Nixie Tube Calculator - 1972 Monroe 620 - Repair and Demo

After a long wait I've finally got myself a Nixie Tube Calculator (or more correctly, a calculator with a Nixie tube display - it doesn't calculate nixie tubes!!!). The Monroe 620 was made somewhere around 1972 - I think there's a date code of November 1971 on the Texas Instruments chips, so that would put the calculator into 1972 or thereabouts. This calculator and others in this series, was actually made by Canon and placed in a Monroe case.

The calculator was in a pretty bad state when I got it, the case was badly damaged, the circuit boards were filthy and some (most) of the capacitors were reading incorrect values. Once everything was cleaned, some components replaced and the case repaired, the calculator started playing up - the problem eventually being traced to a bad via on the keyboard PCB.

The Nixie tubes in this machine are marked as:
JRC
B-5755
K114E2
Made in Japan

If you're interested in seeing some other vintage calculator repairs and demos, I'll put a few links below:
Hitachi KK561 repair    • Vintage Calculator Repair - 1972 Hitachi K...  
Hitachi KK561 Demo    • Vintage Calculator Repair - 1972 Hitachi K...  
Friden 2002 repair and demo    • Vintage Calculator - Singer Friden Model 2002  
Madas 20LZVG repair and demo    • Calculating Machine Repair and Demonstrati...  

If you want to see some beautiful nixie tubes being made, head to Dalibor Farny's channel    • The Art of Making a Nixie Tube  

Start 00:00
First Look 00:37
Power Supply 01:16
Pre Testing 02:55
First Test 04:14
Case Repairs 05:00
Power Plug 06:10
Keyboard Fault 06:30
Demo 08:39
Divide by Zero 14:45
The Nixie Tubes 15:17
Outro 16:44

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Outro Music
"As Yet Untitled"
by GrumpyTim (available to download from GrumpyTim's Bandcamp page)
https://grumpytim.bandcamp.com/

http://www.grumpytim.com