HP-67 display trouble: Help!


Hi everybody,

After a successful card reader gummy wheel replacement, sometimes the display shows a very brilliant row of " --------------" (middle segment) when I turn on the machine.

Even if the calculator is off, when I push some keys, a dull red middle segment twinkles (-). ¿How can I do? ¿How can I fix this problem?

Thanks in advance,



The 'g' segment (the one in the middle, used for the -ve sign) has a separate current control circuit, which is pair of transistors in the corner of the logic board. That, in turn is controlled by a resistor on the keyboard/display board.

Bad contacts between the keyboard/display and the logic board can cause this. Since you've just taken the machine apart to repair the reader, I would check the pins between the 2 boards carefully.


Many thanks Tony,

There was a bad contact between the power plug-in and the display PCB (the ground wire). Now, the machine works fine.


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