ELEKTRONIKA MK 61 display and keys dont work (Pictures)

[lechuck]

Hello, my English is not very good, I hope you understand me.

A few months ago I bought a calculator Elektronika MK 61, after a few weeks began to fail the 2nd digit but soon he returned to run the digit, but increasingly took longer, but one day that stopped working and with it the following keys: "П→X", number "6" and "/-/"
The only way I can get all the digit is by simultaneously pressing key "6" and then another key, then i can see all the digits on the calculator.

Here some pictures:
   
   
   

[jebem]

(08-06-2015 12:16 AM)lechuck Wrote:  A few months ago I bought a calculator Elektronika MK 61, after a few weeks began to fail the 2nd digit but soon he returned to run the digit, but increasingly took longer, but one day that stopped working and with it the following keys: "П→X", number "6" and "/-/"

Hi, welcome to this forum.

Are you using batteries or the AC adapter?

The AC adapter can create issues on the calculator.
When using it, first plug the adapter to the calculator and only then you may connect the adapter to the AC outlet.
This is necessary because the adapter power is not regulated.

Also, after powering off the calculator, always wait at least 30 seconds before powering it on again!
This is related to the dc-dc converter switching power supply operation inside the calculator.

These two procedures will protect your calculator from being damaged due to over voltage.
And these are documented in the calculator users guide (in Russian language).

In you case, I would open the calculator and check for liquids in the mainboard and keyboard areas.

You my find more information here.

[lechuck]

Hi thanks for the advices, i'm using batteries, here some pictures of MK 61 opened.

   
   
   
   

[TASP]

Oh my.

[jebem]

(08-06-2015 01:07 PM)lechuck Wrote:  Hi thanks for the advices, i'm using batteries, here some pictures of MK 61 opened.

Ok, if you can remove the board from the front cover, you may be able to inspect the keyboard area t make sure it is clean of any dirt or signs of liquids.
I use isopropyl alcohol to do the cleaning and let it dry for 15 minutes at least.

The symptoms you describe can be related to dirt/moist in the pcb, or else the calculator have a defective IC probably caused by incorrect power supply voltages.

After making sure the pcb is clean, you may use voltmeter to carefully take some readings from the dc-c converter to make sure the correct supply voltages are being generated.
An oscilloscope is very handy as well, to read the power supply lines noise.
The usual suspects are the electrolytic capacitors that after some years without being used lose their capacitance or get dried.

Or you may just assume that the original electrolytic capacitors are defective (chances are that they are), and just replace it with new ones of the same capacity value and chose a higher working voltage.

If you decide to replace the caps, great care is needed to remove the old ones from the PCB.
Good solder and unsolder skills are required in order to not destroy the pcb copper traces that are kind of fragile in these calculator models.

[lechuck]

(08-07-2015 10:32 AM)jebem Wrote:  

(08-06-2015 01:07 PM)lechuck Wrote:  Hi thanks for the advices, i'm using batteries, here some pictures of MK 61 opened.

Ok, if you can remove the board from the front cover, you may be able to inspect the keyboard area t make sure it is clean of any dirt or signs of liquids.
I use isopropyl alcohol to do the cleaning and let it dry for 15 minutes at least.

The symptoms you describe can be related to dirt/moist in the pcb, or else the calculator have a defective IC probably caused by incorrect power supply voltages.

After making sure the pcb is clean, you may use voltmeter to carefully take some readings from the dc-c converter to make sure the correct supply voltages are being generated.
An oscilloscope is very handy as well, to read the power supply lines noise.
The usual suspects are the electrolytic capacitors that after some years without being used lose their capacitance or get dried.

Or you may just assume that the original electrolytic capacitors are defective (chances are that they are), and just replace it with new ones of the same capacity value and chose a higher working voltage.

If you decide to replace the caps, great care is needed to remove the old ones from the PCB.
Good solder and unsolder skills are required in order to not destroy the pcb copper traces that are kind of fragile in these calculator models.

Thank you very much ¡¡¡ the problem was solved by cleaning with isopropyl alcohol as you indicated and they have returned to work digits and damaged keys
Have a good one.

[TASP]

Not relevant to this repair job, but some years ago I used an aerosol degreaser product (sorry, don't recall the name) on a membrane keyboard in a restaurant kitchen on their waitress call light keyboard.

The keyboard was indeed, NASTY.

However, the instant the product touched it, not only did it dissolve 10 years worth of accumulated crud, it also liquified the keyboard.

Totally.

I've tried to be much more careful about such things since. I offer this experience in the hopes of saving more innocent keyboards in future.

[jebem]

(08-07-2015 06:45 PM)lechuck Wrote:  (...)the problem was solved by cleaning with isopropyl alcohol as you indicated and they have returned to work digits and damaged keys
Have a good one.

Glad to know that you manage to fix it.
Please keep posting your findings here on these Russian calculators.

And as TASP mentioned above, great care is needed to not destroy the plastics and labels from the keyboards when cleaning it.
On some calculators, even isopropyl alcohol can be dangerous.
Isopropyl alcohol is safe to clean the PCB (printed circuit board) and electronic parts only.
To clean the keyboard keys and face plates I usually use just warm water, a soft manual dishwashing detergent and a soft brush.