Early
Electronic
Calculator		 Victor 18-1721 Calculator

Manufacturer: Victor
Model: 18-1721
Year: 1973
Form: Desktop
Functions: Scientific, user memory
Number of Digits: 14
Display Type: PPX
Display:Burroughs BR 16401 (Panaplex)
Logic Technology: LSI-6
Diodes: 30
Transistors: 42 (8*4+10)
IC Complement:Rockwell 10177 PA
Rockwell 10178 PA
Rockwell 10179 NB
Rockwell 10180 PA
Rockwell 10182 PB
Rockwell 15320 PC
(6 total)
Tech. Data Level: 2
Tech. Data Source: RE
Tech. Data Pages: 1
Tech. Data:Schematic (pdf)

Notes:
  • The eight display driver modules (part number 50210-40) each contain 2 digit drivers (1 transistor each) and 1 segment driver (2 transistors). See the schematic for more detail.
  • The small plunger underneath each key can be removed by twisting and pulling.
  • See the notes and log for the Victor 19-1421 regarding keyboard problems.

- Unit Log -

Serial Number: 4485-456
Year of Manufacture: 1973 (Integrated circuits stamped with 7128 to 7306)
Date of Receipt: Jan 2004.
Source: Received from DG for repair.
State upon Receipt: Good physical condition. Problems with display.
Current State: Fully functional (24 Feb 2004). Returned to owner 26 Feb 2004.

Date: 15 Jan 2004
Symptoms: No display upon power-up, eventually "0" lights up and other numerals can be entered and seen, except for "1".
Analysis: Display voltage rises from approximately 188V to 200V over a few minutes. Variation shows up on the middle of the three zeners of the H.V. regulator. Under external test, VZ of this zener varies but seems to max out at 51V.
Solution: Zener stack replaced with 91V,39V+24V,47V (1N4763A,1N4754A+1N4749A,1N4756A) giving voltages of V(-D)=-201V, V(-SC)=-154V after warm-up.

Date: 16 Jan 2004
Symptoms: Slight glow on 'd' segments when other segments in proximity to them are lit.
Analysis: Scope shows voltage on 'd' segment around -110V when off (should not be so negative). Measurement of clamp diode for 'd' segment differs from that of other segments. Presumably diode is slightly leaky.
Solution: Clamp diode for 'd' segment replaced with 1N4004.

Date: 21 Jan 2004
Procedure: 3 regulator diodes and pass transistor of 25V regulator replaced (measures 25.8V after replacement).

Date: 28 Jan 2004
Procedure: Conductive key pad for 'LOG' and multiply key loose, reglued.

Date: 28 Jan 2004
Procedure: Case and keyboard cleaned. Keycaps lightly machine buffed and polished.

Date: 24 Feb 2004
Symptoms: Initial "0" still slow to light up at power up, leading "1"s are slow to ignite for first minute or two.
Analysis: At power-up, V(-SC) (segment clamp voltage) is a little too low to permit reliable ignition.
Solution: Zener stack replaced with 91V,68V,43V (1N4763A,1N4760A,1N4755A) giving voltages of V(-D)=-203V, V(-SC)=-160V after warm-up.

Unit functioning well, except initial "0" still sometimes takes a second or two to ignite.


  Victor 18-1721
Calculators | Integrated Circuits | Displays | Simulations
EEC 		bhilpert