Intermittent power up - Carbon GT - FIXED

Hi guys, old skater and understand electronics and speed controllers etc (background is electronics) but new to electric skateboards and don't have circuit diagrams to work with.

Was gifted an evolve Carbon GT and it cleaned up really well. Was all working fine but batteries were failing and could only ride for a km or so on level ground (slowly), not up the slightest of hills and only at Eco mode, battery still ran down fast. The last charge I did on the old batteries it wouldn't turn on for a while and couldn't find anything wrong. Put it all back together and it worked fine and couldn't fault it so thought no more about it (this was after about half a dozen rides on the failing batteries).

New 10s5p Marsen batteries arrived and installed a day later and work great, but the power issue remained and now mostly won't turn on. Looking at the BMS negative in and out wires, when power switch is off they have 38.5v across them (batt at 41.4). Switch on and it slowly drops to about 38.1 then climbs to 38.9 then slowly drops again (slowly as in about 5 seconds). Cycle repeats for ages. Then all of a sudden it quickly drops to 0v and the board powered up. Then without turning off, reinstalled the deck and went for a 10km ride, working my way up to GT mode up hills etc and no issue (first ride with new batteries and first real ride on a e-board). Returned home and turned it off and power light won't turn on again. I did notice yesterday during my last testing at one stage the power light on the board was off but the remote was connected and it was locked in Safe mode. Motors worked, but switched board off/on and never came back up. Have tried disconnecting battery for an hour, no change. BMS is the later heatsink version and was new/old stock and only just fitted (had not yet been installed when I was given the board).

Anyone have experience fault finding the Evolve electronics without replacement parts to throw at it? Or anyone have any circuit or wiring diagrams available? I will try to have a deeper dig into it over the coming days, but basically seeing if I can short cut the process from anyones previous experience.

Edit - just went out to have another look, stil the same, charged it last night and that worked OK but wouldnt turn on, tried charging just now and no power going into battery either through BMS (showing 38.9v across BMS neg in./out). Unplugged battery for 10 seconds and plugged back in and it worked, turned it on/off a dozen times and now cant make it NOT work.. sheesh. Suspecting possibly a capacitor drying out, will have to strip it out and have good close look (tried thumping, twisting moving and a 10km ride and none of that makes any difference so I dont believe its a bad connection).

 

Update to my power issue. Pulled it all apart again to install the drop spacer for the electronics as I have installed a 10s5p battery pack. So whilst out had a good look through it all. Power switch working perfectly, right through to the switch input on the BMS. Pulled the heatsink off the BMS and noticed some mild corrosion on the board at the 11 wire socket so cleaned that up. Also noticed horrid glue on the board holding the wiring, have had bad experience with that over the years of my electronics repair life, especially around heat. Removed all the glue, removed the wires and resoldered them. One was the serial connection to the main board, the other power and the thermistor. When in removed the glue from the thermistor cables one wire was actually broken (I think corroded). Repaired all wiring, cleaned all corrosion and rebuilt it all and seems to be working so far.

Though did have issues with occasionally not wanting to move though all still powered up. Recalibrated the remote and set the brake minimum with the button pushed a millimetre or so as I think it was thinking brake on so no power and was stuck not exiting slow mode...

Will see how this goes.

UPDATE. 3 rides, 10km, 17.5km and 19.5km later and hasn't missed a beat. Not sure whether it was the corrosion, the possible broken wire to the Thermistor or the degraded brown glue, but bo issues at all since.