dead row of keys hp-15c


I picked up a 15c at a sale today. I put batteries in it and it passed the self test (on-X). But the keypad test fails. The row of keys in the upper left "A B C D E" click ok, but don't enter data. Everything else seems to be fine.

I'm wonder if I should open it up and see if there's anything I can do? Maybe there's a speck of dirt in the wrong place?



A mild rap on the side... and the keys start working.
There must be some dirt floating around in there.

It's all working now!

p.s. I don't recommend this as a repair technique.


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



Thank you very much.
It seems to be working ok now, but if it
starts acting up again I may have to open it up.


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