Tektronix T921 - Page 74

Service Information-T921/T922/T922R
2 .
Use a small screwdriver to remove the
clip holding
Q458 to the rear
subpanel .
5- 1 6
3 .
Remove the front panel knobs and
shafts .
4 . Remove the high-voltage
shield and the two posts
underneath the shield .
5 . Disconnect
J138 (white-blue wire),
J148 (white-
brown wire), J470
(a brown two-lead connector
and a
black two-lead
connector), J475, J465, J466, and the
Cal
Out lead (goes to PROBE ADJ
on front panel) . The J138
and J148 wires pass through the
board to the crt .
NOTE
To disconnect
J475, J466, and
J465, lift the cable
retainers with a
screwdriver until you can
remove the
cable . Also remove
the high-voltage lead
from U460
to the crt .
WARNING
The crt anode and the output
terminal of high-
voltage
multiplier U460 may retain a
10,000 volt
charge
after the instrument is turned off . To avoid
electrical shock,
ground both the output terminal of
U460 and the crt high-voltage
anode lead to chassis
ground .
6 . Remove the five retaining screws
.
7 .
Disconnect J7 from the Power Supply board by
lifting
the Interface board
out .
8 . Unsolder the power cord
conductors (a blue wire and
a brown
wire) from the back of the board .
To replace the Interface
board, reverse the above
procedure
.
Cathode Ray Tube (CRT)
Replacement
Use care when handling a crt .
Protective clothing
and safety
glasses should be worn . Avoid striking
it
on any object
which might cause it to crack or
implode .
When storing a crt, place it in a protective
carton or set it
face down on a smooth surface in a
protective location with
a soft mat under the
faceplate to protect it from
scratches .
To remove the crt from
the instrument, disconnect the
power cord plug from the power input source
and remove
the cabinet halves . Turn the front of theinstrument
toward
you, and perform the following steps .
1 . Remove the two screws holding the
high-voltage
shield over the Interface board, and
remove the shield .
WARNING
The crt anode and the
output terminal of high-
voltage multiplier U460 may retain a
10,000
volt
charge after the instrument is turned off . To avoid
electrical shock, ground both the output terminal of
U460 and
the crt high-voltage anode lead to chassis
ground .
2 . Grip the
insulated portion of the anode lead and
disconnect
it
from
the U460 output terminal, and ground
both terminals
to chassis . Pull the free end of the anode
lead out through the
chassis holes . This lead is part of the
crt and is supplied with the new
crt .
3 . Grip the 14-pin crt base socket, and pull it backward
off the base
of the crt .
4 . Disconnect the four-pin plug
from J470 on the
Interface board . This terminates
two black wires and two
red wires from the trace rotation (TR
ROT) and Y AXIS
controls .
5 . Remove the
three screws holding the Vertical
Amplifier to the chassis, and separate the
amplifier from
the Interface board by pulling downward
to disconnect the
04 connector .
6 . Disconnect the two
connectors from the pins on the
left side of the crt neck . These are the
vertical deflection
plate leads, the upper wire color is
blue on white and the
lower
wire color is brown on white .
7 .
Disconnect the two connectors from the pins on the
bottom
of
the
crt neck . These arethe Horizontal Deflection
Plate leads ; the left wire
color is red on white and the right
wire color is green on white .
8 . Carefully raise the
plastic crt front support ring
upward and to the right to disengage
the two buttons on
the bottom and the two buttons
on the left side from the
instrument chassis .
REV . B JUL 1977