I have a similar issue with my Helix 5, but here is a short story just in case it helps.
If it keeps happening I may find a way to ship to US for flat rate service, CDN repair is not be worth the cost.
On a good day, listen carefully, the unit will 'tick' when it powers on.
On a bad day, it will 'tick' and stay powered off.
I got frustrated enough to pull it apart (make sure you remove the microsd card when you pull it apart - they can get easily broken removing the logic board as they stick out past the housing)
carefully disassemble unit
thoroughly clean the board and contacts with electrical cleaner and wipe clean
I paid special attention to the buttons that always give up contaminants (this may be the main issue)
re-assemble
put on a good battery with 12+ volts
I have had to do this 3 or 4 times, and it has powered on after each as long as the battery is 'perfect' It can then keep running even when the voltage dips, but never seems to come to life unless a 'perfect' power source is used after cleaning.
This has made me think that there may be more to this than volts. Based on my experiences with the unit, I am tempted to put one of those cute little car boosters on the battery to kick start the unit as this last cleaning required a charger on my battery source for the first power on. then after that it has been starting up again.
I am not certain if it is
1. volts and/or amps
2. power off by circuit switch rather than unit power button (heard this can hang the CPU)
3. bad board (capacitor could possibly explain the thought that both high volts and good current are needed - have to check but I think the main cap is 35V)
4. dirty pads/rubber buttons that give up contaminants possibly making the unit think I am constantly pressing power for shutdown
or just my imagination.
either way, cleaning and ensuring the battery is in top charge generally wakes the unit up, but it seems it needs to be pampered with the entire spa treatment, not just one of the above.
Anyone with good electronics thoughts can let me know what they think and I will try it out, but I thought I would share my experience, maybe you can revive your unit too.
Just a note. I run a small lawn battery for the electronics on my tinny. Its a new battery that gets its full 12.6volts on a full charge. It runs a "Yakker" that is receiving TX from the Hellix 5 for GPS/depth to send to my iphone (works a treat on uncharted lakes)and a Pirahna4 finder at the bow.
These never have power issue. The Yakker does not get power from the Helix, I avoided this and only use the TX pin to the Yakker. I suppose it could have a potential difference, but the Helix when in the 'dead sleep' state will not power on even when directly connected to battery alone.
I have also disconnected power and held the power button to 'discharge' but that too alone does not seem to work.
Let me know your thoughts, maybe i can narrow it down well enough to help you too