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| Science Forum Index » Electronics - Repair Forum » HP 38C calculator disassembly?... |
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| Peabody... |
 Posted: Wed Oct 28, 2009 7:03 pm |
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Jeff Liebermann says...
[quote]You're going to have a problem getting the keyboard
section apart. The case comes off easily. Two screws in
the battery compartment and it breaks open. Watch out
for the loose IC's. Take photos if you can't remember
the chip directions.
The keyboard is held together by melted plastic blobs.
Break them off and the keyboard section will come apart,
but good luck getting it back together. You're better
off immersing the entire assembled keyboard in some
alcohol, and hope that the crud will wash away.
Eventually, the alcohol (and water) will evaporate.
[/quote]
I think you are describing the early version of the 38C,
and perhaps other Spice series calculators. At some point HP
switched over to a new design which had all the chips
soldered in the usual way. And that's what I have.
I didn't find the case to come apart easily at all. I ended
up using the dental floss method of getting it apart. That's
from the hpmuseum.org forum. The keyboard on mine has a
metal dome for each key, and all the domes are held in the
right place by a sheet of plastic tape. So I cut through
the tape around the misfiring dome and removed it, cleaned
it, and put it back. It seems to work fine now.
I took pictures of the keyboard and the bottom latch:
http://drop.io/HP38C_KeyRepair |
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| Jeff Liebermann... |
| Posted: Wed Oct 28, 2009 9:05 pm |
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On Wed, 28 Oct 2009 20:03:46 -0500, Peabody
<waybackNO784SPAM44 at (no spam) yahoo.com> wrote:
[quote]Jeff Liebermann says...
You're going to have a problem getting the keyboard
section apart. The case comes off easily. Two screws in
the battery compartment and it breaks open. Watch out
for the loose IC's. Take photos if you can't remember
the chip directions.
The keyboard is held together by melted plastic blobs.
Break them off and the keyboard section will come apart,
but good luck getting it back together. You're better
off immersing the entire assembled keyboard in some
alcohol, and hope that the crud will wash away.
Eventually, the alcohol (and water) will evaporate.
I think you are describing the early version of the 38C,
and perhaps other Spice series calculators. At some point HP
switched over to a new design which had all the chips
soldered in the usual way. And that's what I have.
[/quote]
Sigh. Time to tear one apart. I couldn't find an HP38c in my pile,
but did find three HP38e calculators. I tore one apart and tooks some
photos:
<http://www.11junk.com/pics/hp38e/>
Note that the chips are NOT soldered.
[quote]I didn't find the case to come apart easily at all. I ended
up using the dental floss method of getting it apart. That's
from the hpmuseum.org forum.
[/quote]
Good idea. However, I've gotten fairly good with the brute force
method. I just pull the two plastic case parts apart until the
locking hinge abomination snaps open. I've never cracked one.
However, it does take some brute force and nerves of steel.
[quote]The keyboard on mine has a
metal dome for each key, and all the domes are held in the
right place by a sheet of plastic tape. So I cut through
the tape around the misfiring dome and removed it, cleaned
it, and put it back. It seems to work fine now.
[/quote]
There's also no plastic tape domes over the keys. Instead, it's
flexible PCB with domes molded into the plastic, with traces running
all over the plastic. There's no sticky tape. The plastic is part of
the sandwitch held in place by the edge clips. Cutting the plastic in
the manner of your example would end up cutting a trace. Fortunately,
removing the plastic dome sheet on my HP38e exposes the key contacts,
which can then be cleaned.
Your HP38c and my HP38e are quite different.
[quote]I took pictures of the keyboard and the bottom latch:
http://drop.io/HP38C_KeyRepair
[/quote]
Nice. Thanks.
Now to get it back together...
--
Jeff Liebermann jeffl at (no spam) cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558 |
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| Peabody... |
| Posted: Wed Oct 28, 2009 9:40 pm |
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Guest
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Jeff Liebermann says...
[quote]Your HP38c and my HP38e are quite different.
[/quote]
Yes, a completely different design. The early 38Cs were like yours
too.
