Monroe 430 Calculator repair and cleanup

I man­aged to snag a Monroe 430 cal­cu­la­tor that was in good con­di­tion and a rea­son­able price. The Monroe 430 is 14 dig­it four-func­tion cal­cu­la­tor with mem­o­ry, per­cent, and a few oth­er extras. I have worked on a mod­el 425 and 420 in the past so I kind of knew what I was get­ting into, espe­cial­ly the lack of documentation.

Monroe 430 cal­cu­la­tor with 14 dig­its displayed
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Monroe 650 Calculator repair and cleanup

Welp, anoth­er cal­cu­la­tor tale of woe. This time it is a Monroe 650 cal­cu­la­tor found on eBay. The 650 is the top-end mod­el of Monroe’s 600 series cal­cu­la­tors. It is a 16 dig­it Nixie tube dis­play cal­cu­la­tor with addi­tion, sub­trac­tion, mul­ti­pli­ca­tion, divi­sion, square root func­tion, and two mem­o­ries. It oper­ates in fixed dec­i­mal or float­ing point modes, and has 5 chang­ing indi­ca­tors spaced every incre­ment of the base-10 expo­nent of three from the dec­i­mal point.
The price was right and includ­ed free shipping.

Monroe 650 cal­cu­la­tor after cleanup and repairs
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Digitronic‑M Calculator Repair

During my wan­der­ings on eBay I came across this 12 dig­it dis­play Digitronic‑M cal­cu­la­tor. It was an auc­tion list­ing start­ing at $0.99 with a real­ly low ship­ping cost, and the sell­er list­ed it as “works great!”. I put in a very low bid on it, not expect­ing to win it, but it turned out I was the only bid­der. That was the good part of the transaction.

Eico Digitronic‑M after cleanup and repairs
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Monroe 40 Calculator Refurbishment

An ear­ly hand­held cal­cu­la­tor from 1974, with a 10 dig­it Panaplex dis­play and recharge­able bat­tery.
As I con­tin­ue search­ing for Monroe 400 series cal­cu­la­tors, I came across this Monroe mod­el 40 cal­cu­la­tor at a rea­son­able price, with a few small issues.
Normally I don’t have an inter­est in hand­held cal­cu­la­tors as most are too new. This one caught my eye with it’s unique styling and 10 dig­it Neon Panaplex II display.

Monroe 40 hand­held cal­cu­la­tor side view
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Eiko Unitrex 1200M Calculator Refurbishment

Another bar­gain price pur­chase of an Eico Unitrex 1200M cal­cu­la­tor. This mod­el also uses the same CT5005 LSI cal­cu­la­tor on a chip IC as the APF Mark XII Calculator, but is note­wor­thy because of the rela­tion­ship of Eico with Cal-Tex Semiconductor, Inc., the man­u­fac­ture of the IC chip. The 1200M was the first cal­cu­la­tor to use a sin­gle LSI IC with inte­grat­ed mem­o­ry. It also has a beau­ti­ful 12 dig­it Neon gas-dis­charge display.

Eico Unitrex 1200M cal­cu­la­tor 12 dig­its plus memory
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Burroughs C 3207 Vintage Calculator

Well I just fin­ished work­ing on the APF Mark 1 cal­cu­la­tor so I was­n’t look­ing for anoth­er cal­cu­la­tor project right away, but I stum­bled upon this Burroughs C 3207 cal­cu­la­tor with sev­er­al issues for a price that was too good to pass up. And it’s a vin­tage 14 dig­it Nixie tube cal­cu­la­tor Built in late 1969.

Burroughs C 3207 Nixie tube cal­cu­la­tor after clean­ing and repairs
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