Hi,
had the problem few months ago. Changed the battery and cleaned contacts and it went a while for a week or so. I had my tech change the battery clean the contacts but the problem persists.
According to test mode everything is ok and and hardware reset didn’t help.
What should I do next?
In what sense gets stuck?
Next step would be to replace the internal PSU if you’re tests are coming out ok
Yes, MnM mki or mkii? mkii did have a more reliable PSU at least.
After hardware reset it gets stuck at the Elekron logo.
How to change the PSU?
Mk2
You can attempt replacing with a PSU-2b.
Not guaranteed to resolve your issue of course, but it’s cheap and not invasive and if you still need to fix the components, you have an extra psu 
Or also if you have an OT or MD mkii, you can borrow one from them.
I would not buy any generic PSU from Amazon or the like, it’s never saving enough money to make it worthwhile.
MONOMACHINE MKII, MACHINEDRUM MKII, OCTATRACK MKI
Current Elektron power supply: PSU-2b. These devices were originally shipped with PSU-2. The PSU-2b power supply handles voltages of 100-240 VAC, 50/60Hz.
The power supply you want to use must meet the following specifications:
Voltage: 6 VDC Minimum Current Rating: 3 A Barrel Connector Size: 5.5 mm outer diameter, 2.5 mm inner diameter, 6 mm length Polarity: Positive center
Thanks for the info.