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- From: akcs.n2kyw@hpcvbbs.cv.hp.com (Paul Smith)
- Date: Sun, 26 Jul 1992 20:40:02 GMT
- Subject: How to open your hp48
- Message-ID: <2a730720.1487comp.sys.hp48@hpcvbbs.cv.hp.com>
- Path: sparky!uunet!darwin.sura.net!mips!sdd.hp.com!hp-cv!hp-pcd!hpcvra!rnews!hpcvbbs!akcs.n2kyw
- Newsgroups: comp.sys.hp48
- Keywords: passkey keyboard rclkeys stokeys hokey smokey
- Lines: 172
-
- 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
-
-