The Museum of HP Calculators

HP Articles Forum

[Return to the Index ]
[ Previous | Next ]

HP48 Disassembly (from the back)

Posted by David Fenyes on 18 Feb 2001, 3:00 p.m.

I noticed the comment in the HP Museum disassembly notes, that you can't disassemble the 48's without serious damage. I posted this to comp.sys.hp48 a while back (1995 according to Adrian Drury), and thought I'd repost it, with a couple of extra observations. Adrian Drury took pictures as he disassembled his '48 based on these instructions, and has made an excellent web page, which I recommend you visit:

This article does contain some useful points not mentioned in the web page, most importantly how to secure the top of the calculator with small plastic bolts (Thanks to Nick Zacharopoulos).



Hello fellow HP48 owners :-)

If you have a 48S/G, you may have thought about expanding your memory. If you refrained because you didn't want to uglify your calculator, now you have no excuse. I bought two 48S's from EduCalc, and disassembled the first one according to Paul Smith's article (thanks for your bravery, Paul:-) I managed to get it back together, using epoxy to secure the faceplate down with a minimum of wrinkling. My first new 288K calc is quite usable, but looks like an old battle implement (at least a little beat up :-). It's safe to say that a calculator disassembled this way will never be the same again. I wanted calc#2 to be prettier. It turns out that it's relatively easy to make cuts in places not normally visible (behind the red IR port lens & in the battery compartment) to render the front and back halves separable. The benefits of this approach are that your 48 still looks like new, and the structural columns can be salvaged to retain the solid "HP" feel of the new calc. I've written up the directions below.

Disclaimer: The directions are based on MY 2 HP48S's, and may not apply to any others in the world. I'm providing this info so that someone (maybe you) may benefit from it. I can't be responsible for any damage you inflict on anything (including yourself) by following these directions. I also can't guarantee the accuracy of my descriptions. Please THINK about what you're doing to make sure it's not obviously insane (loosening the LCD with a hammer, etc.) You will void your warranty if you take apart the calculator.

Disclaimer softener: This worked for me :-) If you follow directions, you and your 48 should be OK. Also, this is a very long post describing a very simple procedure. Don't be discouraged by the length. The detail is there to help prevent you from goofing :-)

Good luck, and enjoy!

David. -- David Fenyes


Tools & Materials

Feel free to improvise. I used:

1) an X-acto knife, preferably with a #6 blade (thin, narrow trapezoidal blade with a shallow angle -->

                  ______            / <-  sharp!
                 (______)  ________/  
The blade should fit nicely in those keyboard template slots at the ON, ENTER, MTH, NXT, <-, and + keys.

2) A broad, blunt, thin blade, such as the screwdriver on a Victorinox-brand swiss army knife. A butterknife may work. Using a narrow, thick screwdriver will leave ugly marks in the soft plastic.

3) A drill with a very small bit, or a 1/4" bit.

4) The slick backing paper from a sticker

5) a couple of butter knives, Q-tip stems, or wooden matchsticks.

6) Some 14 Ga solid copper wire (I used laquered magnet wire).


Top - toward the IR lens/serial port connector. Bottom - toward the "ON 0 . SPC +" row of keys Back - toward the battery-compartment side of the calc. Front - the faceplate side of the calc.



Instead of ripping off the tin faceplate and destroying the rivet heads, you will make well placed incisions behind the IR lens and in the battery compartment to defeat the 10 plastic rivets. The abbreviated plan is:

1) empty battery compartment and remove IR lens.

2) make 2 holes in the recess behind the IR lens in order to gain access to the 4 rivets above the display, and slice through them.

3) Enlarge the hole behind the (+) battery terminal, and slice the exposed plastic rivet. Make a corresponding hole and slice the corresponding rivet on the right side of the compartment.

4) Dig out the bases of the remaining four rivets beneath the bottom battery-separator ridge in the compartment.

5) Separate the two halves of the calculator.

6) "repair" the plastic rivets to restore structural integrity.

Detailed Instructions:


0) back up your memory and turn the calculator off.

1) Remove the battery case cover and batteries. Carefully peel off the foam pads/battery connectors from the battery compartment and stick them on the piece of sticker backing.

2) Remove the dark red plastic IR port cover:

- Turn the calc back facing you, wedge the dull blade between the IR lens and the calc body about 1cm from the left edge and pry the lens off. Repeat for the right side. The lens will pop out unharmed. (Or you can use your fingernails to pull the lens off for minimal risk of blemishes)

3) Begin the "plastic surgery":

- Look into the recess behind the IR lens:

        |                                                    |
        |______________________________________________      |
   #1--------> |----- |. . . .|     / /\ /\  \  ----- | <-------#2
        |      |      \_______/    /  \/ \/   \       |      |
       	\       				            /
	 \      				           /

I have drawn the IR and serial ports, and the two slots you will need to make. Look into the serial connector and note the level of the PCB. Using the X-acto knife, make a 1cm horizontal score (#1) about halfway between the level of the serial pins and the PCB.

Use a drill with a very small bit (~1mm) to make a row of holes along the scored line. *REMEMBER* where the PCB is, and be sure to angle the drill very slightly downward. If you do this, you will be drilling into air, and will not harm anything of consequence inside the case. Using the X-acto blade, connect the holes to make a slot. If you can't see very well inside the slot, have faith. Stick the X-acto blade into the slot, angled slightly down (away from the PCB), and slice anything you encounter. You should be able to move the blade freely in the slot. To a casual observer, you will look as if you are lobotomizing your calculator. In fact your blade will only hit the 2 plastic rivet bodies behind the slot (and air).

