Some buttons are not working on 42S calculator; how to open case

[baskervi]

I've had this calculator for many years, and this week a handful of buttons quit working. I was going to pick another one up on eBay, but some are going for over $400! What the heck? I figured if I can pop it apart and clean the contacts, it will be as good as new. I can't figure out how to split the case open. Does anyone have any pointers? Thanks

[HP-MACH]

Hi!, baskervi:

Welcome, to Forum!.

If not have, any HP Technical Representative, for repair, or clean ... please, read carefully before ...

Open up the HP-42s: 
Pioneer calculators are held together by eight “heat stakes” – plastic poles that are molded into one half of the case, fit into holes in the other half, and are melted into mushroom, rivet-head shapes to effect a mechanical bond. The top four “rivet heads” are visible, recessed in holes beneath the battery compartment cover. These are accessible and easily undone. The lower four are arranged in a line, beneath and between the lowest two rows of keypads. The mushroomed heads are hidden behind the metal foil on the calculator face. These are inaccessible, but that turns out not to matter much.

Remove the battery compartment door and the batteries. Use a small (3/16” or so) sharp drill bit to cut out the melted tops from the four visible heat stakes that hold the top end of the calculator together. (I put drill bit in a pin vise or other holder and rotate it by hand.)
Caution: You only need to remove 1/16” of plastic or less, so don’t use a power drill, as it will rapidly cut right on through the calculator front!

Once the top end is freed, you should be able to easily pry the front and back apart at the top end, using your fingernails in the slot that runs down both sides of the case. (Don’t use a screwdriver or other prying implement – you’ll mar the finish on the sides of your calculator, and risk internal damage as well.)

As the case starts coming apart, I simply keep prying with my (fairly strong) fingers. It’s a bit of a struggle, but there are only the four hidden heat stakes holding the two halves together. With the right amount of force, carefully applied, they quickly pop one after the other in a zipper-like noise, and the calculator case comes apart.

Caution: Try to grip and pry the plastic case parts only. Don’t get your fingers into the electronics, and don’t bend the printed circuit board. If you apply pressure only to the case halves, the PCB is free and unstressed, and will not be damaged. Don’t use any prying device, as (again) you risk cosmetic and internal damage to the calculator.

[pin224466]

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@miguel Angel Caporalini wrote:

Hi!, baskervi:

Welcome, to Forum!.

If not have, any HP Technical Representative, for repair, or clean ... please, read carefully before ...

Open up the HP-42s: 
Pioneer calculators are held together by eight “heat stakes” – plastic poles that are molded into one half of the case, fit into holes in the other half, and are melted into mushroom, rivet-head shapes to effect a mechanical bond. The top four “rivet heads” are visible, recessed in holes beneath the battery compartment cover. These are accessible and easily undone. The lower four are arranged in a line, beneath and between the lowest two rows of keypads. The mushroomed heads are hidden behind the metal foil on the calculator face. These are inaccessible, but that turns out not to matter much.

Remove the battery compartment door and the batteries. Use a small (3/16” or so) sharp drill bit to cut out the melted tops from the four visible heat stakes that hold the top end of the calculator together. (I put drill bit in a pin vise or other holder and rotate it by hand.)
Caution: You only need to remove 1/16” of plastic or less, so don’t use a power drill, as it will rapidly cut right on through the calculator front!

Once the top end is freed, you should be able to easily pry the front and back apart at the top end, using your fingernails in the slot that runs down both sides of the case. (Don’t use a screwdriver or other prying implement – you’ll mar the finish on the sides of your calculator, and risk internal damage as well.)

As the case starts coming apart, I simply keep prying with my (fairly strong) fingers. It’s a bit of a struggle, but there are only the four hidden heat stakes holding the two halves together. With the right amount of force, carefully applied, they quickly pop one after the other in a zipper-like noise, and the calculator case comes apart.

Caution: Try to grip and pry the plastic case parts only. Don’t get your fingers into the electronics, and don’t bend the printed circuit board. If you apply pressure only to the case halves, the PCB is free and unstressed, and will not be damaged. Don’t use any prying device, as (again) you risk cosmetic and internal damage to the calculator.

