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Interesting little Pioneer keyboard repair
10-08-2017, 02:15 AM (This post was last modified: 10-08-2017 02:15 AM by mfleming.)
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Interesting little Pioneer keyboard repair

I thought some might be interested in a repair I did recently on an HP Pioneer calculator keyboard. It's unlikely anyone will need to do the same, but I'll add it to the MoHPC knowledge base all the same.

I recently acquired an HP-27S calculator and manual for about a quarter of the going price on TAS. Although the seller stated the calculator no longer worked, I thought maybe it had the usual keyboard contact failure, which can be repaired without too much trouble. I was also most interested in the manual since I didn't have one for my working 27S. Seemed like a good gamble so I bought it.

Unfortunately as you can see from the photo collage below, the Power On key had been permanently damaged. You can see in the upper left hand picture the pry marks made by a knife or screwdriver blade. I didn't notice the marking in the photos - my fault for not examining them with more care. But, like I said, I was happy to get the manual.

[Image: uc?export=view&id=0Bwt5Q_LizRq6YlNJNElOb2h4LWc]

After opening the case and trying to fix the usual ribbon contact fault without success I decided to trace the two power button contacts to a convenient point and solder in some wires to close the power button remotely. You can see the wires in the lower left photo, with tape used for strain relief. I reassembled the CPU board, closed the case and verified the calculator would power up when the wires were touched together.

The lower right hand photo of the calculator display confirms that I was on the right track. Now that I knew the calculator worked, how was I to put it back into service? I looked at forum posts on how to disassemble and repair the keyboard. After reading the various descriptions and considering that approach, I thought "Only with a gun to my head." An alternative was to transplant the CPU board to an HP-17Bii donor and transfer the faceplate, but there would be four mismatching keys. Not a bad approach, but it would be labor intensive and look like a noticeable hack.

I finally settled on the solution you see in the last, upper right hand photo. I drilled and then squared off a hole for a small pushbutton switch, soldered the wires to it and closed everything up. Voila, another HP calculator returned to active duty.

Now some may find an algebraic calculator, even an HP one, to be somewhat objectionable. Consider what the 27S provides though. Pretty much the full 17Bii capability including HP Solver, TVM, 1 & 2 variable statistics, probability and a real time clock & calendar with appointments. Add in a pretty decent set of scientific functions including hyperbolics, base arithmetic and conversions and you have a pretty nice pocket companion. It can even print. What's not to like?

It is a little weird having the On button in the diagonally opposite corner, but you get used to it!


BTW, I understand the 27S and 42S use the same PCB. Any chance adding a second SRAM trick will work for the 27S?

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Interesting little Pioneer keyboard repair - mfleming - 10-08-2017 02:15 AM

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