ELEKTRONIKA MK 61 display and keys dont work (Pictures)

[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.