PLUS 4 Troubleshooting                              Page 4


       8) KEYBOARD FAILURES

            A) Check pins on ribbon cable for good connection
               O.K.

            B) Check for shorts - CN5, CN6, FB's, Diodes
               O.K.

            C) Check chip select to U27 and the I.C. U27
               O.K.

            D) Check U1 for proper operation
               O.K.   If not: 1) Check socket
                              2) Check for bad U1


       9) FAILURES IN SOFTWARE MODE - All units should be checked for
          proper operation, when any repairs are necessary.
          To Check: 1) Press 'F1' on keyboard
                    2) Press 'Return' to enter Word Processing mode
                    3) Press 'Commodore' key and 'C' key at the sam
                       time
                    4) Type 'tc' and press 'Return' to enter
                       Spreadsheet
                    5) Press 'Commodore' key and 'C' key again
                    6) Type 'tw' to return to Word Processing mode

          Watch for video or loading problems, then:

            A) Check jumpers at J1-J6 for correct connection
               O.K.

            B) Check U1, U2, U25, U26