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wmundstock · (This post was last modified: 11-11-2023 10:34 PM by wmundstock.)

(05-07-2020 04:58 PM)hb9fsx Wrote: Hi guys
I am working on an interesting thing. I got from an old friend a HP 15c. It is working, BUT it has been abused badly:

* dropped on the floor several times. A little piece from the rear half of the plastic case is broken off. Besides that, almost ALL of the internal heat stakes are broken, and one of the pieces was now between the LCD module and the front window.
* it was used in a smoker household: the entire keypad and front panel is full of ... don't know how I should call it, sticky goo. Even the keys were almost unreadable.
* doesn't pass the keyboard self test: because the keyboard is held by those internal heat stakes, the keys don't make good contact all the time. So sometimes it is not possible to push them all.

Since I actually want to use this calculator, I have decided to open it and tried to clean it. It works! looks almost like brand new! and after I cleaned the LCD module, it looks nice and sharp and crisp. It even passes the self test ;-)

Now two questions:

1. I have found two very tiny springs on my desk. They MUST be from this calculator, because I don't know from what else they should be ;-) so where do they belong?
2. How to reassemble it: I have put in the keys and this little rubber mat which is under the keys. All good so far and I can also but the PCB back in. Since the heat stakes are broken off, it will not be possible to melt all of them with my soldering iron. On the other hand it is necessary to have a very good pressure from the PCB to the front panel. So I thought about a different method: if I would put a piece of foam rubber or neoprene between the PCB and the calculator back case, that would give some pressure and press the PCB nice and tightly to the front panel. Any better ideas? I am not a particular friend of gluing. And I also don't really like those heat stakes.

I am planning a similar project. The 15C I got has the board saying MADE IN USA, which is good and the calculator itself says Brazil on the back.

The keys and self test are good. Enter key is working but lost its "click" feel a little bit.

My main complaint is the display. I can't tell if its dirt or what, but it is a bit opaque. It seems like the problem is the interior of the window. Maybe its made of a sandwitch with 2 films and one is peeling of. That kind of feel. Attached some pictures from the microscope.

Questions are:
1. I suppose to remove you have to cut the little black "smashed plastic dots". How do you recommend doing that?
2. How do you assemble it back? Do you put it back in place and melt plastic? Any thoughts on the process?
3. Can I replace that window with maybe the window of another calculator? Those with big display or something like that? What material is used there?

Thanks!
Walter