Commodore PLUS 4 Service Manual page 23

PLUS 4Troubleshooting
8) KEYBOARD FAILURES
A) Check
B) Check
C) Check
D) Check
9) FAILURES IN SOFTWARE MODE -All
proper operation, when any repairs are necessary.
To Check: 1) Press 'Fl' on keyboard
Watch for video or loading problems, then:
A) Check jumpers at JI-J6 for correct connection
B) Check Ul, U2, U25, U26
pins on ribbon cable for good connection
O.K.
••
for shorts -CN5,
O.K.
••
chip select to U27 and the I.C. U27
O.K.
••
Ul for proper operation
If not: 1) Check socket
O.K.
••
2) Press 'Return' to enter Word Processing mode
3) Press 'Commodore' key and
••
tIme
4) Type ltc' and press 'Return' to enter
Spreadsheet
5) Press 'Commodore' key and 'C' key again
6) Type 'tw' to return to Word Processing mode
O.K•
••
CN6, FB's, Diodes
2) Check for bad Ul
units should be checked for
Page 44
'c'
key at the same