AR 10037990, Operating And Service Manual, Page: 39 / 54

Model 250T6G18
Rev A 19
3.7 EMERGENCY BYPASS OPERATION
For reference, see schematic 10-24369-000 in Section 5.2.
The TWTA is provided with a means of operating the amplifier manually in the event that there is a failure of the
control module and it is imperative that the amplifier remain on line.
CAUTION:
Emergency bypass operation disables external interlock
and certain protective and diagnostic features. For this
reason, the emergency bypass mode of operation should be
used only when the control unit fails and when it is
essential to remain on line
.
To access the manual controls, remove the two 4-40 screws securing the Emergency switch cover plate on the
front panel. Emergency bypass mode is selected by pushing the left-hand switch (S1) to the left. The center switch
(S2) toggles between high voltage on (left) and high voltage off (right). The right-hand switch (S3) selects
between beam on (left) and beam off (right). There is a manual control for the gain adjustment as well. This is a
flat, square single-turn pot (R1).
CAUTION:
Do not adjust 20-turn pot R11; its function is to set the
foldback VSWR level, and it is calibrated at the factory.
3.8 REMOTE IEEE-488 OPERATION
The TWTA is provided with an IEEE-488 interface that permits remote emulation of OPERATE, STANDBY,
and RESET push-buttons as well as access to parameter measurements, system faults, and control unit status. The
following tables summarize the commands and the return codes.
Table 3-3. Catalog of IEEE-488 Commands
Command Function Units Response format
RDSTAT Returns status code of processing of previous command
(see Table 4) STATUS=[ ]
RDFLT Returns system fault code (see Table 3-5) flt=[ ]
OPERATE; Emulates OPERATE push-button
STANDBY; Emulate STANDBY push-button
POWER:OFF; Emulate STANDBY push-button
RESET; Emulates RESET softkey
RDS/N Returns serial number s/n=[ ]
RDCONHR Returns console hours ConHr=[ ]
RDRFHR Returns RF hours RfHr=[ ]
RDEK Returns cathode voltage KV Ek=[ ]
RDEB Returns collector voltage KV Eb=[ ]
RDEG (or RDEA) Returns grid (or anode) voltage V Eg=[ ] (Ea=[])
RDEF Returns heater voltage V Ef=[ ]