A9 Input Attenuator

1.Perform the Input Attenuator Accuracy test in Chapter 3 of the Installation and Verification Manual.

2.If there is a step-to-step error of approximately 10 dB or more, continue with step 3.

3.On the HP 8560A press [n), and ATTEN AUTO MAN until HAN is underlined.

4.Step the RF ATTEN from 0 dB to 70 dB. A “click” should be heard at each step. The absence of a click indicates faulty attenuator drive circuitry.

5.Monitor the pins of A14U420 with a logic probe or DVM while setting ATTEN to the values listed in Table 11-3.

Note

The logic levels listed in Table 11-3 show the default AC usage (Pin 5 low, Pin

 

6 high). DC usage (Pin 5 high, Pin 6 low) is not shown.

 

 

6.If one or more logic levels listed in Table 11-3 is incorrect, disconnect Wll from A14J6 and repeat step 4 checking only pins 3, 5, 11, and 13 of A14U420. Pins 4, 6, 10, and 12 should all read low TTL levels.

7.If one or more logic levels listed in Table 11-3 is incorrect with Wll disconnected, troubleshoot the Al4 Frequency Control assembly.

8.If all logic levels are correct, the A9 Input Attenuator is probably defective.

Table 1 l-3. Attenuator Pin Values

 

 

 

 

A14U420

Pin Number

 

 

 

 

 

-

 

 

 

 

 

ATTEN Setting

3

4

5

6

10

11

12

13

(dB)

20 dB

20 dB

 

DC

A C

4 0 d B

40dB 10 dB

10 dB

 

 

 

 

-

 

 

 

 

 

0high low low high low high low high

10high low low high low high high low

20low high low high low high low high

30low high low high low high high low

40

high

low

low

high

high

low

low

high

50

high

low

low

high

high

low

high

low

60

low

high

low

high

high

low

low

high

70low high low high high low high low

-

RF Section 11-7