Early
Electronic
Calculator		 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:offline

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.

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.


  Keystone 2050
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EEC 		bhilpert