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please refer to the following forum posts for the original authors of the material to access a 42S calculator:

this is posted by Paul Broger

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=5

this is another article posted by Paul Broger that also details the opening of the case

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=199

finally,

refer to the following forum post... there are links for internal pictures of the 42S

http://www.hpmuseum.org/hp42s.htm

give credit where credit is due... to the original posters of the information !

[HP-MACH]

Hi!, baskervi:

The other site, with pictures, but, for only open, is ... http://www.finetune.co.jp/~lyuka/interests/calc/hp42s/

[BartdB]

> but some are going for over $400! What the heck?

Don't trust the first price you see. There are always some exploiters, and bidding wars. Be patient & look around.

[RRoss]

Once you have the case open, your problem is likely the foam compression on the Zebra strips from the keyboard that run under the top in front of the PCB and not directly accessable.   Tightening down on the clips (or inserting some thin plastic under them) instead of taking the PCB board off is probably your best solution.  If you twist or turn the clips, they are likely to break.  Once broken they cannot be repaired and you will need to find some other way to attach the PCB board to the keyboard. 

Before you dissassemble you can check this repair out.  Press on the bezzel below the LCD screen (continous pressure) and see if the keyboard now works.  If it does, your problem is worn out foam or lack of pressure by the foam on the connections of the keyboard to the PCB. 

Opening your Hp42s isn't hard, but it aint easy either.  Before you open your Hp42s (and perhaps render it useless), you can still sell it as is.  Why would I suggest that?  Because you can probalby get $30-50 AS IS. 

That would be enough to buy an Hp35s or maybe a used Hp17Bii (which is very similar to an Hp 42s aside from NO TRIG).  Actually has Stat functions and a very easy to use solver.  The newer Hp17Bii+ also has four times as much RAM. 

If you like the pioneer quality, you can buy an Hp32sii for around $100 (usually about half the price of an HP 42s).  Doesn't have any real amount of memory, but is a decent calculator. 

If you use the advanced functions of the Hp42s and want/need a pocket calculator, there is NO substitute.  If you don't need it to be small, an Hp48G can be purchased for around $50 in good shape.  Has the same feel of an Hp 42s aside from its a bigger calculator.  Actually it is better than an Hp 42s for nearly everything but travel.  You can buy a new Hp 50 G for around $100, and it will be fast, but it won't feel nearly as nice as an older Hp (although the Hp 48G is sluggish and actually slow as a graphing calculator).  However, it has a great units conversion library and other features that I do appreciate over my Hp 42s.

I personally travel with an Hp 32sii as to not risk losing my Hp42s (that I opened to add 32K of RAM to).  I find that the Hp 32sii is a nice knock around calculator.  An Hp 35s is the Hp32sii with 32 K of ram, but a messed up HEX, BIN conversion routine and R-P taken off the keyboard.  It gets you a lot closer to the cabability of an Hp42s than the older Hp32sii.  However, it is still worthless to work with matrices and complex number support sucks in comparision.  HEX, BIN support is poorly implemented.  Programming is limited to single charactor varibles.  As I said, if you don't need trig or some of these other features, the Hp 17Bii could be a better alternative (ie you need stats and special functions that don't rely on trig functions).  The HP 17Bii is also a good source of repair parts for the Hp42s if you find the keyboard is truley bad due to liquids or such.  The older Hp 17B uses the same parts, the only differenc are the keyboard legends, ROM and the quartz clock.

[Hodge8]

Hi Ron,

I much appreciated your reply.

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@Ron Ross wrote:

Before you dissassemble you can check this repair out.  Press on the bezzel below the LCD screen (continous pressure) and see if the keyboard now works.  If it does, your problem is worn out foam or lack of pressure by the foam on the connections of the keyboard to the PCB. 

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After hours of fiddling around with other possible solutions, this worked immediately for me, and my 42S is back in business (though somewhat restricted in operational flexibility; ie keeping a finger pressed on the bezel).

Thank you.

Has anyone any ideas for a fix which does not include opening up the 42S?

[HP-MACH]

Hi!, Hodge8:

If you do not want to open your HP42S, to try to repair it according to the directions, then I recommend that you download the emulators, according to your need, form ... http://thomasokken.com/free42/

[Hodge8]

I have an HP42s emulator and it is excellent.

Meanwhile I have a kludge fix for the problem (see attachment).

As you can immediately see, it is merely a plastic wrap securing a block of cardboard (11 mm high) tight on the bezel.

Up to now ( three days), it works!