Casio FX 451 calculator from 30 years ago

It just so happens I have one of these on my desk!

Look carefully and you will see that the hard plastic top surface of the calculator - where the buttons, display, solar cell etc, are - overhangs the soft vinyl just a little. Put your fingernail or a guitar pick in between the vinyl and the hard plastic and slide it back and forth.

On the left - the long side that is not next to the hinge - there is one plastic locking tab in the middle - just north of the "SHIFT hyp" button.

On the bottom, there are two tabs - one between the 0 and . keys, and another between the = and M+ keys.

The top has two tabs, in the same places as the bottom.

The right has one tab, in the same place as the left side.

The guts/works of the calculator are attached to the keys, and will come up once you've released the locking tabs. The back cover - what the guts snap into - is white plastic and (mostly) five sides of a box - it seems to stay in the wallet.

The flex cable to the membrane keys in the right side is about 30 mm wide and attaches to the guts just behind the divide, subtract, and M+ keys. The joint is covered by a removable plastic piece - I didn't take that off, so I don't know if it's soldered, or has a connector, or what.

I took a few photos, available at

. One of them shows the left side locking tab, one shows the bottom locking tabs, and one is a view of the back of the guts. You can just about see the flex cable on this last one.

Back in the day (late 80s, early 90s), these Casios were just the thing, if you couldn't afford an HP. I had the FX-115 in high school and got the FX-451 later on.

Matt Roberds

I had tried a probe in that area, will have to try some low-heat hot-air , as it did not want to cleave apart

I have dodgy fingernails and no guitar pick, so I use a Bic ball-point pen cap instead for that sort of job. Could also try toothpick or cocktail stick...

Mike.

I'm amazed the plastic has not failed at the hinge, with about daily opening and closing for 30 years, its not gone rigid or split

There are a couple of them on Ebay for US $50 or less. Might be the way to go, compared to labor (labour) costs.

--Tim

thanks for that, I'd misinterpreted how it was assembled. More like standard TV zapper but with the wallet sandwiched between the 2 parts of the hard plastic casing