How to fix cracked display plastic cover?

[Maximilian Hohmann]

Hello,

I recently acquired a Casio FX-602P for very little money - usually these calculators go for three-figure-amounts of Euros/Dollars. This is a quite powerful calculator from 1981, a kind of competitor to the HP-41C or the Ti-59. It has constant memory, an alphanumeric display and can be expanded with a printer and cassette recorder interface for permanent storage.

Unfortunately the seller, probably disappointed by the auction result, did not pack the calculator very well (he did not pack it at all but just put it in a plain paper envelope) and it arrived with a cracked display, the pictures are below.

So now I wonder what I can possibly do about it without too much hassle. A drop of superglue maybe that creeps into the crack and makes it less visible? Or any other glue that will have the same effect? A drop of silicon oil perhaps? Or something else?

Regards
Max

[Jeff_Birt]

You would need a glue that has the same refractive index as the plastic. This is also the trick when repairing windshield cracks. Then you would need to be able to pull the glue all the way through the crack under vacuum.

In my experience superglue will leave a white haze and acetone will look a tiny bit better bit the crack will still be visible and you will probably make it less transparent. (Been there done that.)

[battlecoder]

(11-20-2024 07:42 PM)Jeff_Birt Wrote:  In my experience superglue will leave a white haze and acetone will look a tiny bit better bit the crack will still be visible and you will probably make it less transparent. (Been there done that.)

This has been my experience too.

[Martin Hepperle]

Can you take the calculator apart?
I would avoid any glueing with the display pane in place.
As has been said superglue is less suitable due to "fogging".

If the pane is of polystyrol, a clear liquid model aircraft cement (e.g. Revell Contacta) could be used. It locally dissolves the polystyrol (and ABS) and is transparent. After drying (several days) you could wet-sand (grit 600-1200)and polish the surface. The crack will still be visible, but better than the current condition.

Alternative 1: buy some Plexiglass sheet and machine a completely new display cover. This would be the best solution.

Alternative 2: make a silicone rubber mold and use clear casting resin to create a new pane. Also requires sanding and polishing.

Alternative 3: find another similar donor calculator.

Martin

[Maximilian Hohmann]

Hello!

(11-21-2024 07:56 AM)Martin Hepperle Wrote:  Can you take the calculator apart?

I could (had a quick look under the cover) but I am afraid to damage the flex-cable that connects the LCD to the main board in the process. Better a crack than missing rows of pixels! So I will try to do something from the outside first.

If the cover is made from polystyrene (or "Polystyrol" as it was named by it's inventor) a drop of acetone might creep into the crack and seal it maybe? After all plastic glue is mostly made from solvent(s).
Making a new cover is probably not worth the effort because the calculator's overall cosmetic shape is maybe 3 to 4 out of 10.

Regards
Max

NB: Looking at the manual for this calculator, which can still be downloaded from the Casio support site 41 years after it's introduction, I could see once again how well HP manuals were written! The Casio manual is a big mess compared to anything HP has ever published!

[RPNerd]

(11-21-2024 12:07 PM)Maximilian Hohmann Wrote:  NB: Looking at the manual for this calculator, which can still be downloaded from the Casio support site 41 years after it's introduction, I could see once again how well HP manuals were written! The Casio manual is a big mess compared to anything HP has ever published!

Compared to anything HP produced in the golden era of the '80s, I'd agree. But compared to anything produced more recently, it's a much closer call. Only yesterday I was looking at something in one of the official manuals for the HP 50g and it was stuffed full of grammatical errors. Something like 2 or 3 in the few lines that I was reading alone.