Acorn Computers Limited BBC A Hardware Manual
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Contents
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44Depending on the particular links that are to be modified it may be necessary to remove the keyboard inorder to gain access. Links S4, 58, S10, S14, S17, S18, and S30 are those in question on boards up toissue 3. Boards from issue 4 onwards also have links S35, S36, S37 and S38 beneath the keyboard.At this stage one must consider the particular links that are to be modified. Table 4.1 at the end of thissection specifies whether a particular link is soldered wire, copper track or a jumper.If any of the soldered wire links are to be modified then the main PCB may have to be removed from thebase to allow access to the underside of the PCB.4.1 Keyboard PCB Removal.The keyboard assembly can be detached by removing the two nuts and bolts situated on either side ofthe keyboard PCB (please note that some main PCB's prior to issue 4 have two keyboard securing boltson the left hand side of the keyboard PCB). The location of these bolts can be seen from the photographsin chapter 5. The next step in removing the keyboard assembly is to carefully unplug the interconnectingribbon cable from the main PCB (PL13) and also the loudspeaker connector from PL15.The keyboard can now be safely set aside to reveal the main PCB beneath.4.2 Removing the Main PCB.Before the main PCB can be removed the two wires from the BNC "video out" socket on the rear of thecase must be disconnected. On early issue boards these two wires were soldered but some later issuesuse push fit connectors. It is important to note which of the two wires is the signal wire and which is theground wire, so that they can be replaced correctly. It is suggested that the ground wire be marked byplacing a piece of coloured insulating sleeving over the wire. On some late issue boards black (0V) andred (signal) wires are fitted as standard.The next step is to remove each of the seven power supply cables from the main PCB. It is important totake care when removing these cables as a reasonable amount of force may be required. It is particularlyimportant not to bend the flat PCB pins backwards and forwards because they can easily fracture. |
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