No power for a new LimeSDR

Hi all,

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 :frowning: 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 :slight_smile:

Hello @Jagmills,

Could you measure the voltage on FR38 component (both sides), please. It is highlighted in red in the picture bellow.

Hi @Zack, thanks very much for replying. I get 5.14V on either side of FR38.

So I had an evening to sit down with a print out of the schematics :slight_smile:

All these steps performed with the USB3 cable plugged in and powered:

  1. 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.

  2. 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:

  1. 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?

  2. 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.

  3. 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.

Hello @Jagmills,

As far as I understand, you already contacted CS. Ask for a replacement, please.

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.