How to upgrade your fx-82es, fx-83es and fx-85es to a fx991

[pingouin]

Je suis surpris que personne ici n'ai aborde le sujet.
ATTENTION: ne marche que sur les vieux modeles A (c'est a dire avec un A dans un cercle au dos).

Voir ici:
https://www.thestudentroom.co.uk/showth ... p?t=557455

Pour resumer, souder le point P4 (et idealement couper tous les autres) donne toutes les options.

Je recopie ce que j'ai deja dit la bas:

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All, after a bit of experimenting, here is my take on it:
- You're only supposed to have a single P point shorten.
- By default, my fx-83ES (rev A) had P3 shorten. I assume this is true for all fx-83ES.
- If you also short more than one point, say you short P4 in addition to the default P3, the calculator is confused. Hence it will display the mode P?, and apparently unlock all functions. I didn't confirm this by shorting a point other than the suggested P4.

I found the following website:
http://hi.baidu.com/ecfan/blog/item/...a2eddd481.html

They tend to agree that by shorting P4 (or according to me, ANY other P point, although again I didn't test this hypothesis), the calculator is confused. They go on asserting that this could lead to long term damage and battery draining problems, although I'm doubtful about that. More interestingly, the guy suggests to cut P3 and P4 (if shorten), and short P0.

Now, since I have a soldering iron, instead of actually cutting the tracks, which I don't recommend, I just removed the solder I originally put on P4, removed the solder on P3 (put in factory), and shorted P0 (again with solder). And lo and behold:
- I have all functions unlocked again.
- The mode is now displayed as P0.

I would therefore suggest to everyone that this the "correct" route to take, although again, I can't say that shorting several P points and having the mode as P? is harmful in any way.

I further tried:
- Shorting only P7: mode is (unsurprisingly) displayed as P7, but you don't get all the modes, just like P3.
- Cutting ALL P points. In which case, mode is displayed as P-, and again you don't get all the modes.

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With my P0 soldered bridge, I tried to short every other point in turn. In each case, as I suspected, the mode displayed was P?.

However, I was wrong in that mode P? does not systematically unlock all 8 menu options. My findings are that by shorting the following P points in addition to P0 (I used pencil graphite for the tests):
- P1: only 3 menu options
- P2: only 3 menu options
- P3: only 3 menu options
- P4: all 8 menu options
- P5: 6 menu options (the usual 3 plus CMPLX, BASE-N and EQN)
- P6: 4 menu options (the usual 3 plus EQN)
- P7: only 3 menu options

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I also tried P0+P3+P4, and I still get mode P? and all 8 menu options, so it seems that as long as P4 is shorted, it doesn't matter which other points are shorted. So something to test by someone: what if you short P4 only and cut everything else? And if P4 gives the 8 menu options, what is the difference between modes P0 and P4? And what is the difference between modes P1, P2, P3 and P7 anyway?