Hi
I had a couple of dead nRF9151 devkit boards that were probably accidentally overvolted and wanted to see if I could fix them rather than throwing them away. I bought a couple of new nRF9151 chips and a handful of the surrounding components and learned how to do rework. My initial attempts failed, soldering 0201 components without a microscope is extremely difficult and reflowing a 113-lead QFN without a stencil is also apparently quite tricky. I shorted VDD_NREF at one point and blew a ferrite near the USB connector so had to replace that. I am making progress though, yesterday I managed to reflow the chip without bridging any of the GPIOs, I thought everything looked good, it powered on, was recognised and flashing works again. Had a brief moment of elation at having made it work but then realised the modem wouldn't initialise:
[01\\'00:02:31.011,657] <err> nrf_modem: Modem library initialization failed, err -116
[00:02:31.019,836] <err> nrf_modem: Modem library did not initialize: -116
[00:02:31.027,465] <err> modem_antenna: Modem library did not initialize: -116
[00:02:31.035,491] <err> lte_lc: Modem library init error: -116, lte_lc not initialized
[00:02:31.044,250] <err> modem: nrf_modem_lib_init: -116
[00:02:31.050,292] <err> main: modem init failed
I tried flashing the latest modem firmware and although it succeeded it still doesn't work. I've now discovered the LTE pin is shorted to ground so it wouldn't work anyway but I don't think that would manifest as the modem failing to initialise.
My current working theories are:
- bad joint / ground somewhere under the SIP
- issue with the modem supply rail, although all my power rails read clean when it's one. possibly an issue with decoupling parts although i can't see any at the moment
- SIP death due to the repeated heat cycles i've put it through
Is there anything else that might cause the modem to fail to initialise like this? When replacing the decoupling parts I tried to use the same parts as the original schematic but its possible I might have made some mistakes. Maybe one or two caps are slightly out of spec, I don't know if that would cause the modem to fail to initialise though.
This has been a really fun learning experience and seeing the board power up and boot again after being completely dead was an awesome feeling :)
Cheers,
Mark
