Agilent Technologies 856290216 service manual Logic Levels at A3U108, 22 ADC/lnterface Section

1. Set the spectrum analyzer to the following settings:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz Reference level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -10 dBm Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50s DETECTORMODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAMPLE

2.Refer to Table 8-9 and check for correct logic levels at A3U108 pins 1, 15, and 16. Check for proper output signals at TP6. If the select lines are not changing, suspect the ADC ASM or the VGA/ADC MUX Control. If the select lines are changing, but the proper video inputs are not being switched to the output, replace U108. In SAMPLE mode, the input is MOD-VIDEO (pin 7); in POS PEAK mode, the input is POS-PEAK (pin 5); and in NEG PEAK mode, the input is NEG-PEAK (pin 6).

3.Check for the presence of the YTO ERR signal at A3J2 pin 42 with an oscilloscope probe.

4.If ERR 300 YTO UNLK or 301 YTO UNLK occurs and the voltage is near zero during a sweep and positive during retrace (YTO is being locked), the fault is on the A3 assembly. If a constant dc voltage is present, refer to the synthesizer troubleshooting procedure in Chapter 11, “Synthesizer Section.”

Table 8-9. Logic Levels at A3U108

Detector Mode	U108 pin 1	U108 pin 15	U108 pin 16
SAMPLE	H	L	H
POS PEAK	H	L	L
NEG PEAK	L	L	H

5. Set the spectrum analyzer to the following settings:

Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5 MHz 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). C onnect 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 troubleshooting procedure in Chapter 11, “Synthesizer Section.” A faulty TTL signal indicates a bad A3 Interface assembly.

9.Set the spectrum analyzer to the following settings:

Sweeptime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100ms Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lOOMHz

8-22 ADC/lnterface Section