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

[clarke2001]

Hi, I am new here on this great site, I am a happy user/collector of HP and other RPN calculators.

Now I have a problem with MK-52. I was just repairing one (thx for the useful infos above). It was pretty quite hard, keyboard, ribbon cable, elko replacements etc. Now it works fine but, the K pre-button functions don't work at all. They produce the "famous MK-like" Error message. Only the K-0 (NOP) button doesn't.

It is not the matter of K button or other keyboard issue, because writing it in a program, the proper instruction code appears in program listing. For example: K-5 (3H) -> 32 i.e. sgn(). Running this tiny program, I got the Error message again, as in manual mode.

All other functions, operations, EEPROM clear/write/read are OK.

Does it make a sense ? Maybe I have a corrupted ROM ? Or is there any way to put in and run some diagnostic, repairing code ?

The machine is made in year '92. And i think not in Ukraine but maybe in Belorussia. There is no 2nd slot at rear side (on jebem's pictures colored yellow). Only the blue slot is built in.

An other issue is the power voltages: My machine cannot work with -15V, only at approx -13,5 V. The unstabilized outputs (-27V, -40V) are very, very depending of input power voltage. Lower batterie voltage makes higher outputs.

Thanks for reading this long stuff, any info, advise are welcome.

Laszlo

Update: 2015.08.23.

Problem solved. The machine (DC-DC converter and the unit) is somehow defective. I digged out another MK-52 (keyboard broken), replaced the electrolic capacitors in DC unit, and it works perfectly, the input (battery) voltage doesn't influence the output, but:

when I adjust:

-V2 -15V (pin6) -> IC logic circuits

the voltages are as follow, approx:

-V3 -33V (pin5) (instead of - 27 V) -> to the VFD display
-V4 -17V (pin8) -> to the -12V regulator for Ucc1 pin 12 and Gnd pin 4 of EEPROM KP1601PP1
-V5 -56V !!! (pin4) (instead of - 40 V) -> to the -33V regulator for programming voltage Upr pin 15 of EEPROM KP1601PP1

and the machine doesn't work after switch on

on my machine V2 must be set to - 13,5 V ( V4 = -15,5 V) for working at all, and to have proper V3 ( - 28 V), V5 (-43 V) values.

Production year '92 maybe explanation for that ?? who knows ...

I plugged the good PS unit into the other machine, but the K prefix functions are still resulting Error. Quite strange case.

But after all, getting out the repaired keyboard, ribbon cable of this, and using them in the older machine, now I got a perfect working MK-52, that counts.