I finally received my LimeSDR board yesterday. Sadly, I don’t think it is receiving power at all over USB, as nothing at all happens when being plugged in I’ve already fired an email off to Crowd Supply, but thought I’d post here with my troubles in case I’m missing anything completely obvious.
I have the board with the female micro-USB socket on it. I’ve used two different cables, one stolen from an external HDD I have, which spins up when using both cables.
No LEDs light up when plugging in to my laptop - which, for what it’s worth, successfully powered a LimeSDR board at the workshop I attended a few months ago - and nothing appears under Windows or Linux. I was eagerly watching the output of dmesg -w when inserting and removing the cable, with nothing being detected.
I saw in another post a suggestion for probing the VCC_EXT and VCC_INT pads with a multimeter - VCC_INT reads 0.3V and VCC_EXT reads 0.03V. I can see from the information presented here that VCC_INT is after the power source selector, so perhaps something is wrong with that?
I’ve not tried an external power supply, perhaps it’s something I should consider. Does anyone have any suggestions of things I could check over? A quick visual inspection didn’t show any obvious magic smoke leakage to any of the power stuff. One of the RF transformers with ‘GU’ written on the top looks a little wonky, but the wires are still attached, but I wouldn’t have thought anything on that side of the board would affect it so dramatically. Any help would be much appreciated
All these steps performed with the USB3 cable plugged in and powered:
FR38 (sheet 12, 2B) - located right next to USB socket as @Zack shows above.
Both sides of FR38 measure 5.14V.
First entry point of USB power, shows board connector is receiving USB power.
VCC5P0 USB also goes into FPF3042/IC25 (sheet 15, 2A) - located underside of board near power jack
Can’t see anywhere to measure the inputs and there aren’t any more components (that I can see) before the USB power goes in to measure.
Here’s a photo of this tiny little thing on the board. It looks a little wonky perhaps?
Output of this goes into FR57:
FR57 (sheet 15, 3A) - top of board near to power jack.
Both sides measure 0.32V.
Suggests to me that the problem lies somewhere in between 1 and 3, i.e. IC25. Perhaps it is not switching properly?
R48 (sheet 9, 7B) - next to IC25.
This connects to Vin_SEL of the switcher chip, and is at 0V. Sheet notes that if this is low then USB power is to be selected.
C375 (sheet 15, 2B) - next to IC25.
Noticed that this is connected to VCC5P0 USB. As expected, one side reads 5.14V. Just a point of interest as it is right next to IC25, possibly showing that the USB power is reaching it.
I have a similar problem as you. When I plug the cable into my computer LimeSDR doesn’t work at all. I have other LimeSDR that works under the same environment.