Specification—492/492P Service Vol. I (SN B030000 & up)
boards mounted on the metai extrusion can be removed by
removing the securing screws. All other circuit boards
(which should require minimal service) are accessible by re
moving a cover plate.
NOTE
Disassembly of some modules may require special
tools and procedures. These procedures will be found
in the Maintenance section.
In instruments that have phase lock, the phase lock as
sembly contributes to the 492/492P stability. Circuits are
completely rf isolated to ensure spurious free response, yet
the close proximity minimizes losses or interactions with
other functions. All compartments are enclosed on both
sides by metal plates and all interconnections between com
partments are made by feedthrough terminals rather than
cables. If the compartments are opened, be sure that the
shields and covers are properly reinstalled before operating.
Elapsed Time Meter
A 5000 hour elapsed time indicator, graduated in 500
hour increments, is installed on the Z Axis/RF Interface cir
cuit board. This provides a convenient way to check operat
ing time. The meter on new instruments may indicate from
200 to 300 hours elapsed time. Most instruments go
through a factory burn-in time to improve reliability. This is
similar to using aged components to improve reliability and
operating stability.
Changing Power Input Range
The following procedures describe how to set the input
power range.
a. Disconnect the power plug and remove the cover.
b.
Remove the access plate at the upper left corner
(viewed from the rear) of the power module.
c.
Shift plug P1029 to the appropriate pins on J1029 as
indicated by the silk screen nomenclature. Replace the ac
cess plate.
NOTE
The earlier version power supply module did not have
this access plate. To access P1029 proceed as
follows:
1) Set the instrument on its face and remove the four
screws that hold the power supply module to the side
rails. Lift the module off the instrument.
2) Remove the top and bottom screws then the side
screw that holds the two sections of the power supply
module together. Separate the two sections to ex
pose the power supply circuit board.
3) Shift the plug P1029 (upper left comer) to the ap
propriate pins on J1029. Re-install the two sections
and the power supply module.
d.
Remove the input power specification plate over the
input fuse on the back panel. Turn the plate over and
reinstall so the exposed information on power specifications
is correct.
e.
Change the input fuse to the new value specified on
the information plate.
f.
Replace the cover and the power cord; then connect
the instrument to the appropriate power source.
NOTE
The power cord supplied with the instrument and in
strument power voltage requirements depend on the
available power source (see the Specification part of
this section for power cord options).
Replacing Fuses
Besides the input (back panel) fuse, the 492/492P power
module has five fuses for the dc supplies (+300 V, F3014;
+ 100 V, F1034; +17 V, F1014; + 9 V, F1031; - 7 V ,
F1011). Access to these fuses can be gained by removing
the access plate at the upper right corner of the power mod
ule, or by separating the two sections as described for
changing the input power range. Fuses are identified with
stamped circuit numbers on the circuit board.
Selected Components
Some components, such as microcircuits, are selected to
meet Tektronix specifications. These components are indi
cated in the parts list and carry a Tektronix Part Number
under the Mfr. Part Number column.
Selected value components that compensate for param
eter differences between active components are identified
1-2
REV FEB 1982
