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Elektronika MK-52: The MK-61 big brother?
10-28-2014, 06:07 PM (This post was last modified: 10-28-2014 06:18 PM by jebem.)
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RE: Elektronika MK-52: The MK-61 big brother?
Repairing the DC-DC converter power supply:

I couldn't wait, could I?
My flight is 5 hours away and I'm still at home doing this nice hobby of ours... I guess it is time to start packing now.

Replacing the defective capacitors:
So, I just took the capacitors that I had at hand, and have selected these Jackon brand Low ESR 105c high temperature electrolytic capacitors able to cope with harsh environments and working nicely in switching power supplies as this one.
It should be more than enough for the job.

One word of caution for those who are whiling to do this repair as a diy hobby:
The PCB is double face and fragile, so use a small thin tip but potent iron solder to melt the solder joints in order to remove the components without bringing the PCB copper traces attached to the component leads.

I decided to replace all four capacitors with new ones, despite the fact that the two original 5uF are good.

After connecting a 6VDC power source, have powered ON the MK-52 and voila, it works!

[Image: mk52_028.jpg] [Image: mk52_029.jpg]

Voltage adjust procedure:
However the output voltages were off the mark, so I had to adjust it to the correct values.
I have connected a Voltmeter between the +Vbatt and pin 6 of the DC-DC converter and adjusted the potentiometer to read -15VDC.
Then check the other DC output voltages - they should be correct within +/-5%.

The current consumption is about 95mA, which is average for this kind of machines.

[Image: mk52_030.jpg]

Checking the DC-DC oscillator waveform:

Just for fun of it, I checked the switching oscillator wave shape.
My frequency meter is dead, waiting for a new set of NiCd batteries (Fluke 1920A), so I have used my vintage Centrad scope to estimate the frequency as well.

The period is about 14uS (71KHz) at 15Vpp, which is not far away of what the Elektronika is showing in the MK-61 schematics (I couldn't find this information for the MK-52).

[Image: mk52_031.jpg]

Assembling all together and initial RUN mode tests.
It looks good.
(I'm leaving the EEPROM testing for later):

[Image: mk52_032.jpg] [Image: mk52_033.jpg]

[Image: mk52_034.jpg] [Image: mk52_035.jpg]

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RE: Elektronika MK-52: The MK-61 big brother? - jebem - 10-28-2014 06:07 PM

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