I needed a new calculator and the way I see it, if you're gonna buy a new calculator,  why not do it with some style? That's how I ended up getting a vintage soviet calculator from ebay, the mighty Elektronica MK-61! There is just something about that old school green VFD screen (Vacuum Fluorescent Display) that appealed to me. I also like vintage stuff like that, not only do they look unique but you can almost feel all the history contained within them. It worked fine for a year and a half and then suddenly it would not turn on. I tought the batteries might be dead but the issue remained after replacing them with fresh one. I managed to have it turn on once or twice but it would sometime display a few 0 or it would flicker and not work. Everything was pointing to a defective slider switch and it wouldn't be surprising for a 20 years old calculator. So it was time to crack it open and see what make it tick (or no tick in this case)! I must say I was pretty excited about opening it up because I find Soviet technology fascinating with their differents looking components and they would oftentime do things in a completly different way than what we're used to.     Insted of having a sticker like most calculator nowaday, the information was molded on the back. We can see that this particular unit must have been sold in the last years of the Soviet Union and that it used to cost 85 руб (rubbles).      The calculator case is held in place with plastic snaps and one flat head screw located under the battery cover. First unusual details, the screw hole was wax sealed and stamped with the Electronica logo  effectively playing the role of a warranty seal sticker that we are used to see nowaday. Unfortunatly, I damaged the seal before thinking of taking a picture of it so I wont be able to show you for now but you can see the green wax residue around the screw hole. Once you have managed to separate the two half of the casing, you will gain access to the PCB. It is held in place not by screws, but with six plastic clip.  You can free the circuit board squeezing the plastic case on the side while pushing the PCB up. You can already see right away that this is no ordinary piece of electronic. The resistors do not have the usual colored strip and I have personnaly never seen chip like the one found in this calculator. They look like SMD IC but they do not seem to have any silicon casing. The closest to this I have encounter are glob top, those cheaply produced chips whose core are soldered directly to the board and then protected by a drop of black epoxy encapsulant. This is like a weird hybrid of those two type of package. A quick continuity test with a multi meter showed what we were already suspecting, the inside of the power switch did not seem to make contact as it should when you would switch it to the ON position. We need to replace it, but with what model of switch? The thought of putting a different looking modern switch in such an awesome piece of vintage electronic made me cringe so I decided I should try to locate the original part. Considering that those part were built in the former Soviet Union, it should be easier said than done but I know that there seem to be a lot of NOS (New Old Stock, old part that were never used) Soviet component coming from country that used to be part of the Soviet Empire. I know that it is where most nixie tube come from so I figured I might get lucky. So I needed to figure out the model of the switch. Well, if you take a closer look at the switch, you will see Russian marking ''ПЛ-9-2'' which according to my quick search mean ''PD-9-2''. A bit of eBay searching and I was lucky enough to find a Ukrainian seller who seemed to have a bunch of them still brand new listed as ''Military switch PD-9-2''. He would only sell them by lot of 20 but it was cheap enough that it didn't bother me too much. Once I had the precious switch on hand, all that was left to do was de-solder the old one and replace it with the new one. Turn out it was easier said than done. You see, when you apply heat to the anker of the switch, it get diffused through the metal shielding making it much harder to melt the solder and even using de-soldering wick/braid was tricky because the pin hole are fairly small so it is hard to suck all the solder up. You also have to be a bit more careful about solder ball and solder splatter because this board has no protective mask and all the trace and contact are exposed making it much more likely to create solder bridge and such if you are not careful. It proved to be quite tricky to de-solder the old switch and I was worried of using my hot air soldering iron to remove it as the PCB is quite old and would probably not react well to being expose to very high temperature. So I decided that the best course of action was to carefully cut through the metal shielding. Normally, it wouldn't be the best of idea as it could cause too much stress on the solder joint and you risk of tearing of a pad or a trace but I felt it was less risky than over heating it while trying to de-solder it with hot air. So I carefully cut through the switch using a wire cutter.    Once the switch is sectioned like that, there is less place where the heat can transfer and all you have to do it push the pin down and clean down the pin hole after. This again proved more difficult than it should have been. I didn't have a choice at this point and had to use hot air iron to properly clean the pin-hole enough that I could insert the replacement switch. I actually had to replace the switch again as it wouldn't work properly. I supposed the switch got damaged by over exposure to high temperature (my hot air iron) or it was not seated properly. At this point I felt pretty dumb to be somewhat struggling with such an easy job when I am used to work with very tiny TSOP package! Good thing I was forced to order more than one switch. Did a quick test and it seemed to be working. All that was left to do was to re-assemble the calculator. This is a pretty interesting calculator, at first I couldn't figure to how to use it and couldn't even manage to do a simple addition. It was completly puzzling! Not liking being beated by a machine,I tried to figure out by myself for a few days before giving up and going to find more information online. It turn out that Soviet calculator were programmed to make calculation using Reverse Polish notation (RTN) where operator need to follow its operands. So in order to 5 + 3 on this calculator, you can't enter that way. You would need to press 5, then on the B↑ button to enter your second value and then finaly press on the - sign to get your answer. No wonder I couldn't figure it out, it is completly counter-intuitive for someone used to regular calculator. I wasn't aware of it when I bought it (unresearched impulse buy :) ) but it is also a fairly advanced calculator which contain memory space that can be used by the user to store custom program and sequence and even has a plug to connect it to run it without battery which was fairly surprising for soemone who grew up with regular North American consumer calculator. If it sound interesting to you, I suggest reading Alfred Klomp's in deph and pationnate article on how to use, program and hack the MK-61 (http://www.alfredklomp.com/technology/mk-61/). This is a fairly heavy read but it is quite fascinating and chock full of information about the MK-61.Twitter (function(d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) {return;} js = d.createElement(s); js.id = id; js.src = "//connect.facebook.net/en_GB/all.js#xfbml=1"; fjs.parentNode.insertBefore(js, fjs); }(document, 'script', 'facebook-jssdk'));{lang: 'en-GB'}