Radio Shack Model 65-115

Radio Shack introduced already in 1999 with its Model 65-115 a scientific calculator with 67 functions and a 12-digit display. This Model 65-115, introduced in 2006, features a two-line display and a whooping 241 functions. If the calculator does looks familiar to you - it uses the keyboard layout of the Casio fx-82MS and it's dozens of knockoffs. We assume that the fx-82MS is the most copied calculator ever...

Here at the Datamath Calculator Musuem we acquired the featured Radio Shack Model 65-115 calculator after learning that it reports with 9.000002051244 the same Calculator forensics result as the Qusure BA II Plus, an almost perfect copy of Texas Instruments' BA II Plus.

Disassembling the featured Radio Shack Model 65-115 with the Date code 06A07 and manufactured June 2007 in China reveals a very typical internal construction of the early 2000s, centered around a single-chip calculator circuit mounted in Chip-on-Board (COB) technology directly on a double-sided printed circuit board (PCB). The backside of the PCB features the contacts for the keyboard and LC-Display and power is provided by two small LR44 batteries.

Removing the small blob of epoxy resin protecting the chip of the Radio Shack Model 65-115 calculator reveals a microcontroller marked with EZ5A12 and manufactured by ELAN Microelectronics Corporation, a semiconductor company headquartered in Hsinchu, Taiwan. Die size approximately 110 mils * 100 mils / 2.8 mm * 2.5 mm. Die Photo courtesy of Sean Riddle.

Inspecting the PCB of this Model 65-115 calculator brought our attention to a small mark reading KC-S500, revealing Karce Company Limited in Hong Kong as Radio Shacks contract manufacturer.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, February 25, 2025. No reprints without written permission.