Hello all,
I am trying to fix a halfnut 41CX. Among other things, the number 3 key does not work. I realize there may not be a lot I can do about that, but I thought I'd ask, is there anything quick I can try?
The complete dissasembly procedure looks quite involved, so I'd like to try anything else first.
Thanks,
Ion Abraham
Albuquerque, New Mexico
You can try compressed air on the outside of the keyboard to see if something dislodges. If that doesn't work, you may need to remove the back of the unit and blow compressed air directly on the backside of the keyboard and around the sides.
thats a good first try but if that dosn't work try blue shower II (tspray@techspray.com)
Hello all,
Well, I tried compressed air and contact cleaner, and that didn't do it. So I would actually like to get at the key.
My question is, how do you lift the main circuit board in order to get at the keys? I think the instructions on this site from Steve Loboyko refer to a Fullnut. My CX Halfnut has one continuous board from the screen to the lowest key. There are four metal tabs at the top and four other tabs that stick through the board. They are bent so as to hold down the board (I think). I straightened those, but still the board does not lift off. Are there other tabs? I am trying to be careful and not force things.
Any advice would be greatly appreciated.
Regards,
Ion Abraham
Albuquerque, New Mexico
I took apart an HP41-CX Halfnut with very bad sticky keys. I found that the board that has the key contact circuit is attached to the top case part by plastic stubs or pins (total of 36) that are molded into the plastic top case. The key contact printed circuit board (PCB) is placed over the keys onto the plastic stubs, then the plastic stubs are melted down to attach the PCB. The four metal tabs at the top only hold the display LCD onto the key contact PCB. I carefully cut the plastic stubs off to remove the key contact PCB. I was able to clean the contacts, but now the plastic stubs are not long enough to reattach the key contact PCB. I found some very small screws but I am not sure they will work.
The moral to this long story is that I would not try to get to the key contacts directly or you will have an HP41 like mine that is a box of parts. Keep trying the compressed air or some recommended contact cleaner.
If you use contact cleaner, you will need to spray a small amount into the feedthrough holes on the back of the key contact PCB. The center of each key contact has a plated feedthrough hole in the PCB. Then press the key to make some cleaning action. Hope this helps.
Using the compressed air or contact cleaner from the top next to the keys will not help. Between the keys and the key contact PCB is a rubber insulator about 1/16-1/8 inch thick. Also, each key contact has a metal dome over contact area which is attached to the PCB with a large piece of tape.
If anyone else has experience in removing the key contact PCB and reattaching with success please comment.
I also have a keyboard problem. My "enter" key has fallen on one end. It still works but I would like to fix the problem. It seems the spring has gone out. The only way I see to fix it is to remove the key contact board. But as Jerry has pointed out, the plastic post would not be long enough to replace the key contact board. Any ideals would be welcome.
what about this solution to reassembling the keyboard (i have not tried it yet, but i sure will be trying it on my next 41 rescue project):
1)reassemble the keyboard with the calculators top securely fixed on the workbench.
2) make a mounting fixture that applies gentle and evenly distributed pressure onto the keyboard, so that the ends of the mounting stubs are all flush with the surface of the keyboard pcb. all plastic stubs must still be reachable after installing the fixture. clean the stubs with alcohol.
3) this sounds weird, but works fine: burn some styrene sprue of your recently finished model kit and collect the fumes by holding some sheet metal approx. 5 sec. directly over the flame. don't do this in your *own* living room. be very careful...(cough, cough)
3) prepare some 2 component bond. do *not* use the epoxy or cyanacrylate type. try to find a bond (glue) on a methylmethacrylate basis; maybe your dentist can help you in this case. the german brand for this type of glue is 'Stabilit express'. scrape the fume residues from the sheet metal into the freshly mixed glue and stir well. this will give a nearly black appearence of the glue, without affecting the bonding quality.
4) give a drop of the bond on each of the plastic stubs and let the whole thing cure for 2 hours.
5) remove the mounting fixture.
hope, this will be usefull for someone!
just to clarify the procedure a bit:
when assembling, take the top half of the 41 and secure it onto the workbench *facing downwards*. then re- insert the keyboard- pcb. now, apply slight pressure on the keyboard-*pcb* (and not on the keyboard itself,as described earlier) so that the plastic posts are all at least flush with the pcb.
cheers, hans
I have used the clear "five minute" epoxy to repair keyboards on other brands of calculators after cutting off the melted plastic posts originally used to hold the keyboard together. These calculators are part of my collection and used only infrequently. I have also used epoxy to partially reattach the keyboard of a badly abused 12C. I gave this 12C to my brother, who has been using it daily without complaint.
I always use lots of rubber bands to hold the keyboard together while the epoxy cures.
Disclaimer: These are results are based on my own personal experience, your results may vary. :-)
I have done several keyboards by shaving off the heat stakes with an Exacto knife with the flat square blade. The adhesive that I use is call IC2000 Tire Cement by Bob Smith Adhesives. It is a cyanoacrylate (superglue) that is black in color. It has some kind of rubbery additive that makes it much less brittle than regular CA glues and is fairly thick and quite strong. It is sold at hobby shops (almost always with a stick on label personalized with the hobby shop's name) for gluing tires onto radio control race cars. Works great when rebuilding battery packs also.
I have not done this with a 41 but have done it with the Woodstock series.
Carefully peel off the melted part of each post. The post still sticks ever so slightly above the board.
After the board is repaired, I use a broad tip soldering iron and very lightly touch to the end of the post. You have to hold the board tightly in place while touching each post. After completed, it looks almost like new.
This still allows one more removal before having to resort to glue, which is permanent.
Hello all,
I am very grateful for all the responses to this question. It looks like the dissasembly procedure is surprisingly non trivial. I would be willing to try it, but first, would someone who has successfully done this before be willing to take on the task (for a fee of course)? I don't really need a guarantee of success, perhaps 50/50 would be OK.
On another tack, are there parts of a Halfnut CX that are useful as spares, besides the obvious detachables (battery terminals, etc.), from such a unit? This thing is pretty messed up. It turns out the R/S key is also bad, it's not very springy even, and the USER key is intermittent. I am thinking it may not be worth fixing.
Any thoughts?
Best regards,
Ion Abraham
Albuquerque, New Mexico
Hey Mike,
Was that you that just sniped me on the APF M55 on ebay, or was that another mwsebastion?