Posts: 301
Threads: 28
Joined: Jan 2005
If it is an old one, the keyboard is connected to the main board with a contact near the upper right rubber foot (back view). For "old" I mean serial number < 24xxxxxxxx (earlier than 1984) I think.
The keyboard is "divided" this way:
1 2 3 4 5 5 4 3 2 1
1 [ A ]-[ B ]-[ C ]-[ D ]-[ E ] [CHS]-[ 7 ]-[ 8 ]-[ 9 ]-[ / ] 8
2 [SST]-[GTO]-[SIN]-[COS ]-[TAN] [EEX]-[ 4 ]-[ 5 ]-[ 6 ]-[ x ] 7
3 [R/S]-[GSB]-[ Rv]-[X<>Y]-[ <-] [ EN]-[ 1 ]-[ 2 ]-[ 3 ]-[ - ] 6
4 [ON ]-[ f ]-[ g ]-[STO ]-[RCL] [TER]-[ 0 ]-[ . ]-[SIG]-[ + ] 5
The numbers are the matrix rows and columns and the '-' shows the keys that are in the same row. For the "simptom" that was described it shows a bad contact on the first row of the scan matrix.
This is really a "simptom" of the earlier ones that have the keyboard PCB separated of the main flexible PCB.
If if was disassembled once it can be assembled without the proper "pressure" on the screws (not too "heavy" to avoid broken the plastics!)
Please see on this picture here from the Museum on the top right corner, is the junction of the two parts.
I hope it can help!
Best regards
Nelson