Unisonic LC 224CK Check Master

Date of introduction:  1981 Display technology:  LCD
New price:  $21.99 (SRP September 1981) Display size:  8
Size:  2.7" x 6.0" x 0.25"
 69 x 152 x 6 mm3
Weight:  2.0 ounces, 58 grams Serial No:  
Batteries:  2*LR54 Date of manufacture:  mth 09 year 1983
AC-Adapter:   Origin of manufacture:  Taiwan
Precision:  8  Integrated circuits:  Sharp LI3329MT
Memories:  1    
Program steps:   Courtesy of:  Ken H. Meine

Unisonic entered the market of Checkbook Calculators with the LC 262 in 1979. It features Account Manager functionality with three permanent (till you remove the batteries) Memories and started a very successful product line. We discovered as of now ten different family members:

1979: LC 262, 3 Memories, Credit Card size
1981: LC 262CK, 3 Memories, Credit Card size
1981: LC 263CK, 3 Memories
1981: This LC 224CK, 1 Memory
1982: LC 224CKE, 1 Memory, Pen
1983: LC 224CKM, 1 Memory, Pen
1983: LC 223CK, 1 Memory, Credit Card size
1985: LC 225CK, 1 Memory
1987: LC 266CK, 3 Memories, Taiwan
1988: LC 226CK, 1 Memory, Taiwan
1990: LC 226CK, 1 Memory, Thailand

Dismantling the featured LC 224CK manufactured in September 1983 in Taiwan reveals a clean design centered around a Sharp LI3329MT single-chip calculator circuit soldered on a double-sided printed circuit board (PCB) and powered by two small LR54 batteries. Learn how to decipher the 538A date code on the pictured Sharp chip.

Don't miss the LC 224CKE sporting a NEC uPD1832G chip in an otherwise identical package. Obvious differences are:

NEC uPD1832G [ON] and [CE/C] keys, display indicators left-hand side
Sharp LI3329MT [ON/C] and [CE] keys, display indicators right-hand side

We noticed these differences with the APF Electronics 3552CK and Enterprex MC-2717, too.

Inspecting the PCB of this LC 224CK manufactured in September 1983 brought our attention to a small mark reading 310S-10, most likely a reference to Type 310, Sharp LI3329MT and Revision 1.0 of the design (schematics and layout).

Please find an overview of the PCB-Marks we discovered so far on Account Manager calculators.

In addition did we notice on the PCB of the LC 224CK two small jumpers to select between:

(MR) Checkbook Calculator: [BAL/MR] doesn't clear the Memory
(MRC) Standard Calculator: [MRC] does clear the Memory

This interesting feature allows the use of the same PCB design for both "Standard" and "Checkbook" calculators.

Learn more about single-chip calculator circuits used in Account Manager Calculators.

Don't miss the Corvus CheckMaster introduced by Mostek already in 1975. This rare product retains the balance of your memory even when shut off but uses power-hungry electronics.

If you have additions to the above article please email:

Joerg Woerner, January 4, 2020. No reprints without written permission.