abrir hp48

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How to Open Your HP48 
Here are illustrated instructions about how to open your HP48. I had always wanted to try 
opening mine, but the thought of peeling off the face plate really didn't appeal to me. So, 
when I saw the great instructions about how to open the calculator from the back, by David 
Fenyes, I knew it was time to take the plunge! I spent a day over Christmas break (1995) 
opening the case, and I've been very pleased with how it turned out. 
Since this is a constant topic on comp.sys.hp48, I thought I'd take some pictures of my 
calculator to show how to open it from the back. In fact, one of the things that worried me 
about opening my calculator was the imprecise nature of the text directions. But, with these 
pictures, I hope it will make it easier and less stressful to open your calculator! I'm not 
giving instructions as detailed as the ones available in pure text form, since I think that with 
the pictures, it should be a lot easier to figure out how and what to cut. 
I should note that I took these pictures after I was all done opening my calculator, so some 
pictures may show holes you haven't made yet. Don't worry, just pay attention to the 
directions! 
DISCLAIMER 
I can take no responsibility for any damage done to you, anyone else, or any HP 
calculator as a result of reading, following or attempting to follow these 
directions. Make sure you know what you are doing before, after and while you 
are doing it. Read all the way through this document first! By attempting the 
steps described below, you void your warranty. 
Credits: Thanks to David Fenyes for his excellent instructions about how to open 
the calculator from the back. In many cases, our instructions parallel each other, 
since I'm adding my pictures and ideas to his description. Also, thanks to Sean 
Cier and Mike Sherman for their patience and the use of an SGI, IndyCam and 
SuperVHS camcorder to capture and manipulate these images. 
 
Here's an overview of what you will do to open the calculator. 
1. Back up your data first. Although the calculator should theoretically be 
able to retain memory without batteries for at least two days, back up 
anyway! 
2. Take out the batteries and remove the IR cover from the calculator. 
3. Make access holes behind the IR cover and cut through the four rivets near 
the screen. 
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4. Make two access holes in the battery compartment, one by the plus battery 
terminal and one on the other side of the compartment. Cut through those 
two rivets 
5. Make holes to cut four rivets underneath the bottom "ridge" in the battery 
compartment. 
6. Take apart the two halves of your calculator! 
 
Here are some tools and supplies you will need. 
1. An X-acto knife with a good sharp blade. Sharper is better. David Fenyes 
suggests a number six blade, though others will work well. 
2. A wide, flat, thin blade of some sort. This will be used to pry on the case, 
so the wider and thinner and blunter the better. Otherwise, the plastic the 
case is made of may be "dented". 
3. A drill with a small bit, anywhere from one quarter inch (5mm) to one 
sixteenth inch (2mm). I used a drill press, which made the work much 
easier because of the extra control I had over the motion of the drill bit. 
Obviously, not everybody will be able to use a drill press, but if you can it 
may make your job easier. 
4. The slick backing paper from a sticker. 
5. You might want long, thin pieces of metal to spring the metal clips that 
hold the two halves of the calculator together. I used some stiff pieces of 
spring steel. Alternatively, you can use a thin bladed screw driver. 
6. Matchsticks or similar size pieces of material to hold the pieces of the case 
apart as you separate it in the last step. 
7. If you want to "restore" the structural integrity of the plastic rivets, you 
will need about four and one quarter inches (10cm) of fourteen gauge 
copper wire. It should not have any plastic insulation on it. 
8. Good light. This is a must, especially for looking into the mysterious inner 
recesses of your calculator. A bright desk lamp is fine. 
 
Here are the main instructions. 
1. Back up your data. To do this, you may either back it up via IR onto 
another calculator or use a serial cable connected to your computer. For 
those of you who don't know how to do data transfers, it is explained in 
detail in Chapter 27 of the HP User's Guide included with your calculator. 
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2. Snap off the IR cover at the top end of the calculator. Turn the calculator 
so its back is facing you. Use the wide blade described in number two on 
the tools list to pry gently in the crack where the IR cover and the 
calculator back meet. Pry about half an inch from either end of the IR 
cover. I find a twisting motion works well. That will disengage one (or 
maybe both) of the molded hooks on the back of the IR cover. If you need 
to, repeat the prying process in the other end of the crack. With a little 
care, you probably won't mar the plastic. To avoid any risk of marring the 
plastic, you can try prying off the IR cover with your fingernails, but I've 
found that difficult. 
3. Next, remove the battery compartment cover and three batteries from the 
battery compartment, and do not replace the cover, as you will be working 
in there later. Then peel off the two foam-backed metal contacts in the 
battery compartment and stick them on the piece of slick paper (number 
four on the tools list). Set the battery compartment cover aside with the IR 
cover and the foam-backed battery contacts. 
4. Now that you've done that, you're ready to begin actually cutting into your 
calculator. You need to cut through the four rivets at the screen end of the 
calculator. There are two on each side of the screen. In order to cut them, 
make two holes as shown in the picture below. 
 
