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Got this machine in a lot of other models from a flea market.
This looks like one little brother of the more powerful Casio fx-4000P.

Made in mid 80's. No way to know a date for sure as there are no date codes in any internal component.

Forensics result as displayed: 9.000015718
(Degrees mode. 9 sin cos tan atan acos asin)
I didn't try to get the extra digits, hence the different value from the rskey reported value.

[Image: Casio_fx-3800P_002.jpg]

Enter BaseN Hex mode and get the 2's complement of FFFF
Result: FFFF0001

Then go to BaseN Dec mode.
Result: -65535

[Image: Casio_fx-3800P_003.jpg] [Image: Casio_fx-3800P_004.jpg]

Low profile pocket machine typical of Casio of that era.
Single 3V CR2025 battery cell.
Undo the six steel screws to remove the back cover.

[Image: Casio_fx-3800P_007.jpg] [Image: Casio_fx-3800P_010.jpg]

Back label contents:
Casio fx-3800P
DC 3VDC 0.0005W
Use Battery 3Vx1
Made in Japan
Casio Computer, Ltd.

Declared power consumption of just 0.0005W (500μW and a current of 167μA). I didn't check these readings.

[Image: Casio_fx-3800P_009.jpg]

The On-Off switch will get lose after removing the back cover and should be stored for later reassembly.
Undo two extra screws to remove the PCA.
The LCD display assembly is attached to the PCB and it is not glued to the front panel. It is maintained in place by a foam that is pressed by the back cover.

One interesting note on the LCD assembly: The LCD itself is glued to a heavy metal frame. Not sure what was the engineering reasons behind this design choice. Most probably to give extra rigidity and protection, while giving the calculator more mass/weight for a more customer satisfying experience ?

[Image: Casio_fx-3800P_011.jpg] [Image: Casio_fx-3800P_012.jpg] [Image: Casio_fx-3800P_013.jpg]
No date codes on any component.
No identification in the SoC processor either.
The PCB reference is: G937-1 3

[Image: Casio_fx-3800P_014.jpg] [Image: Casio_fx-3800P_015.jpg]

Only two passive components can be identified.
One SMD resistor marked as "224" (220000‎Ω = 220K‎Ω).
One legacy pass through tantalum polarized capacitor marked as "J335" (3300000pF = 3.3μF)

[Image: Casio_fx-3800P_017.jpg] [Image: Casio_fx-3800P_018.jpg]
I have one or two of them too. Nice Calculator.
I bought one of these new back in the 80s!

It's packed away in its box somewhere - still haven't gotten around to unpacking everything since the last house move - and that was 6 or 7 years ago!
Only few Casios of that eara offered programmability *and* fractions, among them the fx-81p and the fx-3600p. I always wondered why fractions have been omitted from models like this one or even the french fx-81p Plus. Were there any bugs?
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