2-30 Line Transformer Removal/Replacement
1.
2.
3.
.4.
5.
6.
7.
8.
9.
10.
Tilt the 3720A onto
its
right hand side.
Remove the
top
and
bottom
covers from the
instru ment.
Release
the
two screws holding A20 in place
and lift out A20.
Remove the back panel high voltage cover.
Remove the internal high voltage cover.
Unplug the five wires from A17 and then
remove
AI
7.
Remove XA20 mounting plate and pull
it
gently to the side.
Note the wire colours against the corres-
ponding pin numbers on the top and bottom
of the line transformer and then unsolder
the connections.
Remove the four screws holding the trans-
former in position. Retain the underside
nuts and safety mouldings and pull the trans-
former out through the top of the instrument.
Re-assembly
is a
reversal of the above pro-
cedu re.
2-31 Chassis Mounted Transistors Plate
Removal/Replacement
1.
2.
3.
4.
5.
6.
7.
Remove the
top
cover and
right
side cover
from the instrument.
Release
the
two
screws securing the A12/
A16 retaining strip and lift this strip clear.
Remove assemblies A12 to A16 inclusive.
Release
the two screws
at
the bottom of the
transistor plate.
Withdraw the plate.
Renew the faulty transistors
as
necessary.
Re-assembly
is
a
reversal of the above pro-
cedu re.
2-32 High Voltage Tripler Assembly Removal/
Replacement
1.
Remove the
top
cover from the instrument.
2.
3.
4.
5.
6.
1.
8.
9.
10:
11.
12.
13.
14.
15.
Section
I1
Remove the internal high voltage cover.
Remove the rear panel high voltage cover.
Unplug the five wires from A17 and then
remove A1 7.
Unsolder the black and grey wires from the
ground
tag.
Release the two screws holding A20 in place
and lift out A20.
Remove XA20 mounting plate.
Release
the two screws securing the Al/All
retaining strip and lift this strip clear.
Remove assemblies A2 to A6 inclusive.
Remove A20 support block. Two screws
hold
it
in place.
Remove the two screws holding the high
voltage connector A55J1 in place. Disconnect
the flexible wiring from this connector.
Unsolder the wires from XA(20(L) and
XA20(N) after noting their colours.
Remove the wires from the grommet.
Lift out the high voltage tripler assembly.
Re-assembly
is a
reversal of the above pro-
cedu re.
2-33 REPAIR PROCEDURES
2-34 Etched Circuits
2-35The etched circuit boards in the Spectrum
Display are of the plated-through type, consisting
of metallic conductors bonded to both sides of the
insulating material. The metallic conductors are
extended through the component mounting holes
by
a
plating process. Solder connection can be
made from either side of the board with equally
good results. Following
are
recommendations and
precautions pertinent to etched circuit repair
work
:
a.
Avoid unnecessary component substitution;
it
can result in damage to the circuit board and/or
adjacent components.
2-5
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