How to open a Casio FX-4000P?

[johanw]

I got a 2nd hand Casio FX-4000P and the only reason it is not working is that AFAIK the batteries are empty. However, the 2 screws on the back have apparently been opened and fastened by someone with either the wrong tool and / or no feeling for it with much too large a force so the heads are damaged and I can't unscrew them normally.

The head is very shallow, with small Torx in an old Nokia phone suffering from the same issue I got them loose by soldering a screwdriver in the screws but I don't think that is going to work here.

Any advice? Is there a way to get those screws off without damaging the rest of the calculator? And where would I look (from Europe) for decent replacement screws?

[vaklaff]

(08-07-2021 08:51 PM)johanw Wrote:  The head is very shallow, with small Torx in an old Nokia phone suffering from the same issue I got them loose by soldering a screwdriver in the screws but I don't think that is going to work here.

Great idea, thanks for sharing!

(08-07-2021 08:51 PM)johanw Wrote:  Any advice? Is there a way to get those screws off without damaging the rest of the calculator? And where would I look (from Europe) for decent replacement screws?

Be warned: I'm no handyman, others may have much better methods. But anyway...

It happened to me a with a few calculators too. What worked for me is scratching the head on two opposite edges to get enough hold for a flat-blade screwdriver. Of course, the head must provide enough space for the new "groves" but I've been lucky so far.

As for the technique, nothing complicated. Most of screws in calculators are very soft so just take a thin hard tool, be patient and scratch the screw's head until it's done :-) Once I borrowed a thin drill from a goldsmith and drilled instead of scratching, it was much faster but probably riskier too, I felt pretty nervous while doing it.

Even though I'm very clumsy and the results weren't pretty, in the end I was able to unscrew the screws. If the new hold was good enough I even let the "upgraded" screws keep their job :-)

Good luck and let us know!

[johanw]

(08-08-2021 10:17 AM)vaklaff Wrote:  Great idea, thanks for sharing!

I have to admit I had difficulties getting it to stick, but I managed by dipping the screwdriver in S39 and wetting the inside of the screw with it too. Of course I was careful not to get that stuff onto the pcb.

Quote:As for the technique, nothing complicated. Most of screws in calculators are very soft

I tried it with a small, sharp philips screwdriver and pressed quite hard, that gave enough grip to get them loose. 2 new CD2032 batteries and the machine switched on immediately.

I didn't even have to tune up the contrast (is that even possible on a 4000? I didn't see any keys for that) as was the case with my FX-8000G, when I replaced the batteries in that one my heart sank when I didn't see anything when I switched it on, until I got the idea to push up the contrast. That worked.

[Dave Britten]

(08-08-2021 12:30 PM)johanw Wrote:  I didn't even have to tune up the contrast (is that even possible on a 4000? I didn't see any keys for that) as was the case with my FX-8000G, when I replaced the batteries in that one my heart sank when I didn't see anything when I switched it on, until I got the idea to push up the contrast. That worked.

There should be a little contrast dial on the side. Same with the fc-200, and a couple other models that use that same chassis.

[vaklaff]

(08-08-2021 12:30 PM)johanw Wrote:  I tried it with a small, sharp philips screwdriver and pressed quite hard, that gave enough grip to get them loose. 2 new CD2032 batteries and the machine switched on immediately.

I was quite easy then :-) Congrats to getting it work.

The FX-4000P is one of the most beautiful calculators made, IMHO.

[johanw]

(08-08-2021 12:39 PM)Dave Britten Wrote:  There should be a little contrast dial on the side. Same with the fc-200, and a couple other models that use that same chassis.

Ah, yes, I found it. Thanks. I was looking at some mode setting like on the 8000G.

[grsbanks]

(08-08-2021 12:30 PM)johanw Wrote:  I didn't even have to tune up the contrast (is that even possible on a 4000? I didn't see any keys for that) as was the case with my FX-8000G, when I replaced the batteries in that one my heart sank when I didn't see anything when I switched it on, until I got the idea to push up the contrast. That worked.

I often found that replacing the batteries left all kinds of corrupt data in the 6000/6500/7000/80000/8500G series, including barely visible contrast. On those machines at least it's always a good idea to press the Reset button on the back, and more often than not, that rectifies the poor contrast.