Tektronix 7B51 Instruction Manual page 48

A. CAM-TYPE SWITCH. The cam-type switch (TIME/
DIV) consists of a rotating cam, which is turned by the
front panel knob, and a set of contacts mounted on an
adjacent circuit board. These switch contacts are actuated
by lobes on the cam. The TIME/DIV switch can be disas-
sembled for inspection, cleaning, repair or replacement as
follows:
1. Remove the four screws which hold the metal cover
over the switch. The switch is now open for inspection or
cleaning.
2. To completely remove the switch, loosen the set
screw on the collar securing the VARIABLE shaft to the
VARIABLE potentiometer and pull the shaft completely
out the front of the unit. Loosen the two set screws on the
TIME/DIV knob and remove the knob. Remove the plastic
bushing from the access hole for the TIME/DIV shaft.
3. Remove the sweep generator board by loosening the
four knurled screws and carefully lifting out.
4. Remove the six screws which hold the cam switch to
the interface circuit board and remove the cam switch.
5. To remove the cam from the front support block,
remove the retaining ring from the shaft on the front of the
switch and slide the cam out of the support block. Do not
lose the small detent roller.
6. To replace defective switch contacts, unsolder the
damaged contact and clean the solder from the hole in the
circuit board. Following the procedure given in the instruc-
tion sheet included with the cam switch replacement kit,
use the alignment tool to position the new contact in place.
Solder the contact using the soldering techniques given
previously in th is section of the manual.
7. To re-assemble the switch, reverse the above pro-
cedure.
B. PUSH-BUTTON SWITCHES. Use the following pro-
cedure to replace the five pushbutton switches:
1. Loosen the set screws and remove the POSITION,
LEVEL/SLOPE, TIME/DIV and VARIABLE knobs.
2. Remove the front panel to gain access to the switch
mounting screws.
®
Maintenance-Type 7B51
3. To remove the B DELAY MODE switch, remove the
two phillips head screws and disconnect the multi-pin con-
nector.
4. To remove the MAGNIFIER switch, remove the
phillips head screw and disconnect the mUlti-pin connector.
5. To remove the TRIGGERING switches, remove the
two phillips head screws from each of the MODE,
COUPLING and SOURCE switches. Disconnect the follow-
ing mUlti-pin connectors: DELAY TIME MULTIPLIER, B
DELAY MODE, SWP CAL, POSITION, LEVEL/SLOPE,
TRIG'D and MAGNIFIER. Disconnect the pin connectors
from the SOURCE and COUPLING switches. Remove the
four screws securing the front of the unit to the top and
bottom and remove the front of the unit. Remove the
TRIGGERING switches (the sweep generator board may
have to be removed to take out the TRIGGERING MODE
switch).
Light Bulb Replacement. To replace the light bulbs fol-
low the above procedure to remove the switches. Remove
the screw and cover from the back of the switch to expose
the light bulb. Unsolder the two leads and remove the light
bulb. Cut the leads of the replacement light bulb to the
same length as those of the old bulb. Place insulating sleeves
over the leads and replace the new bulb in the exact posi-
tion of the old bulb.
Reassemble by reversing the above procedure.
Instrument Repackaging
If the Type 7851 is to be shipped for long distances by
commercial means of transportation, it is recommended
that the instrument be repackaged in the original manner
for maximum protection. The original shipping carton can
be saved and used for this purpose. Repackaging informa-
tion and/or new shipping cartons can be obtained from
Tektronix, Inc. Contact your local Tektronix Field Office
or representative.
NOTE
The plug-ins should not be shipped installed in an
oscilloscope. The oscilloscope packaging material is
not designed to protect the plug-ins.
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