Tektronix 213 DMM Instruction Manual page 48

Maintenance-213 Service
1. Remove the crt retainer ring by gently squeezing it to-
gether and pushing it out of its hole in the line converter
chassis. Remove the line converter cover by pulling it away
from the chassis. Remove the mylar insulator from inside
the cover, as it is reinstalled separately during reassembly.
2. Remove the two plastic screws holding the circuit board
bracket to the line converter chassis. Remove the line con-
verter chassis by sliding the secondary power supply cable
with its grommet, toward the crt support ring hole and pull-
ing the cable and plug through the hole. Then separate the
ceramic shield, electrical contact and circuit board bracket.
Be careful that the ceramic shield does not fall free as it
may crack or break.
WARNING
I
Some of the disassembled parts in the Secondary
Power Supply are coated with silicone grease
which can cause eye irritation; therefore, han-
dle these parts with care and avoid getting the
grease in the eyes. Wash hands thoroughly after
completing work involving contact with silicone
grease.
3. Remove the two screws holding the transistor tabs to the
circuit board bracket. Be careful not to lose the small mica
insulation strip under one of the transistor tabs and the insu-
lator bushing on the screw for that same transistor.
4.
Remove the screw and nut holding the circuit board and
the wired substrate together by holding the nut and gently
turning the screw. Be careful not to apply too much pres-
sure to the substrate as it may crack. Gently slide the circuit
board bracket from between the substrate and circuit board,
then separate these parts by carefully pulling them straight
apart.
NOTE
Repair of the Rectifier Network (wired substrate)
is not recommended.
If
faulty, replace as a unit.
Reassembly. Reassemble the Secondary Power Supply in
the reverse order of the Disassembly. Apply the following
precautions:
1. For step 4. It the converter transformer (T 430) or sub-
strate has been replaced, or the bracket cleaned, coat both
sides of the bracket tab with a thin film of silicone grease
before reassembly. Also, only lightly tighten the screw
holding the substrate and circuit board together so they will
self-align when the bracket is attached to the chassis in step
2, and when the cover is installed in step 1.
4-10
2. For step 3. Insure that the mica insulating strip and insu-
lating washer is installed properly and on the correct transis-
tor. If the transistors or the mica strip have been replaced,
or the bracket cleaned, coat the transistor tabs, mica insula-
tor, and the bracket with a thin film of silicone grease be-
fore assembly.
3. For step 2. If either the circuit board bracket, electrical
contact, ceramic shield, or line converter chassis have been
cleaned or replaced, coat the mating surfaces of the cleaned
or replaced parts with a thin film of silicone grease before
reassembly. Be sure all the parts are installed properly.
Only lightly tighten the two plastic screws so the assembled
unit will self-align when the cover is installed in step 1.
4. For step 1. Install the mylar cover insulator and be sure
the electrical contact is outside the mylar so it will make
contact with the inside of the cover. Install the cover tight-
ly against the line converter chassis and tighten the two
plastic screws. Do not overtighten these screws as the
threads will strip easily. Insert the crt support ring from
the chassis side opposite the supply components.
SECONDARY POWER SUPPL V REPLACEMENT. Replace
the Secondary Power Supply in the reverse order of Removal.
Be sure that the electrical contacts are properly installed be-
tween the supply and the Amplifier and A/D Converter
Boards.
AMPLIFIER BOARD REMOVAL. To remove the Ampli-
fier Board, perform the Removal steps for the cabinet and
batteries, then proceed as follows:
1. Set the instrument on its bottom and unplug the crt
base socket and the crt terminal connector holder just be-
low and to the left of the crt base socket.
2. Turn the instrument on its top and remove the two Am-
plifier Board hold -down nuts (see Figure 4-2).
NOTE
Be careful when removing the Amplifier Board
as there is another terminal connector holder
to be removed after the board is free of the ter-
minal pins.
3. Carefully lift the board straight up and just free of the
terminal pins, then tilt slightly and remove the remaining
terminal connector holder on the cable from the Power
Supply Board. Remove the electrical contact from the
line converter chassis (see Figure 4-7) and set it aside for
reinstallation.
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