Unusual non-HP RPN (red led display) to restore...


A few days ago I impulse-bought a calculator on eBay. It is an "Emerson E12" calculator. There was no detailed description, but looking at the photos I noticed it was RPN so I bought it - at 14 Euro it was cheap enough.
It arrived today, and it works when I power it with the included adapter. It's pure RPN, quite nice and feature-rich, made in 1975. I opened it, and it's quite clean inside, but I noticed that it's actually a re-badged Corvus 500! And I'm quite happy about that! :)

But it has a problem with the display: three segments are totally missing, and two more have a few "dots" missing. The display is made by hp (there's 1130-053 written on it). Is there something I can do to fix it? If not, is there somewhere to buy another - or a compatible replacement?

Second problem: there was some oxidation on the metal contacts for the batteries. I cleaned them the usual way, but one broke. What material should I use to rebuild it? Copper foil? Something else?

Third question (but this is unrelated): another calculator I'm restoring has (had) a foam pad between the keys and the domes. The foam has disintegrated with age. What can I use to replace it?

Fourth: right now I'm in the process of trying to restore several calculators... is it OK if I ask a lot of questions here? :)



I'm certain others will chime in with more useful advice, but I've seen 2 common types of LED failures on old calculators, both relating to bad electrical contact between the LEDs and the driver.

First, if the contacts are dirty/solder joint broken/wire or trace cracked, that would do it. Solderless HP Spice series machines had issues with this, the LED module (like everything else) was held against the PCB contacts by a piece of plastic and a couple of spring clips.

Second, it's possible for chemicals from degrading batteries to get inside the LED module and eat the bonding wires. You can see this by looking closely near the segments with the unit disassembled, you should see several tiny wires running to the segments. If any of these seem broken/missing/corroded, you're probably looking at replacing the LED module.


Congrats on your find. This is the first time i have heard of that brand, or any rebadging of the Corvus 500. Is it an exact copy as far as you can see?

Re your fourth question: Asking questions about repairing old calculators (especially hp & RPN) is one of the reasons for this forum's existence.


As far as I can see, it's an exact copy - I only have pictures of the Corvus, but it seems an exact copy of mine. And the motherboard of mine has the Corvus logo on it, that's why I thought of a mere re-badging.
And the display is an hp part! :)



Where was it made ? My Corvus 500 was made (assembled) in Hong Kong. Also, I assume you realize that you can operate it from a universal AC adapter @ 4.5 Vdc in the event you can't repair the battery connectors. I'm using 3 x 1.5V AA alkaline cells in mine.


It was "assembled in Hong Kong".
It came with its (working) power supply, that's how I've tested it - can't use batteries until I rebuild the contacts (if I ever will)! :)

I couldn't find anything online about it... (the brand is actually "Emerson Electronics").



I don't know if it's the same company, but Emerson used to make tube radios.


...and there's that other Emerson. There is a quote by him stuck right above my computer and in front of my nose. "Do the duty of the day". So i best be signing out and doing those roof drains.

btw, Cristian; Your duty is to fix that Corvus clone. You'll like using it.


I don't know if that's the same Emerson, the logo is different... Are you interested in a photo? :)


Edited: 23 Oct 2011, 12:28 p.m.




OK, I'll post a pic when I get home later today. I have to upload it to my own web space, right?



I don't know if it's the same company...

Emerson Electric is a large company that made all sorts of electrical stuff. Fans, power tools, radios, air conditioners...

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