Agilent Technologies 856290216 service manual Unlocked Reference PLL, Operation, Troubleshooting

4.Confirm proper power levels for the signals at the input to the “N” dividers (4), the reference inputs (5 and 7), and the loop feedback path (6).

Unlocked Reference PLL

Operation

The 600 MHz reference is generated by tripling, then doubling the output of the 100 MHz phase-locked loop. If the 600 MHz reference is off frequency, the 100 MHz phase-lock circuitry is probably at fault. If there is no signal present at A15J701, or if the level is less than

-3 dBm, the 100 MHz VCXO, the tripler, or the doubler circuitry has probably failed. Refer to function blocks Q, R, and S of the Al5 RF schematic (08563-90071, 08563-90072, or 08563-90073) sheet 2 of 4 in the HP 8560 E-Series Spectrum Analyzer Component Level Information binder.

Troubleshooting

Check 100 MHz VCXO, tripler, and doubler (steps 1-7)

1.Using an active probe/spectrum analyzer combination, such as the HP 85024A/HP 8566B, measure the tripler output at A15TP700. The tripler output should be +3 dBm f2 dB.

2.If the tripler output is within tolerance, suspect the doubler circuitry. Refer to function block S of the Al5 RF schematic.

3.If the tripler output is too low, probe the output of A15U700 RF amplifier. The level should be i-16.5 dBm f2 dB. The level at the input of A15U700 should be i-8.5 dBm f2 dB.

4.If the level at the input of A15U700 is too low, suspect a faulty 100 MHz VCXO. Refer to function block Q of the Al5 RF schematic.

5.On the spectrum analyzer, press [CTRL), REAR PANEL , and 10 MEz INT .

6.Measuring the tune voltage indicates if the 100 MHz PLL is locked. Connect the ground lead the voltmeter to A15Jl pin 3 and measure the voltage at A15J700 pin 3.

7.The tune voltage should be between +l and +24 Volts. If the tune voltage is incorrect, place the P700 jumper (on A15J700) in the TEST position (pin 1 to pin 2). This sets the tune voltage for varactor A15CR700 to the nominal +13 Volts, making it easier to troubleshoot the 100 MHz VCXO, tripler, and doubler. Remember to return P700 jumper to the NORMAL position when you have finished troubleshooting the oscillator circuitry.

8.If the 100 MHz oscillator is working, the reason for the unlocked condition is either a problem in the 10 MHz reference or a fault in the signal path around the loop.

1 l-1 6 Synthesizer Section