Harris Gates Five 994 9204 002, Техническое руководство

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Disconnect the vertical input, then adjust
vertical positioning so that the oscilloscope
trace is exactly in the middle of the screen.
Reconnect the vertical input.
Increase the sweep speed of the oscillo-
scope. If the scope has a X10 multiplier, use
it to make the oscilloscope show 5 degrees
per division horizontally (50 degrees di-
vided by 10). Otherwise increase the sweep
speed as possible to increase the resolution
of the oscilloscope to a value comparable to
the 5 degree per division set up.
Adjust the horizontal position of the oscil-
loscope to place the zero crossing of the RF
drive signal in the center of the oscillo-
scope. The oscilloscope has now been set
up to measure degrees of phase shift relative
to the drive signal across the R13 position.
Move the oscilloscope probe to R14, the
next RF drive test point.
If the oscilloscope trace passes exactly
through the center of the screen, the phase
of the drive across R14 is the same (0 de-
grees) as across R13. If the zero crossing on
the oscilloscope occurs somewhere other
than the center of the screen, then that drive
signal differs from the R13 reference by an
amount which can be measured according
to the calibration setup.
Check the phase of the drive signals across
R23, R24, R33, R34, R43, and R44 on each
PA module.
Total variation in drive phasing should be
no more than +/-5 degrees.
Possible causes for RF drive phase imbal-
ance are:
Failed PA Transistors. A simple ohmme-
ter check of the transistors will nearly al-
ways identify defective ones. Failed
transistors should also present problems
which are more easily identified than drive
phase error, such as reduced power output,
PA VOLTS/AMPS ratio change, blown
fuse, low RF drive voltage, etc.
Frequency Determined Component
Wrong. Check to see that the PA input
tuning components such as L14, C10, R11,
L13, and R13 are properly soldered and are
in good physical condition. If any of these
components have recently been installed,
recheck their values. To determine if the
fault is with the PA module or the drive
cable, make an impedance
measurement of each drive input.
Bad RF Drive Cable. The RF drive cable
consists of eight individual coaxes. If the
shield of one coax is open, the drive will be
different for one set of transistors. Remove
the RF drive cable from the splitter board.
An ohmmeter check between all shields on
the splitter end of the cable should show
zero ohms if the other end is still plugged
into the PA. Be sure to flex the cable some
to check for intermittent connections.
Bad RF Drive Transformer. If possible,
make comparisons between the RF imped-
ance at each PA input (L14, L15, L24, L25,
L34, L35, L44, and L45). An input which
measures an unusual voltage or phase will
also have an unusual impedance. If you
have identified an input which has an un-
usual impedance, you will need to deter-
mine the cause. This can be accomplished
by swapping transistors, and making com-
parison impedance measurements while
short circuiting the terminals of the RF drive
transformers.
Figure C-3
Upper Trace - PA Output Amplitude Equal to PA Voltage
Lower Trace - PA Inputs, 26-32Vp-p
PWA, PA MODULE - 992 9714 001
Harris PN Description QTY UM Reference Designators (H)
000 0000 010 . . B/M NOTE: . . . . . . . . . . . . . . . . . . . . 0.0 EA C010 C015 C020 C025 C030 C035 C040 C045 L014 L015
L024 L025 L034 L035 L044 L045
350 0037 000 . . RIVET POP .125X.265 . . . . . . . . . . . 3.0 EA
354 0309 000 . . TERM SOLDER . . . . . . . . . . . . . . . . 56.0 EA
E002 E003 E004 E005 E006 E007 E008 E009 E010 E013
E014 E015 E016 E017 E018 E019 E020 E023 E024 E025
E026 E027 E028 E029 E030 E033 E034 E035 E047 E048
E049 E050 E051 E053 E054 E055 E056 E057 E058 E060
E061 E063 E064 E065 E067 E068 E069 E070 E072 E073
E074 E075 E076 E077 E078 E079
358 2837 000 . . STUD, PC BD 4-40 X 5/16. . . . . . . . 10.0 EA
C-4 888-2314-001 Rev. AE: 03-05-2002
WARNING: Disconnect primary power prior to servicing.