3. REPAIR
3.1 Renewal of components should be carried out using recognised
desoldering/heatsinking techniques to prevent damage to the component
or to the printed circuit board. Other points to be noted are:
(a)
When
replacing
a
keyboard
matrix, take care
that
the
ribbon
connectors are fully inserted into the board connectors, and are
not kinked during insertion.
(b)
Make
sure
there
is a
good
contact
made
between
the
voltage
regulator body and the associated heatsink in order to ensure
adequate heat conduction. The heatsink hole in certain Issue 3
boards allows excessive play which could cause fouling of the
edge connector.
Take
care
in
re-assembly
that
the
heatsink
is
fitted
away from
the
edge connector.
(c)
When
the
regulator
is
being replaced
it is
recommended
that
a
suitable proprietary thermal grease is applied to the rear
surface of the component body.
(d) The modulator should be replaced as a complete unit.
(e)
When
replacing
plug-in
ICs it is
advisable
to use the
correct
removal and insertion tools. Avoid contaminating the connection
pins by hand!ing.
(f)
When
handling
ICs
take
normal
anti-static
precautions.
It is
recommended that only a suitably earthed, low power soldering
iron be used.
(g)
After
any
component
has
been
renewed
the
circuit
board
should
be
examined carefully, to ensure that there are no solder
'splatters' which may cause short circuits between tracks or
connector pins.
4. 16k TO 48k UPGRADE
4.1 Integrated Circuits/Link Settings
For both the Issue 2 and the Issue 3 boards the memory upgrade is
accomplished
by
plugging
four
logic
ICs and
eight
memory
ICs
into
existing
board sockets.
Depending
on the
types
of
memory
1C
used,
appropriate
circuit
links
must
be
fitted
on the
board. Figure
4.3
shows the layout of the area of the board containing the empty
sockets. The Issue 3 board is shown which also gives positions (top
left of diagram) of the links.
4.19
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