Watford DDFS Mk II Fitting Instructions

DDFS Mk II Fitting Instructions
PLEASE READ THE INSTRUCTIONS BEFORE STARTING
Before installing DDFS disconnect the computer from the mains
The following instructions are for users fitting a disc interface to an
unexpanded BBC B Micro, users who already have a disc interface
installed, should skip to the section titled 'Replacing an existing disc
interface'.
The first thing you must determine is the issue number of your
BBC Micro, on removing the lid of the computer, you should see
printed on the main circuit board near the centre an Acorn logo
followed by issue 1, 2, 3, 4 or 7. H you have an issue 4 or 7 BBC skip
to the paragraph entitled 'Modifications for Issue 4 and 7 boards'.
Users with an issue 1 2 or 3 boards read on.
Modifications for issue 1, 2 and 3 boards
Locate the track running between pin 9 of IC 27 and the right
hand pad of link S9 and carefully cut it. Next using a pair of wire
cutters, cut the leg of pin 9 of IC 27 as near to the circuit board as
possible and bend the leg up. Using a thin piece of connecting wire
link the leg of pin 9 to the right hand pad of link S9. This operation
is required to generate the non maskable interrupts to operate the
DFS. Proceed to the paragraph entitled 'Fitting for all issue boards'
Modifications for issue 4 and 7 boards
Locate link S9 (south of the printed Acorn logo) and see if there is
a wire link joining the two pads. If the wire link is present this needs
to be cut. Do not use any form of blade as you are almost certain to
damage the surrounding tracks, use a pair of wire cutters. H there is
no link present then no further action is required and you may proceed
to the next stage.
Fitting for all iSBue boards
After performing the modifications (if necessary) to link S9 the next
step is to fit the parts comprising of the 1.54T DDFS kit. These are
itemised below
2 off 7438, 74LS38 or 7437
1 off DDFS 1.54T EPROM
2 off wire links
1 off DDFS motherboard