Aha, that power/connection sequence works. Thank you! 
I found that it also works when the SL is powered up and connected first, and then the axo is powered up.
These sequences might indicate that it's not the power source as such that's the issue (axo runs fine when powering the SL over its USB host port), but rather that the SL has to be initialized before the USB connection is made.
I confirm this procedure works also on the Remote 25 LE.
Axoloti powered from USB, Remote 25 LE powered with 9 AA Batteries, switch set to DC power/Battery. The sequence is fundamental, otherwise it does not work.
My Remote 25LE died accidentally (ehm water + big fall).
But fortunately ebay is great and I got a 12 years old Remote 25SL (mk1) for 40GBP. It works fantastically with the Axoloti following the procedure above. It is nice to have many parameters on the display. Great old controller indeed, probably one of the best for the Axoloti?
I bought a used Novation Zero SL MK2 recently and came to this thread because it was showing the same symptoms.
Using an external PSU fixes the issue indeed, thanks!
Hi, Just a question about Novation Zero Sl MK2. Does it possible to control the leds via Axoloti? I can do it with a Nanokontrol 2 and does it allow to use it as a sequencer, for example. I´m thinking in trying with a novation remote zero.
Also I wanted to ask u if you thinhk there is enough space inside this controller to put the axoloti board inside.
Thanks in advance!
You can control the LEDs via midi when the Ableton preset is selected.
That is the simple avenue. Additionally, there is a sysex-way of controlling the Zero which is needed if you want to control text-display. When I tried that sysex mode, I noticed that I lose that "touch-sense" feature which updates the text-content after you touched a different group of controls.
I have not opened it up and I did not intend to, so I don't know whether the axoloti would fit. It's actually a neat idea, I think only that I would be too lazy to try myself.
Thanks a lot! I will post my sequencer proyect soon on this forum, so you could see what I´m trying.
This URL is from another forum. I think that document is also available somewhere on focusrite/novation's site.
It describes how to write your own "Automap" mode. It would require receiving and responding to sysex coming from the unit however, so some things cannot be achieved when using the Axoliti with the current firmware.
Still, being able to display custom text on the display seems potentially useful and it does work for me.
The third, hidden port is not visible to the Axoloti.
Very curious to hear your progress on this as I have both a Remote SL 61 and a Remote SL zero and would love to be able to control at least the Leds/buttons or at most update the screen with the axoloti. have just downloaded your sysex objects and will have a look, is your help patch just designed to put the remote sl into Ableton automap mode?
Unfortunately no progress was made due to work and focus.
I do plan to change the code drastically, it only reflects my state of exploration then.
I do not remember clearly, if I left code specific to the Zero SL in the help patch then it might be a mistake.
You don't need any sysex for controlling the Button LED's when using the Ableton mode.
I'll have to have a look at how to do that. Thanks for letting me know it's possible.
Is it by use of CC then, and can the screen be updated that way too, anything at all would be great