1.2 Modification History
Two major modifications have been implemented on the Spectrum boards:
(a) A modified layout of board (i.e. Issue 1, Issue 2 and Issue 3)
Issue 1. This layout allowed for the 16k RAM to be mounted
direct on the board, with the 32k extension consisting of a
subsidiary board mounting onto special OIL connectors.
Approximately
26,000
units
were
manufactured.
Issue 2. This layout allows for all 48k of RAM to be mounted
direct
on the
board; sockets, ready
for a
memory
update,
are
fitted on 16k versions. A small number of Issue 2 units were
manufactured using disc capacitors for 47 pF and 100 )jF values,
but subseguently axials were introduced.
Issue 3. This layout incorporates advanced circuitry for the
colour tuning, removing the need for potentiometers and trimmers
and the associated adjustment. It also allows for OKI ICs to be
used in the 32k extension memory. The heatsink is also
redesigned and is relocated at the back of the case.
(b) The Ferranti ULA, type 5C102, plus spider addition replaced by
ULA type 5C112.
5C102. This ULA has a timing fault which was cured by connecting
a
74LSOO
1C
mounted
on a
miniature board
and
spider.
This
ULA
was
fitted
to
approximately
40,000
units.
5C112. This improved ULA has no spider modification, but has
either a diode or resistor or transistor connected to it. The
details are:
Diode/resistor
mod : 4k7
resistor
from
+12V
to pin 30 on IC2 and
diode (IN 4148) from pin 30 of IC2 to pin 33 of IC1.
Transistor
mod : TR6
(ZTX313)
connected
as
follows:
Base to IC2, pin 30.
Emitter to IC1, pin 33.
Collector to IC2, pin 11.
6C001
This
ULA
alters
the
timing
of the
colour burst signal,
and
improves the performance of the Spectrum with certain television
sets (e.g. Hitachi, Grundig) . It also causes the screen picture
to be shifted by one character width to the left.
NOTE:
The
values
of
certain
components
vary depending
on
which
board and which ULA is used as follows:
4.3
To Next Page
Loading...
