I’d say the weirdest thing in this fault is the battery voltage… do you have a BMS hooked up in the discharge path or bypassed? Dipping from 42V to 21V is pretty extreme, seems like the battery is becoming disconnected somehow.
@Deodand
Some strange % voltage sag happened during last ride (but the actual voltage graph looks ok to me)
No throttle for about 0.5-1 sec
Happened only once since 2.500km on that board but twice during that ride (the second one without that strange “no throttle” issue)
Any ideas? Thank you in advance 
Upload the actual metr data please not screenshots please.
Some sag is to be expected. Keep in mind the actual ESC is sampling at 10 kHz while this plot is only at like 20 Hz, so it is very possible to miss data in the graph that will be reported on the fault data. Impossible to tell why you would experience a cutout without the data from the ride where is happened.
Goddamn. I didn’t notice that. The voltage drop doesn’t show up at all on the Metr trace so it must’ve been very fleeting. I see that the Metr voltage measure is smoothed but a fluctuation of that size is too rough to be smoothed.
Yes, there is a BMS in the discharge path. I wonder why it would cut out there though. It wasn’t a high draw or anything. I was on smooth terrain so it’s probably not vibration-related. Hmm… the plot thickens.
Thanks for the insight, @Deodand. Really appreciate the pointer.
I’d recommend bypassing the bms for discharge and seeing if you get any future cutouts.
1 Like
So after a full overhaul and a few hard test runs around here, I drive out to some cool trails about an hour from me and this happens:
Battery voltage drops off a cliff. Duty cycle hits 114%(!?). Lights are on but nothing’s happening. I wasn’t pushing it hard at all. Wasn’t hitting crazy rough terrain. Metr tells me I’ve got about 7v coming in. BMS app tells me I’ve got 50v going out.
Anyway, I drag the thing back to the car. Drive back home and strip it down to see what’s up. Everything looks intact. No soot. No exploded components. Everything looks mint. I can measure 50v coming in on the main power lines at the PCB. I checked the momentary switch just in case but it’s fine. The second fucking Unity within a few small km’s is ded.
Notice also at 13:13:14.015 there’s a voltage blip there as well.
I’m guessing that this isn’t symptomatic of the usual anti-spark death issue.
Paging @Deodand, @Fatglottis, @seaborder: Is there anything I can do to further troubleshoot this?
I swear to God, I’m losing faith in this shit.
1 Like
This looks like a loss of battery voltage.
Are you discharging through the BMS?
Do you have photos of your battery insides?
Check for broken battery series connections.
Do you have an XT90 that’s vibrated apart? Are they all tied with twine or cable ties so they cannot disconnect?
1 Like
I can do all of this but the fact remains: 48v is reaching the Unity PCB but it’s not turning on. It was reporting 7v when it was seen to be getting 48v.
2 Likes
what was reporting 7v? the unity pcb which was not on?
by unity pcb do you mean the unity itself? or those sentinel/007/unity pcbs found in lacroix boards?
2 Likes
Yes, this; good question. If the motors are spinning, they can power up the ESC.
I guess I assumed you were talking about on the bench…
1 Like
sounds like the usual anti spark issue or similar, also there was a drv fault triggerd in the logging. That does not mean there is a DRV Problem for sure. After fixing the Power issue I would check the drv/powerstage area and try if you can trigger the issue on the bench again
1 Like
They are connected to a momentary switch. I’ve tested the MOM pins for continuity and it’s functioning correctly.
Fair point. Metr was reporting 7v (while the Unity was still on). When I checked the BMS app, it reported ~50v. I concede that when I had the opportunity to physically measure voltages across the system, there was nothing that was reporting 7v. I’m not skilled/knowledgable enough to take measurements on the Unity PCB beyond the PCB’s main power terminals.
Yes, the Unity itself, measured here:
Granted. Your assumption was correct: the board was frustratingly stationary.
If by ‘power issue’ you’re referring to the likelihood of a disconnection along the power supply, I honestly think that we can rule that out. I checked and double-checked after @Deodand’s earlier observation and I did so again yesterday. Solder joints are solid. XT90’s are so tight I need tools to unplug them. I can accept that the BMS is a potential point of failure here but my gut tells me that the issue is with the Unity.
Could you share a few pointers on how I can, “check the drv/powerstage area” please, @seaborder?
I’ve had other feedback by DM, saying, “It sounds like only the precharge circuit is broken”, as well. Can it be coincidence that I’ve blown two Unity’s a/s systems? I mean, could I have fucked up some aspect of the build or configuration that makes this more likely to happen? What factors determine a/s health (assuming it leaves the factory healthy)?
Thanks everybody for working with me on this. I really appreciate the support. You guys rock 
1 Like
It is difficult to see… is this blown? It’s the charge pump for the transistors doing the precharge.
I guess you have zero volts across the big capacitors when you try to power up?..and that would be why its dead stationary but alive when being powered backwards during regeneration from the motors.
1 Like
Hey guys, I have been trying my best looking through the forum for solutions to my focbox unity but eventually gave up and bought another one. This is ultimately my third purchase of the unity. Anyways the issue always happened when one of the pins on my vx1 receiver would short out I am not entirely sure which pins specifically, but when I try to turn on the unity it powers off in seconds. I saw that this could be a bootloader problem that would just require a reflash with a St-Link v2, but that has been no luck either (I tried finding the reset pin, and double-checked the wiring on the St-link’s pcb and orientation of the jumper cables on the unity. I checked with my multimeter and the unity only supplies power to 5v and not 3.3v does that mean the MCU is messed up permanently? This is my third time shorting something out with the vx1 receiver and I wish there was a protection circuit to prevent this from messing up my unity.
No, I don’t think so. Everything looks kosher. The application of the conformal coating is definitely questionable but nothing looks blown.
…and zero volts across the caps, yes. To be clear, the unit is totally unresponsive if I try to power it up.
7 Likes
Your picture still does not convince me… it still looks like a hole… coating burnt off 
You might be right. Its just that the unities I have reworked have had a hole in that component on that same place
Perhaps scraping the coating off will reveal the dirty truth?
7 Likes
Well I’ll be damned.
You’ve got a hawkeye there, @Fatglottis.
What’s the fix? Replace it or rip out the a/s?
And guys, I really need to know: is this just a recurring product issue or am I over-driving it somehow and causing this to happen?
7 Likes