CASIO fx-5500 Scientific Calculator: The 1st "C.A.S." pocket calculator?

[jebem]

Tear down.

Back cover.
Power supply: 6VDC, 0.01W




Serial number suggests a date of 1986, February (6B).
Removing the aluminum back cover by undoing the two screws reveals the metallic sliding battery cover.




Removing the inner plastic frame by undoing eight self taping screws. Lift it at the battery side first, then use a plastic pry tool to unlatch the remaining sides leaving the display side to the end.
Note the grounding/shielding spring at the lower left side, interconnecting the front face plate and back cover to the circuit common ground.




The PCA is free to be removed. Lift it on the battery side first, then gently pull the display assembly to remove it from the front cover bed.




Unfolding the display flat cable to uncover the main PCA components:

• Hitachi HD61747B32 6B 23 HM47B-32 Processor (1986)
• Hitachi HD61747B33 5M 13 HM47B-33 Processor (1985)
• NEC D1004G (uPD1004G) NM390 6527KK 4K 4-bit words or 2KByte SRAM memory (*)
• Toshiba 4071BF 86 10HB CMOS Quad 2-input OR gates
  

(*) Can't find information on the NEC uPD1004G IC.
However, Kyoro's Room Blog documents the Casio PB-770 internals and we know that it uses four of these chips for a total of 8KByte of SRAM memory.

The Hitachi HD61747 processors are used in several Casio models, only changing the firmware code. For example:

• fx-5200P:
  Hitachi HD61747B16
  Hitachi HD61914C 1KByte static RAM
• fx-4000P:
  - Hitachi HD61747B38
  - HD61914 8kbit static RAM
• FC-200:
  - HD61747B55
  - HD61914 1KByte static RAM.
• PB-120:
  - HD61747B57 9L 13
• PB-500:
  - HD61747B05 5K 13
  - HD61747B06 5H 13
• PB-770:
  - HD61747B13 5C 13
  - HD61747B14 5C 13
  

Membrane keyboard using rubber keys and painted labels.
Not the best solution but the painting was good and it never fails to register a key.