Fix for UAEFI sometimes not starting without USB connecteed

[gurov]

image.png

from discussion on discord:


5vp does not light up with just 12v below a certain battery voltage, causing a no-start condition

this was traced down to a severe enough drop at the main 5v regulator that would cause the main MCU to power down, aborting enabling 5vp, entering a loop.

fix is rather crude, but it's to force 5vp to initialize forcefully, MCU or not.

10k resistor between pin 7 and 5v rail, like in the picture.

[AndreyB]

this was traced down to a severe enough drop at the main 5v regulator that would cause the main MCU to power down, aborting enabling 5vp, entering a loop.

We still do not know real root cause right?

Similar looking boards one would work another would not, right? https://github.com/rusefi/uaefi/issues/59

[gurov]

correct, still don't know the actual root cause, just breadcrumbs of symptoms with comparison to good board

[yingste]

Not to necro an old thread but this might still be the case. Have a UAEFI hooked up to a bench power supply putting out 12v with nothing connected besided power and ground and it appears the 5v rail isn't firing up. When I plug in the usb to a laptop the 5v rail stays up even when removed. I don't have a variable power supply but it looks like even as low as 12.2 and I don't see it kick on. Can be a bit inconsistent though. I have had a case where I know the battery was low and the 5v line fired up fine, enough to bump start and get the generator spinning but not enough to use the starter.

[AndreyB]

See also https://github.com/rusefi/uaefi/issues/85

[MauroSignoroni]

Anche la mia uaEFI personalizzata aveva il problema discusso in questo post

a24d22fe-aad6-403a-b411-046ae87883b0.png

Per risolvere il problema ho eliminato R141 e aggiunto R142 nel modulo mega-mcu-100

R141 R142 mega-mcu-100.png

con questa modifica funziona perfettamente.

non sò se è la soluzione corretta, non ne ho trovate altre.