The Museum of HP Calculators

HP Forum Archive 16

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HP-41 Keyboard: Cracked Dome?
Message #1 Posted by Tom Salmon on 27 Jan 2007, 5:16 p.m.

I purchased a used HP41-CV on eBay for my daughter for daily use since I won't let her take my CX to school. The 4 key works, but does not click. I have carefully looked at it from the outside, and it appears to have the same rest height and travel as the other keys. If the dome is cracked, will the key sag, or will the rest height be lower? I can return this calculator, so I haven't opened it up yet. I have read every post from 1999 and then some, about these keyboards, and I am willing to venture in as long as it is not a cracked dome. The expansion ports, battery area are corrosion free, and the rest of the keys feel very good. I would prefer to keep this if anyone thinks the standard cleaning mentioned in several years of past forum posts has a good chance of restoring the tactile feel.

      
Re: An Updated Version of the 15c Would Make Money...?
Message #2 Posted by db (Martinez, California) on 27 Jan 2007, 9:28 p.m.,
in response to message #1 by Tom Salmon

You have nothing to loose. Trying to return ebay purchases is a real drag most of the time. Unless it's someone like Mike, odds are they are selling junque they found at the flea that even I passed up. They don't want it back.

Remember: a couple of hours soaking and cleaning in +/- 70% alcohol is a good method but make sure you get everything off the screen when you are done or it will etch the clear plastic. I have had good luck with MG Chemicals "Super Contact Cleaner" on the keys. I think that most tv tuner cleaners will be fairly safe to use on the 41's materials because since they are a one-size-fits-all product; they shouldn't have anything that dissolves common plastics. Your mileage may vary.

I have cleaned a dead key from the back, using the (Randy's? David's?) tiny wire-brush-through-the-hole method. It had acted like your's and it is almost as good as new now. A lot of goop can kill the clickness.

A lot of dads get their kid a 33s. YOU are a class act my man.

BTW: Here is a link to see how a great engineer uses the Universal Solvent http://echosphere.net/star_trek_insp/insp_alcohol.png.

Edited: 27 Jan 2007, 11:27 p.m.

            
Re: An Updated Version of the 15c Would Make Money...?
Message #3 Posted by Tom Salmon on 28 Jan 2007, 9:51 a.m.,
in response to message #2 by db (Martinez, California)

Thanks for your reply and insight.

Besides a preference for RPN, I really like the tactile click/positive feedback of the keys.

If I could buy a 15C, I would. I'm not having the best of luck on eBay. I bought a 28C and had to return that due to a totally dead "+" key. After reading 6 years of forum posts about keyboards, maybe I could have fixed it. Now I have the CV that has the cruddy 4 key. The thing that seems strange is that all of the other keys feel perfect, so I'm wondering why this one key could be dirty. It seems like many of the keys would not feel so "new".

I am considering buying the new RPN graphing calculator that is about $100, but no one has one I can actually touch. Everybody has it online with no direct pick-up. I have a feeling I won't like the new keys as much as the 41 keys.

Any advice on adhesive to glue back on the rubber feet so they won't fall off, but can be removed again if necessary?

Tom

                  
Re: An Updated Version of the 15c Would Make Money...?
Message #4 Posted by bernie on 28 Jan 2007, 3:26 p.m.,
in response to message #3 by Tom Salmon

Tom,

keys which work but lack the HP "clic" often have broken contact strips. Typically, one side of the individual punched-out contact strip is broken, while the other side still is intact. On the classics it can be repaired, but with the HP41 I'd recommend against opening the keyboard, as it may turn matters worse.

regards, Bernie

                        
Re: keyboard problems
Message #5 Posted by Randy on 28 Jan 2007, 4:47 p.m.,
in response to message #4 by bernie

Classic LED machines and 41 keyboards are very different. Classics have strips of that fracture at the edges as Bernie mentions. 41's do not share the same design. Recognizing the inherit stress point in the strip design, HP changed things with the 41 using individual stamped domes.

On a 41, while it can happen, a cracked dome is really quite rare. My money would be on crud inside the key dome. Cleaning is where I would start.

Quote:
I bought a 28C and had to return that due to a totally dead "+" key. After reading 6 years of forum posts about keyboards, maybe I could have fixed it.
I doubt it... once opened, you cannot reclose a clamshell model.

Quote:
Any advice on adhesive to glue back on the rubber feet so they won't fall off, but can be removed again if necessary?

