Installation guide

Troubleshooting
Troubleshooting the AT1 High-Power Mechanical Attenuator (Option UNB)
1-82
Troubleshooting the
AT1 High-Power Mechanical Attenuator (Option UNB)
The AT1 High-Power Mechanical Attenuator (Option UNB) has an attenuation range of 130 dB in 5 dB steps.
This attenuator is used to coarse-tune the power level while the Automatic Leveling Control (ALC) loop is
used to fine-tune the power level; the ALC fine-tunes the power level within each 5 dB step.
The attenuator is set to 0 dB attenuation for power levels from 0 dBm to +25 dBm. The first 5 dB step is
switched in at approximately −0.5 dBm, the second step is switched in at approximately −5.5 dBm, the third
step is switched in at approximately −10.5 dBm; this pattern repeats until the last 5 dB step is switched in at
approximately −125.5 dBm. Attenuator control comes from the A23 Motherboard through A23J25.
❏ Check the power supply voltage on A23J25 pin 1.
— If the power supply voltage on A23J25 pin 1 is good:
1. Set the amplitude to +2 dBm.
2. Set the amplitude increment to 5 dB.
3. Set the
RF On/Off to RF On.
4. Set the amplitude level using the Down arrow key.
5. Use Table 1-38 to isolate the problem.
— If the attenuator control line voltages are correct for the given amplitude setting,
check the attenuator ribbon cable (W57):
— If the attenuator ribbon cable is good,
replace the AT1 High-Power Mechanical Attenuator (Option UNB).
— If the attenuator ribbon cable is bad,
replace W57.
— If the attenuator control line voltages are wrong for the given amplitude setting,
check the that the control voltages change within a 5 dB range (Refer to Table 1-38.):
— If the attenuator control line voltages change within 5 dB, return the unit back to
Agilent Technologies for calibration.
— If the attenuator control line voltages do not change within 5 dB,
replace the A23 Motherboard.
(Refer to “Self-Tests 21xx for the A23 Motherboard” on page 1-66.)
— If the power supply voltage on A23J25 pin 1 is bad, troubleshoot the A6 Power Supply.
(Refer to “Power Supplies” on page 1-23.)
Table 1-37
Power
Supply
Voltage
(Vdc)
Connector Pins
on the
A23 Motherboard
Minimum
Value (Vdc)
Maximum
Value (Vdc)
Origin
+15 J25-1 +14.1 +15.9 Main Supply