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

[Adalin]

So

I have a mk-52 that seems to have a broken eeprom, at least I think its broken
I cant save anything to it in any case

I opened up the unit and measured the output of the voltage converter and all numbers where in the 5% range, I replaced the capacitors anyway and adjusted the voltage, but the eeprom still does not work

when I got the unit some time ago I wrote some programs and saved them to the internal eeprom, but I got some strange effects and thought that maybe I did something wrong, but I have tried many times now and it just doesn't save anything.

I start with clearing the memory and then I write the program and write it to the memory, then I load the program again, and its gone...

Has anyone replaced the eeprom chip in one of these calculators? I bought some replacement eeprom chips and some replacement VFD screens just in case, so I will try to replace the eeprom when they arrive.

or is it something I have missed?

its a later unit, from 1991. I got a PRB-4 external rom and it works fine when I load programs from it