From comp.sys.hp48 Wed Aug 5 22:54:49 1992 Path: seq!rock!stanford.edu!rutgers!usc!sdd.hp.com!hp-cv!hp-pcd!hpcvra!rnews!hpcvbbs!akcs.n2kyw From: akcs.n2kyw@hpcvbbs.cv.hp.com (Paul Smith) Newsgroups: comp.sys.hp48 Subject: How to open your hp48 Keywords: passkey keyboard rclkeys stokeys hokey smokey Message-ID: <2a730720.1487comp.sys.hp48@hpcvbbs.cv.hp.com> Date: 26 Jul 92 20:40:02 GMT Lines: 171 Disassembling the hp48sx (may or may not correspond to the 48s, but probably will to some extent) Sufficient numbers of people (more than 1) have requested information on how to disassemble their hp48. Despite the fact that that's pretty scary, I will entail what I know here. Thanks to David Holmes for taking the first step and helping make my attempt more informed. None of the information that follows came from hp, so if what I say starts to sound rather official, it's not. For the few folks out there who've actually had to send their hp48 back to hp for service, you probably ended up with an entirely new unit. I suspect the reason for this, aside from some labor cost savings on the part of hp, is that they really aren't much fun to take apart. You can draw your own conclusions as to why it was designed that way. 0. Backup your memory. You will need to remove the batteries for awhile to disassemble the unit, and you may have them out long enough to cause memory loss (although in my case, even 2 days didn't wipe anything out). 1. Remove the tin key overlay. The overlay is attached with double- sided tape of some sort. A little care and patience will allow you to remove it only slightly warped, and it is fairly easy to straighten out later. I took a small jewelers screwdriver and started prying near the "ON" button, and worked upward toward the screen. When you get near the screen, try to preserve the shape of the overlay because that portion is a bit more difficult to properly straighten later. Once the overlay is removed, put it in a container or somewhere away from dust. The double-sided tape should stay with the overlay (mine did, at least) and will gather dust and stuff making it less sticky if left out in the open. 48sx owners will need to remove the little hp logo insert above the screen as well. 2. Defeat the 10 plastic rivets. Believe it or not, these rivets aren't all that critical to holding the unit together, so you can be as careful or as reckless as you want (I prefer reckless, because I hate plastic rivets). A good way to carefully remove the rivet heads is to use a flat head screwdriver that is the same width as the recessed rivet hole (4mm?) and "drill" the head away by hand with the screwdriver. The head is about 2mm deep, so stop "drilling" there to leave the keyboard material shoulder intact for easier reconnection later. There are 6 rivets near the number keys and four above the screen. These rivets above the screen perform more of a holding function than the others, and you may want to consider using some screws and small washers to replace them when you re-assemble. 3. Separate the lower half from the upper half. The upper half of the calculator contains almost all of the components except for the piezo "beeper" element, and there are no interconnecting wires between halves. The only obstacle is the snap-together "hooks" that David Holmes refers to. These hooks are positioned near the [A], [F], [SIN], [1/x], [ON], [+] and [.] keys (the one by the [.] key is a real bugger!). Refer to the cutaway diagram below for details. Key overlay here ___ \ ____________ \ | | ____________| ______ | | _ | | <--- Upper section. | | | | | ________________| | | |_| | | |___ Circuit board and other | | | components (affixed to | / | <--- Lower section. upper section) |/__ | Has a lip which | | | engages with metal Metal "hook" ---> | / | | "hook" from upper |/ | | section. | | | ________________| | | | | To separate the two sections, you will need to push the lower section out and down around the hooks. You can't do this from the outside because the upper section hangs over the lower, so you have to go from the inside. Luckily, the six slots in the keyboard (used by the separate user-overlays that fit over the original overlay) near the [MTH], [ENTER], [blushift], [NXT], [backspace] and [-], come in handy for this. These slots are not exactly lined up with the hooks, but are close enough. You can insert something in these holes (I used a jewelers screwdriver, flat head) at an angle that is mostly down and somewhat out, to a depth of about 5mm, and come in contact with the lower section. Push the lower section out about 2mm (this will take a bit of force), while wedging something in the outside gap to separate and hold the sections apart while working on the other hook positions ( a wooden matchstick works). I recommend starting with the [A] or [F] positions first, working down whichever side you started with, then do the other side, and leave the [.] position for later (there is no helpful slot there). 4. Remove the battery cover and the batteries. The two battery contacts which come through the case will need to go back through the case when the sections separate. The upper contact is hooked on a plastic boss, and needs to be freed from it. Just pop it off with your finger or a screwdriver. 5. Very carefully pull the two sections apart at the top (above the screen). If you have freed all the hooks, the case should sort of hinge at the bottom edge. This is due to the last hook (near the [.] key). Some careful twisting and working of the sections should free this hook as well. You should now be able to completely separate the two sections. I recommend at this point that you take a pair of pliers and flatten that last hook so that it will not hold next time. It is really not needed anyway, as the other six hooks hold the unit together just fine. Now you can poke around and explore things. Be careful what you touch, I'm not sure how sensitive the insides are to static discharge from your fingers, etc. If you're interested in adding stuff, some open real estate can be found in the areas between the battery compartment and the card receivers, and in the cavities in the lower section below the tin shielding on either side of the card ports (this is where I put some jacks). If you own a 48s, you may find a lot more space. If you want to disassemble the unit further, like removing the circuit board from the upper section, you have a considerably tougher job on your hands, and you're on your own. Also, if you separate the screen from it's circuit board, you will disturb the rubber conductors (there are two) which provide electrical connection to the lcd rows and columns (zebra strips). Upon reassembly of the screen, you may find that you have lost some rows or columns in the display (not permanent, just a zebra strip alignment problem) and will have to keep reassembling and perhaps cleaning until it comes out okay. I haven't done this to my hp (yet) but I have done it to other cheap calculators and it wasn't fun. As to questions about what exactly is inside, I can only guess. David Holmes had some observations, and there are apparently a lot of people out there in netland that know a lot more about the insides already. Reassembly- Putting it back together is much easier. You may need to clean up the remains of the rivet heads so they will easily reinsert into their holes. Make sure the battery connections align with their respective holes, and snap the unit together, applying pressure where the six (or seven, if you left that one near the [.] key alone) hooks are. You will probably want to hold the case together at the top with one or two of the rivets there. If you can find a wood screw with a flat or thin head, you can screw it into the body of the rivet and let the head hold the upper section surface. You may need a small washer for this. A machine screw will probably work as well, but will strip the plastic easier and not hold as well. I have only one screw holding mine together and it works fine. You will probably need to re-shape your tin overlay, as it probably took a beating during removal. I removed the sticky tape from mine, but it's probably better not to (unless it really wont stick anymore). Put wax paper over the tape and put the overlay face down on a hard cover book. Grab a hammer with a smooth and somewhat flat head, and pound away. DONT pound away on the part that surrounds the screen (beveled part). You can probably use your fingers and a little massaging to fix that area. With a little care you can end up with an overlay that looks like new. Press the overlay in place and hope it sticks. If not, a little rubber cement wouldn't hurt. Have fun! Paul Smith v055qmd6@ubvms.cc.buffalo.edu