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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Power Designs D‑series display board update

After the acqui­si­tion of my Power Designs 5015D pow­er sup­ply, I real­ly want­ed to upgrade the dis­play mod­ule so that I had an extra dig­it of res­o­lu­tion. I already had a few ADC/LED meter boards left over from pre­vi­ous projects, but need­ed a dis­play board to pair with it.

Power Designs D‑series dis­play board Rev. 2.4
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