor At 6.5V DC In

The 6.5V reference (BRF6, BSRF6) is connected to the input of the RMS Sensor circuit on the Wideband Output assembly. The nominal 6.5V output of the Sensor is divided and buffered before being measured via the SENSOR CAL line. SENSOR CAL is connected to the SDL line for measurement by the adc circuit on the DAC assembly. This fault occurs if the output of the Sensor is not 6.5V ±0.47V. A failure indicates the Wideband Output (A5) assembly is probably at fault.

3910 A5/A6: Ampl. Control At 10MHz

The Wideband assemblies are configured for a 3.5V and 1.2V output at 1.3 MHz. WB AMPLITUDE CONTROL which is the control signal to the Wideband Oscillator assembly is divided and connected to the SDL line for measurement by the adc circuit on the DAC assembly. At the 3.5V level it is checked to be 4.5V ±1.0V and at the 1.2V

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