Repeat the procedure to make a symmetrical slot on the other side (position #2) next to the IR port. make it the same width and level as the first slot. Again, you will be drilling and slicing into air if you keep the angle slightly down.

** Alternative: Your task may be considerably simpler if instead of making slots, you use a 1/4" bit to drill holes slightly below the slots indicated above (angled downward, of course,) to give yourself a good view of the rivets before you cut them.

Bravo :-) You have accomplished the scariest part. You should now be able to pry the top of the calculator apart very slightly.

4) Slice the two rivets at the top edge of the battery compartment:

Use the following schematic for the next two sections. Remember, it's ASCII art, so don't measure it with a ruler :-). Read the text for specifics:

                      Battery Compartment

X TOP X ****-----------------------------**** #### | #### | top section ridge 1 -> ------------------------------------+ | | **** **** **** **** middle section ridge 2 -> **X*-------*X**--------**X*------*X** | #### | #### bottom section +-----------------------------------+ BOTTOM (-)

X = plastic rivet # = the hole is already there. * = you make the hole.

Turn the calculator so its back is facing you. Bend the (+) batery terminal (the one in the top left corner of the compartment) so that it sticks straight up and is flat against the left side of the compartment. This will expose a rectangular hole in the top side of the compartment. Using the blade, slice upward along the edges of the hole and across to extend the hole about 3-4 mm toward the rear of the calculator.

The hole is now a window into the calc innards. Look into the window at a shallow angle. You will see a plastic rivet. This is the rivet amidst the "[6] [X] [9] [/]" keys. You can slice this easily with the blade.

Now you need to make an identical window in the top right corner of the case and slice through the second rivet (the "[Lshift] [Alpha] [4] [7]" rivet.)

5) Free the remaining four rivets from their bases:

The battery compartment is divided into three sections by two ridges. The four remaining rivets are behind the bottom ridge, very slightly toward the middle section. They lie amidst the following keys:

	"{1} {ON} {0} {Rshift}"
        "{1} {2} {0} {.}" 
        "{2} {3} {.} {SPC}" 
        "{3} {-} {SPC} {+}"
You will harm nothing by digging around, but you want to damage as little of the compartment as possible. Start slicing out sections of the bottom ridge using the keys as a guide for the horizontal dig sites along the ridge. Actually, the "+" signs on the bottom and middle battery icons accurately indicate the positions of the middle two rivets. When you encounter a small (~14Ga) circular hole, you have identified a rivet. You need to free each rivet from the surrounding plastic so that it wobbles freely.

HINT: Since you'll be doing lots of digging, you may try to use the edges of the battery case for leverage. If you line the externally visible outline of the compartment with masking tape, you'll prevent cosmetic damage.

6) Separate the two halves of the case:

Now the calculator's keyboard should be facing you. Insert the blade in the keyboard-template slot near the NXT key. The blade should go straight back to the back half of the calc. Apply pressure on the handle toward the midline of the calc. This will disengage the front half from the back half. With the screwdriver blade, gently pry the halves apart at the [F] key. Place something (like a butterknife) between the halves to keep them apart. Repeat the procedure at the [MTH] key (pry near [A]), the [ENTER] key (pry near [SIN]), and the [backspace] key (pry near [1/x]). The whole top part of the calculator should be nicely separated. The bottom 3 hooks are somewhat more resistant to separation, probably because of their close proximity to one another. The best thing to do here is insert the blunt blade (victorinox screwdriver or butter knife) between the two halves near the [-] key. Pull the handle up toward yourself. The bottom half should disengage from the top half. Stick something (like the butterknife or wooden matchstick) between the halves to keep them apart. Repeat this now at the bottom of the calc (the "." key) The calculator should completely come apart now.

7) Putting it back together.

You could probably just snap the two halves together. However, if you want a little more stability, it is possible to restore the structural function of the rivets.

The rivets are hollow. Using the X-acto blade, clean up the ends of the rivets on both halves of the calculator. The hollow center of each rivet should be round and free of plastic debris. You may also wish to clean up your hacking near the IR port and in the battery compartment.

14 Ga laquered solid wire fits snugly in the hollow rivet bodies. Cut six straight pieces of the solid wire, exactly 1cm each. Make sure that the ends of each piece fit neatly into both halves of the top six plastic rivets (you won't need to restore the four bottom rivets that you freed from their bases.) Push the wire pieces into the top six rivet bodies in the back half of the calculator.

Bend the (+) battery terminal back into shape. Align the front half of the calculator carefully with the back half. The rivet remnants on the front half should align with the wire pieces sticking up from the bottom half. The (+) and (-) battery terminals should fit through their respective slots, and the top half should rest flat on the bottom half. Press the calculator together starting at the bottom. The pieces should snap together with no difficulty. If the rivets and wire are misaligned, you may need to push the wire into alignment with a needle. Remove the two foam-backed battery terminals from the sticker-backing and replace them in the compartment. Replace the batteries and battery compartment cover. Snap the IR lens back into place.

Congratulations! You have disassembled (and hopefully upgraded :-) your calculator without ruining its appearance :-) If you were careful, it should look brand-new!

Edited: 20 July 2003, 5:32 p.m.


[ Return to the Message Index ]

Go back to the main exhibit hall