HP 38C calculator disassembly?

[Peabody]

Has anyone here ever taken apart one of these calculators? My "6"
key is not registering all the time, and I thought I might be able
to clean out the crud in there and make it work again. But it's not
obvious how one would take one of these apart. I've Googled, but
haven't found anything. If anyone has a relevant link, I would
appreciate it.

FWIW, I still think these HPs are wonderful. RPN forever! We don't
need no stinkin "=" key.

 

[William Sommerwerck]

Does the calculator have rubber feet on the back? There are often screws
under the feet.

I had one of the original HP-35s (1972). I'd never heard of RPN, and thought
"What's going on here?" After a few minutes using the calculator, I was
permanently converted. Why would anyone use algebraic entry?

 

[propman]

Peabody wrote:

Has anyone here ever taken apart one of these calculators? My "6"
key is not registering all the time, and I thought I might be able
to clean out the crud in there and make it work again. But it's not
obvious how one would take one of these apart. I've Googled, but
haven't found anything. If anyone has a relevant link, I would
appreciate it.

FWIW, I still think these HPs are wonderful. RPN forever! We don't
need no stinkin "=" key.

don't see anything specific re: 38c at the following site but it might
give you an idea on how to proceed:


http://www.hpmuseum.org/disasm.htm

 

[AZ Nomad]

On Tue, 27 Oct 2009 11:48:35 -0700, propman <propman@nowhere.ca> wrote:

Peabody wrote:
Has anyone here ever taken apart one of these calculators? My "6"
key is not registering all the time, and I thought I might be able
to clean out the crud in there and make it work again. But it's not
obvious how one would take one of these apart. I've Googled, but
haven't found anything. If anyone has a relevant link, I would
appreciate it.

FWIW, I still think these HPs are wonderful. RPN forever! We don't
need no stinkin "=" key.



don't see anything specific re: 38c at the following site but it might
give you an idea on how to proceed:

http://www.hpmuseum.org/disasm.htm

HP's are not easy to disassemble. Even with well written directions,
you're still likely to damage or destroy your calculator. I'd suggest
using some contact cleaner to get the crud out. If the membrane
switch is worn out then you're only option is to replace the keyboard
and replacing the entire calculator with a used one is likely to be
cheaper.

 

[Charles]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:hc7cq2$hvf$1@news.eternal-september.org...

Does the calculator have rubber feet on the back? There are often screws
under the feet.

I had one of the original HP-35s (1972). I'd never heard of RPN, and
thought
"What's going on here?" After a few minutes using the calculator, I was
permanently converted. Why would anyone use algebraic entry?

Reverse Polish Notation ... was judged as a racial slur when HP first hit
the market ;&gt

Seriously, I was amazed at how easy it was to learn and how many keystrokes
it saved with chain calculations. I am retired and have lost track of RPN
.... is it available in modern calculators?

 

[William Sommerwerck]

I am retired and have lost track of RPN
... is it available in modern calculators?

HP still sells calculators with RPN. These sometimes include algebraic
notation to simplify the entry of formulas when programming.

It should be noted that almost all "algebraic" calculators are hybrid,
mixing RPN with algebraic entry.

 

[Dave Platt]

In article <hc7th8$lkp$1@news.eternal-september.org>,
Charles <charlesschuler@comcast.net> wrote:

Seriously, I was amazed at how easy it was to learn and how many keystrokes
it saved with chain calculations. I am retired and have lost track of RPN
... is it available in modern calculators?

A fair number of current HP calculator are bi- or tri-lingual - they
support RPN as well as algebraic. The HP12C is RPN-only.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Jeff Liebermann]

On Tue, 27 Oct 2009 13:00:31 -0500, Peabody
<waybackNO784SPAM44@yahoo.com> wrote:

Has anyone here ever taken apart one of these calculators?

Yes.

My "6"
key is not registering all the time, and I thought I might be able
to clean out the crud in there and make it work again.

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.

My batting average is about 50%. I've worked over about 4 of the
series (HP31,32,33,37,38...). I fixed keyboards on two but also
destroyed two others. The ones I destroyed were partially working
when I started, and had more dead keys when I was done.

FWIW, I still think these HPs are wonderful. RPN forever!

Yep. I have a small collection and still use them on a daily basis.

We don't need no stinkin "=" key.

The HP35s has both Enter and "=" keys (although the "=" key is
somewhat hidden).

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[iws]

"Peabody" <waybackNO784SPAM44@yahoo.com> wrote in message
news:2zGFm.11593$86.877@newsfe15.iad...
|snip

| FWIW, I still think these HPs are wonderful. RPN forever! We don't
| need no stinkin "=" key.