The location of the holes is obvious, and you can see the four vertical 
rivets in the holes (They're the circular things). The piece of plastic in 
between the rivets is another structural piece which gets sliced through just 
like each rivet. More will be said about this piece later. To make my 
access holes, I drilled two rows of holes and smoothed the sides with an 
X-acto knife. I decided to make mine big enough so I could see everything 
I was cutting in there. As long as you cut where I did, or slightly lower in 
the picture, you won't hit anything. The important thing is to angle your 
cutting blade down, away from the circuit board, which is attached at the 
top of the rivets. 
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5. Now proceed to the battery compartment. Here's a straight-on shot of what 
mine looks like after I drilled holes to open the case. 
 
The first thing to do is to cut through the two rivets behind each upper 
corner of the battery compartment. Here's a picture of the one on the right. 
 
The rivet is the little knobby thing sticking up in the middle of the picture. 
This is one of the trickiest rivets to cut because of the close quarters. Here, 
you need to make sure you can see what you're doing, because if you drill 
or cut wrong, you can hit the circuit board. So take this one nice and easy. 
Try to cut it relatively high up, maybe even higher than I did in the picture. 
I could
have made a bigger access hole, but I wanted this to be as small 
and neat as possible, so I made my life a little more difficult than 
necessary. Now, do the same thing for the rivet in the corresponding 
position behind the left hand corner of the battery compartment. Sorry this 
picture isn't as clear as the previous one, because the battery clip was bent 
down in front of the hole. 
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To make this hole, bend the positive battery clip until it is pointing straight 
up. Your life will be considerably easier this way, and I doubt if the hole 
could be made if the clip wasn't bent up. To make the access holes for the 
two rivets behind the corners of the battery compartment, I drilled two 
columns of holes vertically along the wall of the compartment, smoothing 
the sides with a X-acto knife. 
6. Now, tackle the four rivets underneath the batteries. Their locations are 
shown clearly in this picture. I'm sorry about how dark it is, but you can 
see exactly where the four rivets are. 
 
To cut these rivets, I'd recommend cutting around them, as I have in the 
picture, and also drilling right down on top of them. Although it may not 
look this way, all four rivets are not connected to any surrounding plastic. 
That's the important part. 
 
 
 
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7. Finally! All ten rivets are sliced, if you did it right. The only change in 
structural integrity you should notice is that you should be able to squeeze 
the two halves of the calculator together slightly if you press the space 
above the screen, where the HP logo is. Also, the two halves can now be 
separated slightly in the same place. If you can't move the two halves at 
the top, here's why. The piece of plastic between the two rivets attaches 
the two halves of the calculator slightly above where you (and I) made the 
cuts in those rivets. So, what you need to do is gently pry at the top end of 
the calculator (the part above the screen) until it pops off the rivets. The 
place that joins the rivets to the calculator appears relatively small, so it 
won't take too much pressure. Or, you can try angling an X-acto knife to 
cut any attachments. The spot I'm describing is shown in a picture near the 
end of this page. 
8. Now for the big step. To physically separate the two halves of the 
calculator, you need to pry the two halves apart by inserting a small, flat 
screwdriver blade or spring steel (numbers two or five in the list of tools) 
in the slots down each side of the keyboard. The slots are located by the 
[MTH ]key, the [NXT] key, the [ENTER] key, the [backspace] key, the 
[rightshift] key and the [minus] key. Yes, you do need to fit something 
down those slots! The trick to opening the case is that there are seven 
metal clips that hold the case together. They are located near each of the 
slots at the edge of the keypad, with the exception of one located at the 
bottom end of the keypad, near the [decimal point] key. The clips are on 
the top half of the calculator, and they face out and up. They lock under 
ears on the bottom half of the case, which stick toward the center of the 
calculator. To separate the two halves, you need to insert a blade into each 
slot so it gets down past the top half, then pry the bottom half out, pushing 
the top part of the blade you're using towards the center of the calculator. 
You can use the matchstick pieces to hold the calculator halves apart, but I 
found they weren't necessary. Before you start prying, you need to make 
sure that the positive battery contact is not hooked on the edge of the 
battery compartment. It has a hole in it that hooks on a "ear" on the edge of 
the compartment, and if that's hooked, the two halves won't come apart. It 
has a tendancy to spring back into place all by itself, so check it 
periodically as you open the case. To open the case, I first pried by the 
[NXT]key, as shown here. I also used spring steel to do the prying, not a 
screw driver, so I don't know how well a screw driver would work. 
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Then, I pried by the [MTH] key. 
 
