BBC Microcomputer Service Manual Oct 1985 Section 1 BBC Micro ...

ii) Insert the above ICs into the sockets provided on the main
circuit board. Solder the connectors on to the printed circuit board.
iii) Cut the wire links at link positions S12 and S13. Move the MOLEX
link at position S25 from South to North.
iv) On issue 1, 2 or 3 circuit boards only, add a 2k2 ohm resistor
between PL9 pin 1 and +5v on the solder side of the circuit board using
a resistor with sleeved leads. +5v is available at IC85, pin 16 (33 mm
due North of pin 1).
v) On issue 1, 2 or 3 circuit boards only, cut the track connected to
PL9 pin 23 (this may have previously been cut), then link IC69 pin 40
to PL9 pin 19. This modification may have been made, and, if so, a
check should be made to ensure that it has been correctly performed.
vi) On issue 1 and 2 circuit boards only, PL9 pin 26 should be cut out
of the header. Care should be taken to ensure that the pin is cut right
back so that no connection can be made to it.
vii) On issue 1 and 2 circuit boards only, a BC239 transistor should be
added in place of link S1 as follows:- Cut the track between the centre
and South pins of S1 on the solder side of the circuit board. Cut the
two tracks connected to the North pin of S1 on the solder side of the
circuit board, then reconnect the ends of these tracks leaving the
North pin isolated. Insert a BC239 transistor into the S1 position with
the base in the South pin, the emitter in the North pin, and the
collector in the centre pin. Finally, link the North pin of S1 to IC27
pin 7 with a short length of insulated wire.
viii) On issue 1 or 2 circuit boards only, add a 4k7 ohm resistor (
R162) between the existing two holes located approximately 5 mm East of
IC70 pins 11 and 13, as shown below.
26