29.If the front-panel CAL OUTPUT amplitude is out of specification and cannot be brought within specification by adjusting A15R561, CAL AMPTD, check the Calibrator AGC Amplifier with the following steps. Refer to function block W of Al5 RF Schematic (sheet 3 of 4).

Note

The 300 MHz CAL OUTPUT signal comes from the divided down 600 MHz

 

which is passed through a leveling loop. The 300 MHz signal passes through

 

a low-pass filter for reducing higher harmonics. These harmonics can fool the

 

detector. The 300 MHz signal passes through a variable attenuator controlled

 

by PIN diode CR503 which is controlled by the feedback loop. Diode CR504

 

is the detector diode (the same type as CR505). Diode CR504 provides

 

temperature compensation between the reference voltage and the detected RF

 

voltage.

 

 

a. Measure the level of 300 MHz at Al5 TP505 with an active probe/spectrum analyzer combination. If the signal is less than +2 dBm, be sure to perform the beginning steps of this procedure.

b. If the signal at this point is correct, place a short across the PIN diode CR503.

c. If the signal level at the CAL OUTPUT is still less than -10 dBm with CR503 shorted out, troubleshoot the RF forward path through amplifier Q505.

d. If the CAL OUTPUT signal level is greater than -10 dBm, troubleshoot the PIN diode attenuator, the detector, or the feedback path.

30.Measure the detector voltage at A15J502 pin 14. The voltage should measure approximately +0.3 Vdc when the CAL OUTPUT signal is at -10 dBm. This voltage should change with adjustment of A15R561, CAL AMPTD.

31.Check that the voltage at U507A Pin 3 is +1.7 Vdc. If this voltage is not correct, there may be a problem with the +lO V reference.

32.Measure voltage at U507B pin 5 while adjusting R561. This is the temperature- compensated adjustable voltage reference to which the detected voltage is compared. It should vary between +1.3 V and -0.6 V.

33.Adjust R561 to its limits and verify that the output U507B pin 7 measures approximately +9 Vdc at one limit and -12 Vdc at the other limit.

Third LO Driver Amplifier

The Third LO Driver Amplifier (Q503) amplifies the 300 MHz from the 600 MHz phase-lock loop to a sufficient level to drive the LO port of the Double Balanced Mixer. During the SIG ID operation, diodes CR501 and CR502 turn off the 3rd LO Driver Amplifier in order to minimize the amount of 300 MHz going to the double-balanced mixer.

1.Press (AUXS), INTERNAL MIXER ,and SIG ID OFF.

2.Use an active-probe/spectrum-analyzer combination to confirm the power level of the 300 MHz signal at the following test points:

A15TP602

>+7 dBm

A15TP504

>+15 dBm

lo-44 Synthesizer Section