Then, I pried by the [backspace] and [ENTER] keys. 
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Those four clips were the easy part. I know of no easy way to describe 
how to get the remaining three, so take a look at the following two 
pictures. This one shows one of the metal clips up close. The dark green 
part underneath the metal clip is the top edge of the calculator (the circuit 
board was upside down for this picture). 
 
This one shows the locations of the three metal clips down the side of the 
calculator. They're the light rectangles just above the dark green edge of 
the calculator. One is all the way down at the left end of the picture, one is 
just to the right of center, and the third one is one quarter of the way in 
from the right hand of the picture. 
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I should also mention that the keyboard is at the left-hand end of the 
picture, facing down, and the screen is at the right-hand end of the picture, 
facing down. 
 
Basically the only thing you can do is pry in the slots by the [rightshift] 
and [minus] keys. But two of the last three clips aren't exactly under those 
slots, as they were with the previous four. Those two take some more 
careful work. These also require you to pry a little harder than you did for 
the previous four. As you try to get these three clips separated, keep gently 
twisting the two halves of the calculator. When you get one clip popped 
off, you will be able to carefully swivel the two halves of the calculator 
apart, with some more careful twisting and coaxing! Then this is what you 
will see - the front and back halves of the calculator! 
 
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9. Now, here are some other shots of the circuit board of the calculator, for 
those of you who are interested. This one is a close up of the area where 
the memory expansion is done. The shiny metal area below is under the 
battery compartment when the calculator is held upside down. In this 
picture, you can also see the locations of the six rivets at this end of the 
calculator (The hollow tubes). As you can see, you need to be careful of 
the circuit board when you're cutting through the rivets behind the corners 
of the battery compartment! 
 
The RAM chip is the smaller chip on the left. The gold pads in a row 
above it are the connectors for the expansion slots on the GX. Pin 1 is at 
the right in this picture. When I have some more time, I'll do a page about 
how to expand the RAM. For now, this is all you get :-) I believe the 
74HC00 goes on the 14 pads on the right side of the PCB. The other 14 
pads, to the left of the RAM, are for the 74HC174 which does address line 
decoding to enable the 32 banks of RAM the GX can address. 
10. And, for those of you interested in the IR end of things, here's a view of 
the other end of the calculator. 
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Although I haven't verified this, I believe this picture covers enough area 
to be helpful to people who want to upgrade the IR. If
I do an IR upgrade, 
I'll do a page about it, but don't ask me about IR upgrades, because I don't 
know exactly what to do. 
11. This is a closeup view of the four rivets you chopped through near the 
screen of the calculator. By the way, the processor is the large chip in the 
middle. 
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If you look carefully, you can see that the rectangular piece of plastic 
between the two rivets was attached to something, and that the plastic has 
been slightly "sheared" off. That's what I was referring to previously, so if 
the top end of your calculator doesn't pry apart, look where my rectangular 
piece was attached and use a little imagination to figure out where it goes 
inside the calculator :-) 
12. Now, you can put it back together. First, clean up the surfaces of the rivets 
you cut through. If you want to, you can cut lengths of the 14 gauge wire 
and insert them in the hollow rivet centers. David Fenyes recommended 
1cm. long pieces, but I didn't find them necessary. When you snap the case 
back together, line up the ten pieces of wire sticking out of the rivets with 
the holes in the rivets in the other half of the calculator. Snap the two 
halves together in the reverse order you took them apart, starting by 
snapping together the bottom clips, then working up the sides of the case. 
You should hear clicks as each clip snaps into place. Then, bend the 
positive battery connector back down the way it was. Take the foam-
backed battery contacts off the sticker paper and stick them back where 
they go. Snap the IR cover back on, and you're done! I hope it works! 
Comments are welcome, although I won't guarantee personal responses to 
questions. 
Adrian N. Drury 
mailto:drury@andrew.cmu.edu 
 
 
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