Newsgroups: comp.sys.hp48
Keywords: passkey keyboard rclkeys stokeys hokey smokey

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

Newsgroups: comp.sys.hp48