Keystone 2050 Calculator

Manufacturer: Keystone
Model: 2050
Year: 1974
Form: Pocket
Functions: Scientific
Number of Digits: 8
Display Type: PPX2
Display:Burroughs BR 09250 M (Panaplex II)
Logic Technology: LSI
Diodes: 47
Transistors: 16
IC Complement:Rockwell 15473PA (aka 90128)
Batteries: 2 AA NiCd (1.2V each)
Power Connector:7.4 VAC, sub-mini audio
(alternate/no batteries: 3 to 5 VDC, + tip)
Tech. Data Level: 2
Tech. Data Source: RE
Tech. Data Pages: 1
Tech. Data:Schematic (pdf)

A rather rare early scientific pocket calculator. Unfortunately, this unit is non-functional, seems to be a non-repairable fault with the calculator chip.

- Unit Log -

Serial Number: C248340
Year of Manufacture: 1974 (IC stamped with 7422, display with 7416.)
Date of Receipt: 07 Jul 2001
Source: GT Fraser thrift store.
State upon Receipt: Fair physical condition, some rust stains inside, seemingly from something spilled in it. Erratic display, segment a does not work.
Current State: Non-functional (29 Sep 2001).

Date: 27 Sep 2001
Procedure: Cleaned.

Date: 28 Sep 2001
Symptoms: Segment 'a' does not light up.
Solution: PCB trace near segment 'a' pin open due to corrosion. Cleaned and resoldered, segment now functional.

Date: 28 Sep 2001
Symptoms: Erratic display.
Solution: Contact between display and pin for digit 1 open due to oxide buildup. Cleaned, unit now functional. Seemingly, the lack of load on the digit pin upset some other aspect of the logic.

Date: 28 Sep 2001
Symptoms: After a while of operation, unit slowly degraded: first occasionally not responding to keypresses, then key '2' would result in pi in the display, then a non-sensical display upon power-up and a blank display after pressing any key.
Analysis: Voltages and such all seem OK. Presumably the IC has developed a problem.

Date: 2020 Feb
Analysis: Unit powered up, voltages good. Most digits illuminate, with oddball segment configurations. Digit scanning is functioning, digit cycle is 3.6 mS. Many operations result in the digit scanning stopping (display blank), sometimes restarting after a second or so. However, pressing the PI key does present a "3" in the MSD, and pressing the +/- key alternates the negative sign in the display. Voltages on IC pins seem sensible.

  Keystone 2050
Calculators | Integrated Circuits | Displays | Simulations