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