Tektronix 7A22, Instruction Manual

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CAUTION
Silk-screen lettering dissolves when contacted by
fI ux -remover.
Metal Terminals. When soldering metal terminals (inter­
connecting plug pins, switch terminals, potentiometers, etc.)
ordinary 60/40 solder can be used. The soldering iron
should have a 40- to 75-watt rating with a 1fa inch wide
chisel-shaped tip.
Observe the following precautions when soldering to
metal terminals:
1. Apply heat only long enough to make the solder flow
freely.
2. Apply only enough solder to form a solid connection;
excess solder may impair the function of the part.
3.
If a wire extends beyond the solder joint, clip the ex­
cess close to the joint.
4. Clean the flux from the solder joint with a flux-remover
solvent to maintain good environmental characteristics and
appearance.
Specific Component Replacement Information
WARNING
Disconnect the instrument from the power source
before removing or replacing components.
The pushbutton switches are not repairable and should
be replaced if defective. Components which are mounted
on the circuit board associated with the pushbutton switch
can be replaced using the normal replacement procedure.
See the information under Light-Bulb Replacement for bulb
replacement. Use the following procedures to replace the
-tINPUT and --INPUT pushbutton switches.
1. AC-GND-DC (+ INPUT) Switch
a. Set the front panel controls as follows:
POSITION
STEP A HEN DC BAL
VOLTS/DIV
HF --3 dB POINT
LF --3 dB POINT
DC OFFSET (FINE)
DC OFFSET (COARSE)
Midrange
Midrange
lOV
1 MHz
DC OFFSET
Midrange
5 turns from either extreme
b. Remove all front panel knobs.
c. Remove the GND binding post assembly.
d. Remove the nut and washer from the POSITION and
DC OFFSET shafts.
e. Remove the plastic bushing from the VOLTS/DIV shaft.
f. Remove the front panel overlay.
g. Without unsoldering any leads, carefully push the
dual DC OFFSET potentiometers out of the front panel and
lift them out of the way.
h. Unsolder and unplug the connecting leads from the
AC-GND-DC switch.
i. Remove four corner screws and remove the front sub­
panel.
®I
Maintenance--Type 7 A22
j. Remove the two screws securing the AC-GND-DC
switch to the front sub-panel and remove the switch.
k. Replace by reversing the above procedure.
2. AC-GND-DC (-INPUT) Switch
a. Perform step 1, parts a through f, of Specific Compo­
nent Replacement.
h.
Loosen the setscrew on the collar connecting the GAIN
shaft to the pot coupler and pull the shaft out of the front
panel.
c. Unsolder and unplug the connecting leads from the
AC-GND-DC switch.
d. Remove the four corner screws and remove the front
sub-panel.
e. Remove the two screws securing the switch to the front
panel.
f. Remove the switch.
g. Replace by reversing the above procedure.
3. Light-Bulb Replacement, + INPUT and -INPUT
Push-BuHon Switches
Two types of pushbutton switches which have different
light designs are in use. One switch design uses a metal
cover over the light bulb(s) on the back of the switch; the
other type does not. Either or both types of switches may
be used in the 7A22.
To replace light bulbs in the pushbutton switches, use the
following procedure:
a. Remove the applicable INPUT switch as described in
steps 1 and 2.
b. On switches with the metal cover, remove the screw
holding the cover and remove the cover.
c.
Clip off the bulb leads near the bulb body.
d. Remove the leads from the circuit board.
e. Remove the excess solder from the circuit board with
a vacuum-type desoldering tool.
f. Solder the new bulb to the circuit board (replace
cover).
g. Replace the switch in the instrument.
4. Bandwidth Circuit Board
a. Set the LF and HF --3 dB POINT Selectors to either
extreme.
b. Loosen the setscrews securing the LF --3 dB POINT
shaft to the collar on the cam switch. Pull the shaft forward
until it clears the collar.
c. Loosen the setscrews securing the HF
--3
dB POINT
shaft to the collar on the cam switch. Pull the shaft forward
until
it
clears the bandwidth board.
d. Loosen the setscrew securing the GAIN shaft to the
collar on R540. Pull the shaft forward until it clears the band­
width circuit board. Loosen the setscrew securing the collar
to R540 and remove the collar.
e. Loosen the four circuit board retaining screws and lift
out the Bandwidth Circuit Board.
f. Unclip the leads from solderless connectors A, AN,
AP, AO, and D.
g. Replace by reversing the above procedure.
4-3