Elektronika MK-52: The MK-61 big brother?

[ijabbott]

The display pin next to the 'VL1' text looks like it hasn't been soldered to its pad.

[Daniel.]

Hi there.

I took advantage of this gloomy afternoon to unclog the metallic holes.

A varnish has been passed over the integrated circuits and hinders cleaning.

What product to use to remove it around the metallic holes ? Acetone ?

Thank you.

[cruff]

(05-08-2020 08:47 AM)Daniel. Wrote:  Hi there, yes, the glass envelope of the display is broken.

You might be able to repair this. I'm assuming it might be too hard to fuse a new glass evacuation tube to the existing module without damaging it beyond repair, but possibly some vacuum compatible epoxy might suffice if you have access to a vacuum pump. I don't know offhand what sort of vacuum is required for a VFD to operate.

[jebem]

The VFD display is available as a spare part from Ukraine, the country where those calculators were made during USSR era and after that a few years more.

eBay lists several sellers, some offering them at around one to three USD each plus s&H. I bought some of those a couple of years ago and paid around four USD for shipping.
Look for "ILC2-12/8L VFD Display Nixie Tube for Calculators Electronika MK-52 MK-61" and you will find several offering.

The keyboard will not have any positive action when pressing the keys, no matter what kind of foam I used. This seems to be a characteristic feature of these MK machines.

To clean the PCB as well the enclosure parts I use warm water and dish detergent, and a soft brush.
Let it dry for 24 hours, preferably close to a window where it can get some mild heat, but avoid to expose the plastics of the enclosure to direct sun.

After that the PCB receives a proper cleaning with IPA applied with a soft brush.
I never use IPA on the cover, as the labels may be erased.

I never use acetone or other aggressive chemical reagents on electronics like these, so I can't comment on that.

Edit:
For IPA, see https://en.m.wikipedia.org/wiki/Isopropyl_alcohol
It is easy to find it in plastic bottles, 1000ml or 2000ml, in hardware stores.

[Daniel.]

New condensers just arrived, immediately soldered. :-)

Still waiting for the VFD.

Regards.

[Daniel.]

Hi there, I'm looking for the schematics of the expansion ROM.

Regards

[Daniel.]

Finally the VFD is arrived :





I put in place on the PCB and set the height over the PCB at about 2mm :





After soldered the legs I turn on the calculator, no magic smoke but display doesn't work properly with many dots and/or comma ...



Fortunately it was only a short circuit due to a small piece of solder which shorted two legs of the display. :-)

[jebem]

Nice photos for a successful repair, Daniel.
Thank you for sharing your work here.
Cheers,
Jose

[Daniel.]

Hi, thank you Jose.

Regards

[Paul87]

Luckily bought working MK-52. It was not easy finding as soviet programmable calculators are almost disappeared from second hand market even in Eastern Europe.
These items were expensive and soviet people were very practical so it was rare to have it in family except for some students and engineers.
And still it were more common than early personal computers (ZX Spectrum or similar clones). Folks loved to enter gaming codes from technical magazines and play with Mk-61 or MK-52.
There still exists great web site with game codes http://lordbss.pp.ru/pmk.html

I tried to make roll the dice algorithm and here it is:
Kсч B↑ 6 X B↑ 1 + B↑ K[x] C/П
Code check sum: 3L 0E 06 12 0E 01 10 0E 34 50
After entering prog. and returning to auto mode, X register has to be filled with random number from 0 to 1, e.g. 0.3521452 (for making randomised numbers sequence). And then to clear counter B/0 and start prog. C/П. Repeating roll the dice: B/0 C/П.

(01-24-2020 07:32 PM)linuxslate.com Wrote:  I have written a simple proggie to roll a dice using a super simple implementation of a "Middle Squares" psuedo random number generator, which creates seeds for the internal psuedo random number generator.

Willing to share here if there is any interest.

Is your algorithm similar? I saw different implementation in Youtube where code loops from 1 to 6 continuosly and program has to be stopped manually after random time.

Tried to write code to EPROM. I found that it not worked with plugged in AC adapter nor used batteries. After replacing AA batteries (1,5V x 4) with fresh ones, were able to clear and rewrite EPROM.