Table 7-9. Logic Levels at A3U108

i

-

 

 

 

 

 

 

 

Detector Mode

U108 pin 1

U108 pin 15

U108 pin 16

 

 

 

 

 

 

SAMPLE

H

L

H

 

POS PEAK

H

L

L

 

NEG PEAK

L

H

H

 

 

 

 

 

5. Set the HP 8560A to the following settings:

SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz SWEEP TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms

6.Check for the presence of the SCAN RAMP signal by connecting an oscilloscope probe to A3J2 pin 45 ( component side of A3J2). Connect the negative-probe lead to A3TP4.

7.A 0 to 10 V ramp should be present in both LINE and FREE RUN trigger modes. If the waveform is present only in LINE trigger, ADC control signal HBADC-CLKO may be faulty. Refer to “ADC Control Signals” in this chapter.

8.If the scan ramp is present, but is not being switched to the output of U108, replace

U108. If the scan ramp is absent in either mode, do the following:

a.Connect the oscilloscope probe to A3J400 pin 15 (HSCAN).

b.A TTL signal (high during 50 ms sweep time and low during retrace) should be present, indicating A3 is working properly. Refer to the Synthesizer Section troubleshooting procedure. A faulty TTL signal indicates a bad A3 Interface assembly.

9.Set the HP 8560A to the following settings:

SWEEP TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100ms

SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lOOMHz

IF Adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ON

10.Check for the presence of the CAL OSC TUNE signal by monitoring A3J401 pin 25 with an oscilloscope. If ERR 499 CAL UNLK is displayed and a signal greater than 10 V peak-to-peak during part of the retrace period, is present, the fault is on the A3 assembly.

11.If a constant dc voltage is present during the sweep and all of the retrace period, refer to the IF Section troubleshooting procedure.

7-20 ADC/lnterface Section