LogicData TA-9 Calculator

Manufacturer: LogicData
Model: TA-9
Year: 1972
Form: Pocket
Functions: Basic four, constant, memory
Number of Digits: 9
Display Type: VFI
Display:no-id no-id
Logic Technology: LSI-2
Diodes: 13
Transistors: 11
IC Complement:* EC14**
* *
Batteries: 4 AA NiCd
Power Connector:* VDC, special
Tech. Data Level: 1
Tech. Data Source: RE
Tech. Data Pages: 1
Tech. Data:Schematic (pdf)

An early American-made pocket calculator. The model is based around an unidentified two-IC LSI chipset (the ICs were originally labeled but were not discernible when received). Sadly, one or both of the ICs in this unit seem to have failed, and the unit is not functional. Too bad, as it is an early and rare model.

The unit came with a promotional brochure from Standard Oil. See the family gathered around the kitchen table looking with excitement at the amazing calculator. Yours for only $8.50 a month for 12 months on your Standard Oil credit card.



- Unit Log -

Serial Number: 000218
Year of Manufacture: 1972 (IC stamped with 721*)
Accessories: With zip case, AC wall wart, manual, Standard Oil promotional brochure.
Date of Receipt: 18 Sep 2015
Source: doorstep.
State upon Receipt: 4 NiCd cells still present. Some battery corrosion on PCB. IC identification disappearing, appears to be from battery off-gassing. Only discernible lettering is EC14 on one IC and 721 on other. This simply wiped off. Otherwise good condition.
Current State: Not functional. One IC of chip-set appears to have failed (2020 Feb). Needs cleaning (Sep 2015).

Date: Sep 2015
Procedure: Batteries removed, some cleaning.

Date: 2020 Jan
Procedure: Some cleaning and scraping of corrosion on PCB.

Date: 2020 Jan
Symptoms: No display or activity.
Analysis: Clock not working. Two transistors and one cap removed and substituted, clock now works. Simple junction measurements of transistors are OK, but they don't work in-circuit.

Date: 2020 Jan
Symptoms: Power supply failing.
Analysis: Two switching transistors measure bad, replaced with 2N2222. V-6 is low, around 5.7V, zener V is ~6.3V rather than rated 6.8V. Diode added in series to zener, V-6 now ~6.3V. V-29 series-pass transistor failed CE-short after shorting V-29 to gnd, replaced with 2N4402.

Two 470K digit pull-downs replaced.

Digit scan signals and other derived clock signals (sourced in U2), are present but no discernible activity from U1. Connections to IC pins measure OK. U1 appears to have failed.

Date: 2020 Mar
Analysis: During further attempts, digits clocks phiD0::D6 are lost, phiDS remains good. Some more cleaning of corrosion around PCB. Display board separated from main PCB, unit exercised without display attached. No improvement.

  LogicData TA-9
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