Model
3720A
.2-10 The MC number gives the physical location of
each package in the form of
a
grid reference.
2-11 With the printed circuit board held compon-
ent side uppermost, and tongued connector near-
est,
numbering of the rows and columns of inte
grated circuits starts from the top left hand corner
of the board. The first figure following the MC
prefix
gives
the row and the second gives the
column. For example, MC52 will
lie
in the 5th
row down and the 2nd column across, whilst
MC103 will be in the 10th row and 3rd column.
2-1 2 The second method
of
identification of the
individual 'component blocks' helps the circuit
description and signal flow indication.
2-13 Each 'block'
is
given
a
prefix according to
its function
(see Table 2-2 for
a
full
list) and
a
number indicating
its
position on the schematic
diagram, in the same manner
as
resistors, capacitors,
etc, are referenced.
Table 2-2 Digital integrated circuit abbreviations
I
Abbreviation
F
unction
B
DD
FF
G
IG
MS
SR
Buffer
Decade Divider
FI ip-f lop
Gate
Inverter Gate
Monostable
S
h if
t
Register
2-14 All
IC
leads are referred to in the same way
as
assembly connections. For example, lead 12 on
integrated circuit MC25, on A5 assembly, is
referred to
as
A5MC25(12). Similarly when de-
scribing schematics, lead
6
on Flip-flop 9 on
assembly A2 would be referenced A2FF9(6).
2-15 INSTRUMENT DISMANTLING
DANGER
115/230V AC AND +158V DC SUPPLY
WIRES ARE EXPOSED WHEN ANY
OF
I
THE INSTRUMENT COVERS ARE
RE-
MOVED. USE EXTREME CAUTION DUR-
ING TROUBLESHOOTING, ADJUSTMENT
OR
REPAIR. AVOID DAMAGE TO THE
INSTRUMENT BY DISCONNECTING THE
POWER CABLE BEFORE REMOVING
OR
REPLACING COVERS, ASSEMBLIES
OR
COMPONENTS.
2-16 Removing Top and Bottom Covers
1.
Remove the four cross-head screws holding the
cover in position.
2. Slide the cover about lin (2.5cm) to the rear
and lift clear.
NOTE:
It is not necessary to remove the feet
or
the tilt stand from the bottom cover before
rem ova
I.
2-1
7
Removing Side Covers
1. Remove the four cross-head screws securing
each cover.
2. Lift cover clear.
2-18 Front Panel Access
1.
2.
3.
4.
5.
6.
Remove the
top
and
bottom
covers from the
instru ment.
Release the two screws securing the Al/All
retaining strip and lift this strip clear.
Remove assemblies A2 to A1
1
inclusive.
Release the two screws
at
the base of each
of the right hand and left hand board guides.
Withdraw the board guides to
give
access
to
the rear
of
the front panel.
Re-assembly is
a
reversal of the above pro-
cedu re.
c
2-
2
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