Ah yes, RPN vs. algebraic. Kinda the Mac vs PC wars of the 1970's. Or the
Betamax vs. VHS wars of the 1980's.

 

[Jeff Liebermann]

On Tue, 27 Oct 2009 20:12:09 -0700, "iws" <nospam@nospam.com> wrote:

"Peabody" <waybackNO784SPAM44@yahoo.com> wrote in message
news:2zGFm.11593$86.877@newsfe15.iad...
|snip

| FWIW, I still think these HPs are wonderful. RPN forever! We don't
| need no stinkin "=" key.

Ah yes, RPN vs. algebraic. Kinda the Mac vs PC wars of the 1970's. Or the
Betamax vs. VHS wars of the 1980's.

Yep.

RPN is better, but there are many more algebraic calculators.
Mac is generally better, but PC's are more common and cheaper.
Beta has better image quality, but VHS didn't have a royalty attached
and is therefore more popular.

Success through mediocrity.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Reinhard Zwirner]

Jeff Liebermann schrieb:

[...]
The HP35s has both Enter and "=" keys (although the "=" key is
somewhat hidden). ^^ ^^

Hi Jeff

Where? I bought my HP35 in 1974 and haven't found this key till now!

Very interested

Reinhard

 

[William Sommerwerck]

The HP35s has both Enter and "=" keys (although the "=" key
is somewhat hidden).^

Where? I bought my HP35 in 1974 and haven't found this key till now!

He should have said HP-35S. See above.

 

[AZ Nomad]

On Wed, 28 Oct 2009 19:12:51 +0100, Reinhard Zwirner <reinhard_zwirner@web.de> wrote:

Jeff Liebermann schrieb:

[...]
The HP35s has both Enter and "=" keys (although the "=" key is
somewhat hidden). ^^ ^^

Hi Jeff

Where? I bought my HP35 in 1974 and haven't found this key till now!

HP35s != HP35

 

[Reinhard Zwirner]

AZ Nomad schrieb:

On Wed, 28 Oct 2009 19:12:51 +0100, Reinhard Zwirner <reinhard_zwirner@web.de> wrote:
Jeff Liebermann schrieb:

[...]
The HP35s has both Enter and "=" keys (although the "=" key is
somewhat hidden). ^^ ^^

Hi Jeff

Where? I bought my HP35 in 1974 and haven't found this key till now!

HP35s != HP35

Many thanks to you and William! I did misinterpret the s as a plural s.
Now I know that there is a HP 35 revival calculator ;-) ...

Best regards

Reinhard

 

[Jeff Liebermann]

On Wed, 28 Oct 2009 19:12:51 +0100, Reinhard Zwirner
<reinhard_zwirner@web.de> wrote:

Jeff Liebermann schrieb:

[...]
The HP35s has both Enter and "=" keys (although the "=" key is
somewhat hidden). ^^ ^^

Where? I bought my HP35 in 1974 and haven't found this key till now!
Very interested
Reinhard

The HP35 does NOT have an "=" key. The new and allegedly improved
HP35s does. See:
<http://www.hpcc.org/datafile/V26Special/the35s.pdf>
It's above the +/- key, to the right of the Enter key.

The HP35s was suppose to be an update of the classic HP35 calculator.
Unfortunately, just about everything is different. It's also full of
bugs and annoyances:
<http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=735>
<http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv017.cgi?read=126708>
I use mine effectively, but I'm still disappointed (and disgusted).


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Peabody]

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.

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

 

[Jeff Liebermann]

On Wed, 28 Oct 2009 20:03:46 -0500, Peabody
<waybackNO784SPAM44@yahoo.com> wrote:

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.

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.

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.

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.

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.

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.

I took pictures of the keyboard and the bottom latch:
http://drop.io/HP38C_KeyRepair

Nice. Thanks.

Now to get it back together...




--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Peabody]

Jeff Liebermann says...

Your HP38c and my HP38e are quite different.

Yes, a completely different design. The early 38Cs were like yours
too.

Now to get it back together...

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.

 

[Jeff Liebermann]

On Wed, 28 Oct 2009 22:40:30 -0500, Peabody
<waybackNO784SPAM44@yahoo.com> wrote:

Jeff Liebermann says...

Your HP38c and my HP38e are quite different.

Yes, a completely different design. The early 38Cs were like yours
too.

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).

Now to get it back together...

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.

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.

More like 30 years. Search again for hp35c and hp35e. There's one of
each for sale.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sun, 01 Nov 2009 21:13:08 +1000, Bob Larter <bobbylarter@gmail.com>
wrote:

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!

Good guess. I just finished rebuilding my septic tank. Not fun and
very expensive.

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!

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@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558