Elektronika MK-61 - today I ordered one NIB

[jebem]

(09-25-2014 02:47 PM)Francois Lanciault Wrote:  Yes I did, I opened the calculator and check with a voltmeter that the current was reaching the PCB. I also tried with a regulated power supply. For the power switch I tried by-passing it again directly on the PCB.
F.

Hi Francois,
Sorry to know about that issue on your MK-52 machine.

Probably the next step is to check the internal DC-DC converter power supply operation.
If the calculator VFD doesn't light up, probably the 27V line is faulty?

I think it is a good idea to use a oscilloscope to check the DC-DC oscillator section (you can borrow one from a friend or from a school, if you do not have one with you).
The DC-DC oscillator converter is a simple circuit with a few silicon transistors; one of them can be faulty; also check the electrolytic capacitors, one of them can be faulty as well.



EDIT:
Additional information on the DC-DC converter internal power supply

Both calculator models (Mk-52 and MK-61) takes the battery supply to generate a number of Negative output supply voltages for the electronics.
The battery Positive terminal is used as Ground as well.

MK-52 DC-DC power supply:

Common:
+BATT/GND (pin9) -> Gnd/+5V to IC's like EEPROM KP1601PP1 Ucc2 pin 24.

Input:
-V1 -BATT (pin7)

Output:
-V2 -15V (pin6) -> IC logic circuits
-V3 -27V (pin5) -> to the VFD display
-V4 -17V (pin8) -> to the -12V regulator for Ucc1 pin 12 and Gnd pin 4 of EEPROM KP1601PP1
-V5 -40V (pin4) -> to the -33V regulator for programming voltage Upr pin 15 of EEPROM KP1601PP1
~V6: 2.4VAC (pin 1 and 3) -> to the VFD display filament [Edit]

Note on the EEPROM:
KP1601PP1 == ER2401 (1024x4 bit)


MK-61 DC-DC power supply:

Common:
+BATT/GND (pin9) -> Gnd/+5V to IC's

Input:
-V1 -BATT (pin3)

Output:
-V2 -15V (pin4) -> IC logic circuits
-V3 -27V (pin7) -> To the VFD display
~V4: 2.4VAC (pin 1 and 2) -> to the VFD display filament [Edit]


The following attachment diagram shows the MK-52 four output voltage DC-DC converter power supply.