[quote]Now to get it back together...
[/quote]
:-)
Well, it may be 25 years old, but I still love this
calculator. And I didn't see any on Ebay. That's a bad
sign I think. |
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| Jeff Liebermann... |
| Posted: Thu Oct 29, 2009 9:42 am |
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On Wed, 28 Oct 2009 22:40:30 -0500, Peabody
<waybackNO784SPAM44 at (no spam) yahoo.com> wrote:
[quote]Jeff Liebermann says...
Your HP38c and my HP38e are quite different.
Yes, a completely different design. The early 38Cs were like yours
too.
[/quote]
I've been collecting and repairing HP calcs on the side for about 30
years and I've never seen one built like the one in your photos.
Perhaps I'm leading a charmed life or haven't seen enough calculators.
(Most common repair is rebuilding battery packs and cleaning out the
damage caused by leaking cells).
[quote]Now to get it back together...
:-)
[/quote]
It's back to gether and working with no broken plastic. Never mind
that I initially installed the LED assembly backwards, missed on the
slide switches, and had a difficult time with the battery board. It's
been a while since I've worked on these, and you're right, the design
sucks.
[quote]Well, it may be 25 years old, but I still love this
calculator. And I didn't see any on Ebay. That's a bad
sign I think.
[/quote]
More like 30 years. Search again for hp35c and hp35e. There's one of
each for sale.
--
Jeff Liebermann jeffl at (no spam) cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558 |
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| Jeff Liebermann... |
| Posted: Sun Nov 01, 2009 6:00 am |
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Guest
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On Sun, 01 Nov 2009 21:13:08 +1000, Bob Larter <bobbylarter at (no spam) gmail.com>
wrote:
[quote]Jeff Liebermann wrote:
Sigh. Time to tear one apart. I couldn't find an HP38c in my pile,
but did find three HP38e calculators. I tore one apart and tooks some
photos:
http://www.11junk.com/pics/hp38e/
Note that the chips are NOT soldered.
Holy shit!
[/quote]
Good guess. I just finished rebuilding my septic tank. Not fun and
very expensive.
[quote]Until I looked at your photo, I thought that you meant that
the legs had corroded, or that the chips were socketed, or something
like that. I'm amazed that they were that cheap when they were
manufacturing them, or that they've lasted so long!
[/quote]
I moved the photos to:
<http://www.11junk.com/jeffl/pics/hp38e/>
Sorry(tm) about the grainy photos. I was in a rush and didn't bother
getting better lighting or using the flash.
No soldering or sockets. Even the LED array is solderless. It's
really a minimalist design.
The main PCB is actually a flexible circuit board, which relys on
pressure from the clips along the edge, cellular foam backing, and
stiffness in the plastic frame, to maintain electrical contact. It's
generally a workable system, but requires considerable manufacturing
precision. I've seen intermittents, but only when I do a sloppy job
of re-assembling the sandwidth.
One nice feature is that it makes replacing active components quite
easy. Unfortunately, tearing the HP-3x series cases apart is neither
easy or fun. I don't think it was designed to be easily repaired.
There are also some nasty symptoms caused by this method of
contruction. Here's a long thread on missing digits and segments on
the display. Besides bad connections, I've found it can be caused by
blown chips, probably by someone inserting them backwards (easy to do)
or in the wrong position (also easy to do) and applying power:
<http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv013.cgi?read=37024>
--
Jeff Liebermann jeffl at (no spam) cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558 |
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| Bob Larter... |
| Posted: Sun Nov 01, 2009 6:13 am |
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Guest
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Jeff Liebermann wrote:
[quote]Sigh. Time to tear one apart. I couldn't find an HP38c in my pile,
but did find three HP38e calculators. I tore one apart and tooks some
photos:
http://www.11junk.com/pics/hp38e/
Note that the chips are NOT soldered.
[/quote]
Holy shit! Until I looked at your photo, I thought that you meant that
the legs had corroded, or that the chips were socketed, or something
like that. I'm amazed that they were that cheap when they were
manufacturing them, or that they've lasted so long!
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
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