Sinclair ZX81, Руководство по сборке, Страница: 4 / 43

4. CIRCUIT BOARD ASSEMBLY
The circuit board will be supplied with one side printed with all the component locations - this is the
side the components go. This printing is reproduced as fig. 6 (See reverse side of sheet) since some of
the markings will be covered by components. All soldering is done on the other side which is coated
with a green solder resist - this keeps the solder away from where it is not needed. The exception is
the edge connector area which should be kept free of solder to ensure reliable connection to the RAM
pack or printer if they are used, We suggest you assemble the components in the following order,
although it is not compulsory -
(i) Resistors, capacitors and 1C sockets - do not plug the I C.s in yet.
(ii) The diodes and transistors.
(iii) The 'large' components: the sockets, keyboard connectors, modulator, the regulator and
heatsink.
(iv) Finally plug the ! C s into their sockets.
The general procedure for each component:-
(a) Identify the part and its position on the board and insert it into the appropriate holes, bending the
leads if necessary. (But see later). In the case of components with a number of pins, make sure that
they have all gone through their holes.
(b) Hold the part in position - if you bend its leads to do this, do not press them fiat onto the board as
this will make them difficult to cut and will encourage short circuits.
{c) Solder all the wires on the 'green side' of the board and, if they are long, trim them with the side
cutters. No lead should stick out more than about 3mm or V^'from the solder side.
Some components need more detailed explanation:-
(a) The capacitors are represented by a capacitor symbol on the board, rather than a box as the rest of
the components are. Fig, 7 explains how they fit in the board relative to the symbol.
(b) There are four oblong boxes labelled R7-R10, R11-R14, R18-R22and R23-R26. These all contain a
row of resistors standing 'on end' as in fig. 8. Take care when mounting these: the length of bare wire
up the side should not be allowed to short against anything else
(c) IC2 and IC4 have two different sized boxes printed on the board
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use only the holes corresponding
to the smaller box.
(d) As previously mentioned, IC4 may be in either one or two packages, Only the appropriate 1C
sockets will be supplied, so make absolutely sure you know which version you have got before
proceeding.
IMPORTANT:- If you have the 24 pin 4118 in your kit, a short wire link should be inserted in the holes
at position L1 Use a component lead off-cut for this. DO NOT do this if you have two 18 pin 2114s, and
do not put anything in position L2.
(e) When mounting the regulator, do not bend its leads too close to the plastic. Bolt it down firmly with
its heatsink before soldering.
(f) Put the modulator's wires through the holes marked "Fr/UK1" and "UK2" Put each lead through
the hole it is nearest to: do not cross them over Do not try to bend the thick pins on the modulator:
hold it in place by hand whilst soldering. The black card trim is a push fit over the aerial socket.
(g) The I.C.s will have their pins splayed out slightly and you may need to push them inwards slightly,
e.g. by pressing against a flat surface, before they will fit the sockets. Make sure that each pin has in
fact gone into its respective socket and that none are curled up under the I C.
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