I am Chinese and I edited these photos for a local forum. So please ignore Chinese characters on the photos.
This method is available for casio fx-*es calculators. NOT MS or ES PLUS series.
Step 1: If You Are Lucky
The version is marked on the back of the calc. you can see a letter in a small circle which is at the top-right corner of the rectangle that has text in it.
If the letter is A, you are lucky.
Just open the calc, find the P4 jumper on board, fill the gap with pencil.
Then turn on your calc, see if there are 8 modes available.
If the letter is B, see the following, it is difficult to upgrade, but it is possible.
CAUTION: The success rate seems be VERY low. About only 20% can do it without experience. It is easier to do it with a magnifier.
It will mostly affect the display(too dim, strengthen ) if you fail.
or just not able to turn on.
TRY THIS AT YOUR OWN RISK
Step 2: Position the Chip
then place a ruler like the photo, there is about 1.2 cm from the reference to the chip.
mark a cross on the chip.
connect the reference to the destination then mark it on the bonding
Step 3: Dig the Bonding
keep the trace narrow.
you NEED a magnifier, or it is very easy to be broken.
The mode will switches to P- if you cut the line between the chip and the board. You can fix it with a pencil if you want to give up. but it isn't matter if you want to upgrade.
P- only have 3 modes, but it can do calculus, SOLVE/CALC, sigma, but no natural display.
Step 4: Change the P* Pin
clear the bonding on the chip until you can see the reflection of the chip.
ONLY need a little.
draw on the chip border with a pencil.
Step 5: Finishing
if it is P- or there is only 6 modes or 4 modes, try broaden the exposing length of the chip especially on right, then smear it again.
If it is P0 or P4 or P? with 8 modes available, you are done.
the keys are remapped as the 991, eg. the Abs key in 82 is CALC key in 991.