Changing display contrast on HP 27s


Hi everyone, I'm new to this forum. I've lost the manual for my HP 27s calculator so maybe someone can help me here. I want to change the contrast of the LCD display on my calculator, I know this is possible but I've forgotten how to do it. Can anyone help? Thanks!


Mitch --

As with all Pioneer-series models: While holding down clear ("CLR"), press "+" repeatedly to darken the pixels; press "-" repeatedly to lighten the pixels.

Less well-known: Turn the calc off while holding down "1/x" and "+" simultaneously to put the calc into a battery-conserving "coma" that stops the clock. Memory contents will be unaffected; "MACHINE RESET" will be displayed upon powering on.

-- KS

Edited: 3 Jan 2008, 3:23 p.m.



You seem to be pretty knowledgeable about the 27s. Maybe you can explain this:

Just a few days ago, I was sitting in a meeting with a client, and grabbed my 27s for a quick calculation. Turned it on, did a few calcs, then it spontaneously BEEPed and displayed "Machine Reset". I discovered that the display setting (FIX) was gone, but all my equations and variable values were intact.

What happened? Anyone else had a similar experience?



Karl, thanks very much!! BTW what's the advantage of putting the calc into "coma" mode? And how do you get it out of this mode when you turn it on again?



Martin and Mitch --

I'm not sure why Martin's HP-27S reset itself (low batt, perhaps?); the reset will retain memory contents, and change settings (including display contrast) to default values.

The only advantage to "coma" mode is battery conservation. The clock cannot be turned off otherwise, and its constant running will discharge the expensive cells significantly faster (at $10 for a set of three quality Silver Oxide cells). Of course, if you use the time-based functions, then it's best to turn it off normally.

Simply turning the calc back on will awaken it from "coma" mode, with a Machine Reset.

All of the above also applies to the HP-17B, HP-17BII, and HP-42S, except that the latter has no time clock.

-- KS

Edited: 3 Jan 2008, 11:55 p.m.


OK I just tried pressing the "+" (bottom right) and "1/x" (top right) keys simultaneously, then I power off and on and MACHINE RESET isn't displayed. What am I doing wrong?

It would be nice to save on batteries...




It worked for me, but I pressed the 1/x key first, which caused a beep, then the + key, then the CLR key while holding the other two.


Ah, didn't realize I had to keep holding down the 1/x and + keys when I press the CLR key...thanks!


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