Output Goes Unleveled (Err 900 Or Err 901) - HP 8560E Service Manual

RF Section
A10 Tracking Generator (Option 002)
Coupler
The 1st LO signal from the A7 LODA is coupled off and buffered to
drive the output mixer. The main line of the coupler is fed to the 1ST
LO OUTPUT on the front panel. The loss through the coupler main line
is less than 2.5 dB.
Output Mixer
The 3.9107 GHz signal from the modulator is fed into the RF port of the
output mixer. The LO port of the output mixer is driven by the buffered
1st LO signal from the coupler. The output of the mixer is then
amplified.
Output Amplifier
The output amplifier low-pass filters the signal emerging from the
output mixer and then amplifies it into a usable range. The amplifier
also contains a detector for leveling the output.
Bias Board
The bias board contains the ALC circuitry for the tracking generator
and distributes dc power from the A14 frequency control assembly to
the rest of the tracking generator. The ALC inputs come from the A14
frequency control assembly (for controlling the power level), the EXT
ALC INPUT on the rear panel, and the detector in the output amplifier.
The ALC loop drives the modulator.
The following troubleshooting information is aimed at isolating
tracking-generator-related faults to either the A10 tracking generator
assembly, or one of the other supporting assemblies, such as A14, A15,
or A7. The A10 tracking generator is not field-repairable; a
rebuilt-exchange assembly is available.

Output Goes Unleveled (ERR 900 or ERR 901)

The ADC on the A3 interface assembly is used to monitor the control
line ALC MON (ALC Monitor) from A10. If ALC MON is greater than
+1.091 Vdc or less than -0.545 Vdc, ERR 900 TG UNLVL will be
displayed, indicating that the output of the tracking generator (or "TG")
is unleveled. The TG can typically be set for +2.8 dBm output power
and remain leveled. In any case, the output should remain leveled for
output power settings of less than the maximum leveled output power.
Refer to the specifications chapter in the HP 8560 E-Series Spectrum
Analyzer Calibration Guide for more information on this specification.
It is normal for the TG to be unleveled at frequencies less than 300
kHz. If the TG output is unleveled and the start frequency of the TG is
less than 300 kHz, ERR 901 TGFrqLmt (TG Frequency Limit) and ERR
900 TG UNLVL may be displayed. (Refer to Chapter 6, "General
Troubleshooting," for information on checking for multiple error
608 Chapter 11