Hello David,
You need to check all of the connection pins on all of the boards
starting with the power supply unit and working your way through them
for dry joints (cold joints USA) only resolder these if you can solder
correctly, they need to be desoldered cleaned and resoldered. What you
are looking for is cracking around the solder around the pins. More than
likely this will be the couse of your number 7 not working, check the
connections on the back of the number 7 switch, the connection pins on
the keyboard and most inportantly the connection on the top and bottom
connections of the pricing board.
Regards
Alan
Alan Hood
ami-man
UK
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Alan Hood