My friend, who's an electronics boffin (besides being a busy musician) finally had time to look into my shaky NL3s.
So here's what we found. (cheap, working and easy fix follows!!)
First of all we needed to reproduce the failure. A vacuum cleaner did the trick. When (turned on and) plugged into the same socked, the Nord Lead rebooted consistently :-)
It turns out there is a slight design flaw on the PSU board of the NL3. The board delivers 12V (for analog bits), 5V and 3V3 (for digital bits and the 100s of LEDs).
All three supplys are build in a very standard way, however the 3V supply lacks the reservoir capacitor that you'd usually find. The capacitor helps smoothing the voltage, and also counterworks 'brownies' on the mains supply. The PSU actually delivers 3V ok-steady, but measuring before
the final voltage regulator reveals a significant voltage ripple.
The fix we suggest below made both my Nord Lead 3s hoover-resistant, and they haven't been spontanously resetting since. The fix is quite easily implemented, very cheap – and at you own risk of course. THE FIX.
1. Open the NL3
2. Locate the PSU board, it's right side of the cabinet. Looks like this:
3. Locate the 3V voltage regulator
4. Mount a 2200 µF 10V electrolyte capacitor across the input side of the regulator. Solder the capacitor legs directly upon the legs of the regulator. Important to get the polarization right. The component is a mere 1€ / 1$. Doesn't need to be excactly those specs, similar or higher capacitance values should work ok, but it needs to handle at least 10V.
5. Close up and enjoy your improved Nord Lead 3.
// Henrik Munch & René Thalund, Denmark