HP 83522A Service Notes page 185

A4 ALC TROUBLESHOOTING (CHANGE 8) (Cont'd)
NOTE
To ensure that Option 002 plug-ins remain in the same attenuator
setting during troubleshooting, press [SHIFT] [POWER SWEEP].
This allows full ALC control without changing attenuator settings.
Since the Automatic Leveling Control (ALC) function of the Model 83522A RF Plug-In includes
many individual components arranged in a highly interdependent closed loop, the scope of the
A4 ALC Troubleshooting section extends well beyond the limits of the A4 assembly. Portions of
the A5
F M
Driver assembly, and several microcircuit components which contribute to the
power leveling function, are discussed below.
The ALC loop is a complex feedback loop which monitors the RF output power and continu-
ously corrects for any deviation from the desired power level. Because it is a closed system, it is
difficult to isolate cause from effect when a problem arises. Therefore, the key to troubleshooting
is to examine individual components, correlating the expected output for a particular input
signal.
This troubleshooting outline is organized into two major sections: Troubleshooting Symptoms,
and Troubleshooting Diagnostics. The section entitled "Symptoms" (1) characterizes possible
failure modes, (2) provides some general troubleshooting hints, and (3) refers the reader to more
detailed procedures found under "Diagnostics."
Troubleshooting Symptoms
The procedures outlined below help to systematically characterize the failure as quickly as
possible. The following failure symptoms are discussed:
RPGIPOWER DISPLAY FAILURE
UNLEVELED (LED)
FLATNESS/OSCILLATIONS (Power Dropouts)
FULL UNLEVELED POWER
NO POWER
POWER SWEEP/FLATNESS
Evaluating the specific failure may require an HP 432A/B/C, 436A, or 438A Power Meter or the
HP 8756A Scalar Network Analyzer with the Model 11664B Detector. (However, a crystal
detector with an "A vs B" oscilloscope may often be substituted.) Figure 8-26 configures a typical
test setup. Initiate all tests with the [INSTR PRESET] condition.
STOP
SWEEP
STOP
SWEEP
POS Z
BLANK
SWEEP
OSCILLATOR
A
Figure 8-26. Typical ALC Troubleshooting Setup
CHANGE 8