HP 70427A User Manual page 602

NOTE
Description
Procedure
Lo Amplifier Bias Adjustments
(To be done when the LO Power Amplifier, LO Pre Amplifier or YIG Driver
Assembly have been changed)
Bias Adjustments for the LO Power Amplifier and LO Pre Amplifier reside
on the YIG Driver assembly. If these adjustments are done because of a
repair, they should be done prior to any Internal Power Calibrations. In
addition, if these adjustments are performed as a result of replacing the LO
Power Amplifier, or LO Pre Amplifier, the Internal Power Calibrations must
be done afterward to assure that the instrument can set power correctly. For a
unit with Option 002 there are two YIG Driver assemblies and two sets of
Amplifiers. In this case A9 should be adjusted first and A8 second. Note that
no external voltmeter is need for these adjustments. The instrument uses it's
own internal voltmeter to display readings made during adjustment of each
of the six amplifier stages.
1. Before performing adjustments, press the green
2. Go to the Latch Control Screen by pressing the following screen keys:
Service
Hardwre Control
3. Set the Hardware Control screen to allow control of the YIG driver
assembly as follows: Press
Or if you have an Option 002 equipped unit determine if you are
adjusting YIG1 (right most) or YIG2 (left most) and press
YIG Tuned Filtr1
4. Now set the LO Amplifiers to maximum gain with the following key
sequence:
6
LATCH NUMBER ENTER
4095
LATCH DATA ENTER
5. Locate the six adjustments on the YIG Tuned Filter Driver assembly
according to the following figure. Push W56 to the side to allow access
but do not disconnect W56 as this will cause the adjustments to be off
slightly.
Lo Amplifier Bias Adjustments
until
BLOCK
YIG Tuned Filter
or
YIG Tuned Filtr2 appear.
HP 70427A/HP 70428A User's Guide 15-5
Adjustments
key.
[INSTR PRESET]
appears.
until
BLOCK