Don't use glues, double sided carpet tape is the way to go.

Edited: 28 Jan 2007, 4:50 p.m.

                              
Re: keyboard problems
Message #6 Posted by Tom Salmon on 30 Jan 2007, 9:34 p.m.,
in response to message #5 by Randy

Guys, thanks for all the advice. I have confirmed that the dome is not cracked. I used a little alcohol and a small bristle to clean via the access hole. The 4 key regained it s click, but I think I just thinned out the goop, because it quit clicking again after a couple of hours. I think I need to use an ultrasonic cleaner if I understand posts from the forum archives.

            
Re: An Updated Version of the 15c Would Make Money...?
Message #7 Posted by Walter B on 28 Jan 2007, 12:18 p.m.,
in response to message #2 by db (Martinez, California)

Hi db,

how about changing your default subject? d;-)

Best regards!

                  
how?
Message #8 Posted by db (Martinez, California) on 29 Jan 2007, 12:06 a.m.,
in response to message #7 by Walter B

Walter; I'm game. How do you do that? And while you're at it; please explain to me why a late model IBM brand ThinkPad with XP Pro either can't communicate with this forum correctly or it posts and then the postings evaporate overnight. My old Trashiba didn't do this, and it was so bad that Toshiba gave me over $700 in refunds on a $1000 laptop.

And people ask me why i still use an hp 41.....

                        
Re: how?
Message #9 Posted by Marcus von Cube, Germany on 29 Jan 2007, 3:54 a.m.,
in response to message #8 by db (Martinez, California)

I assume you are using IE as your default browser. You might be luckier with FireFox or Opera.

Edited: 29 Jan 2007, 3:54 a.m.

                              
Re: how?
Message #10 Posted by db (Martinez, California) on 30 Jan 2007, 1:21 a.m.,
in response to message #9 by Marcus von Cube, Germany

MvC; I use Mozilla Firefox - started because no one was targeting it with viruses. Not so sure about that now, but i'm used to it. Never tried Opera. Not a fan of the music. thanks for the note & ideas. - d

                                    
Not saving subject as a default with Firefox (was: how?)
Message #11 Posted by James M. Prange (Michigan) on 30 Jan 2007, 7:55 p.m.,
in response to message #10 by db (Martinez, California)

Firefox, for whatever reason, seems to consider the MoHPC subject line to be a password, or maybe a user name.

Anyway, click on Tools -> Options... -> Security, and under "Passwords", if you have the "Remember passwords for sites" box checked, then click on "Exceptions..." and add "http://www.hpmuseum.org" to the list.

Regards,
James

Edited: 30 Jan 2007, 7:56 p.m.

                                          
Re: Not saving subject as a default with Firefox (was: how?)
Message #12 Posted by Marcus von Cube, Germany on 31 Jan 2007, 2:52 a.m.,
in response to message #11 by James M. Prange (Michigan)

That's a good explanation. Since I'm a registered user, I don't see the "password" field in the response window. So I don't have the trouble. FF seems to recognize an entry field near a password field as a candidate for a username that is worth remembering.

            
Re: An Updated Version of the 15c Would Make Money...?
Message #13 Posted by David Smith on 29 Jan 2007, 10:50 a.m.,
in response to message #2 by db (Martinez, California)

No, NEVER soak the machine in alcohol. The key domes are held down with an adhesive sheet. Alcohol can cause the sheet to lift. In extreme cases I have used ultrasonic cleaners with water.

When cleaning contacts and boards with alchohol, keep it off the display window. It leaves a white stain behind (that can be removed, but you have to remove the display module on 41's (halfnuts are pretty much domed, removing the display means cutting the keyboard loose which pretty much wrecks the machines).

      
Re: HP-41 Keyboard: Cracked Dome?
Message #14 Posted by Karl Schneider on 28 Jan 2007, 3:24 p.m.,
in response to message #1 by Tom Salmon

Hello, Tom --

Quote:
I purchased a used HP41-CV on eBay for my daughter for daily use since I won't let her take my CX to school. The 4 key works, but does not click. I have carefully looked at it from the outside, and it appears to have the same rest height and travel as the other keys. If the dome is cracked, will the key sag, or will the rest height be lower?

Since the key rests at normal height, I'd suspect gunk underneath the key. I bought a heavily-used HP-41C whose R/S key had little tactile feedback. An ultrasonic cleaning by Randy at www.fixthatcalc.com improved matters significantly.

-- KS

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