HP Forum Archive 08

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HP 67 Display Problem Message #1 Posted by J C Latta on 5 July 2002, 12:18 a.m. I have an HP 67 that works great. Howver the display (the red LED digits) have become dim; significantly so but I can still see them. Does anyone know the source of this problem and can recommend a repair service that can handle fixing this? Thanks.

Re: HP 67 Display Problem Message #2 Posted by David Smith on 5 July 2002, 4:29 p.m., in response to message #1 by J C Latta There is a current source circuit on the CPU card that can affect the display level. It is composed of a matched pair of transistors. Also the ROM0 chip that drives the display anodes is powered through a resistor. The value of this resistor (or the chip itself) also affects the display level. Also the cathode driver chip on the keyboard can affect the display level. Finally the middle horizontal segment of the displays is driven differently than the other segments. A difference in the brightness of this segment vs the others may may be adjusted by varying one of the resistors on the keyboard circuit.

Re: HP 67 Display Problem Message #3 Posted by J C Latta on 6 July 2002, 3:09 a.m., in response to message #2 by David Smith Mr. Smith, I am a finance person, not an engineer. Do you have a reccommdation on someone who can fix this display problem? Thanks. J C Latta

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