HP41 Upper Screw Well Busted



#8

Hi All,

I purchased an HP41CV off of ebay and while it works, it has some problems with the screw posts and use of the plug in modules. I'm trying to work through those and have read the articles on how to repair the posts.


What I'm not able to find is what the upper screw wells in the back cover are supposed to look like. Here's a picture of what mine looks like.

Picture of Broken Screw recess


Does anyone have an image of a correct one? Are there any repair procedures for this problem? Any suggestions?

Thanks,
Colin




Edited: 16 July 2012, 2:07 p.m. after one or more responses were posted


#9

Hi.

I have successfully repaired some upper case with broken basis, like the one in the picture. I have no pictures so far, will provide some this very week when I´ll have to repair at least five units with this problem.

My procedure is like this (in brief): I cut a small piece of square plastic that is thick enough holding the screw and with dimensions allowing it to fit in the space for it. Please, check the picture below (yep, I took yours and draw over it, sorry...)

The red lines are taken from the small plastic tabs that align the IO/battery contacts assembly. These lines tell you the size of the small plastic cut, drawn in blue lines (sorry for the kid-like drawing...). You must also check for the lateral size by testing with the IO/battery assy as it actually 'shows' how the plastic cut must look like. Then, after fitting it in place, you can use any of the existing glues for keeping the plastic cut in place. There are some excellent ones that actually dissolve the plastic, like welding it (I never remember the chemical composition...). Drilling the hole is an easy task, then.

Hope it helps a bit as a suggestion.

Success!

Luiz (Brazil)

Edited: 16 July 2012, 11:26 a.m.


#10

Luiz,

Thanks for the response. What you say makes sense. I guess I have to file down the remainder of the old screw wells to be flush with the surface of the case. Any suggestion on how to ensure exact alignment of the plastic piece for gluing? seems that if I make a mistake I'm screwed. Maybe I can install the IO assembly while the glue is still wet? But I'll have to be very careful that no glue is seeping out the edges. Maybe try to install and remove before the glue dries?

Also, if anyone has the (USA) brand name of the plastic dissolving glue you mention, or other suggestions for glue, I'd appreciate it. I'm familiar with model glue, super glue and with epoxy. The former two might not hold up to the drilling. The latter might be too thick.


#11

Hi, Colin.

Quote:
I guess I have to file down the remainder of the old screw wells to be flush with the surface of the case.
Yes, leveling the surface will lead to wilder contact surface.
Quote:
Any suggestion on how to ensure exact alignment of the plastic piece for gluing? seems that if I make a mistake I'm screwed.
I'd suggest you to carefully inspect the IO/battery contact assembly block. You'll see where does the plastic cut might fit. I slightly rounded the corners of the ones I used as an aid for final alignment. The part of the IO/battery block that touches the case will surely guide you. And you will also see that the plastic tabs are the best references so to know the upper and lower limits of the plastic cut.
Quote:
Maybe I can install the IO assembly while the glue is still wet? But I'll have to be very careful that no glue is seeping out the edges.
I remember using a non-permanent, easily removable glue - like white, paper glue - to test the alignment so I could precisely mark where to permanently glue it later.

I am confident that based on your questions you will surely find a way to do it. And believe me, our way is usually the way we'll never forget. Try some non-permanent experiments, like the white, paper glue, and you'll find your own, safe way to go ahead. I like to experiment myself, as you can see here, so I support experimenting as well. I am also a teacher...

I am totally sorry for not to remember which chemical compound is required in the plastic welding. I never found it here, I tried the one used in acrylic molding and it has given me some good results. I'll check which component is the main one in this case, but I know it does not work in some types of plastic, must test first.

Success!

Luiz (Brazil)

Edited: 16 July 2012, 5:31 p.m.


#12

Guys, the method Luiz describes is pretty much what I do too, and at one stage in the past, I dicussed this with Geoff Quickfall, and his method also similar. The new plastic piece is what I call a "tablet".

Just a few tips from my experience ..1) try to find similar plastic to the original to make the replacement "tablet". 2) Use the "disolving" glue, which I beleive is generically known as model airplane glue, the brand name here in Australia is "Tarzan's grip", and I think the chemistry is known as polystyrene glue, the key to that being that the stuff disolves polystyrene very well !! - so that might be a good test. 3) Finally, I use the battery connector block to gauge the shape and size "tablet", and also to locate the tablet while the glue sets. I actually use some "blu tac" to hold the tablet in the connector block to place it, and then let the glue set.

I hope that helps.

Cheers,
John

#13

"Ambroid Proweld" or "Ambroid Pro Weld"
It is water clear, has very low viscosity and low surface tension (so it flows extremely well). It actually melts what you're gluing, makes it flow, and then evaporates as the joint cures. What is left is e.g. styrene/styrene (your original materials), not styrene/"glue"/styrene. I can attest to its working well with styrene. This stuff sets up in seconds, not minutes; there is no "working time".

My nose says the active ingredient is acetone.

#14

Hi Colin,


>Are there any repair procedures for this problem?

In two words: Fiber Washers (according to this link).


Seems to have some validity, as it appears it would provide some *give*.


Matt

Edited: 17 July 2012, 12:39 a.m.


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