BLUF: I have what I think is a dead BM818-A1 modem. Is there any way that I can try to repair it?
The long story (in case it happens to someone else): I left my phone on the charger for a while, but when I came back to it the power was off even though I left it on. I tried turning it back on and got to enter my encryption password and continue the boot (I got a successful password message). However, it almost immediately rebooted and I was prompted again. I did this a couple times in vain.
I went through the Jumpdrive Procedure on my Fedora system and all the filesystems on the phone were fine. There was enough free space on /boot, which is a common cause of this issue that I found on the forums here. I ran e2fsck just in case but that didn’t find any issues. However to my surprise, after I booted the phone again following this procedure it did so successfully!
I thought it was maybe a dirty unmounted partition and thought nothing of it. However, one of the steps for getting to Jumpdrive is to turn all the HKS to their disable position, thus killing the power to the devices they control. After I got into my phone following its successful boot, I enabled the devices again with the HKS toggle. When I did so for the modem, the phone immediately crashed to a black powered off state, ready to boot-loop again.
Luckily I have another BM818 modem, but it’s the E1 variant. I live in the US so although it works, I’m worried my coverage will suffer. Better than nothing though and at least my phone works again after installing it.
Now, since the Purism Store has no stock of BM818-A1 modems, is there some chance I can figure out what’s wrong with mine and repair it?
Even a dead modem shouldn’t be able to crash the phone. I think I would want to rule out a software issue before “repairing” the modem.
I guess it depends on how functional your phone currently is v. how much disruption you are prepared to tolerate in investigating the current situation.
If nothing else, do journal messages give any indication of whether the phone is recognising the modem when the modem is switched on and/or show any related events?
Have you contacted Purism about the out-of-stock? Yes, the shop shows the -A1 variant as out-of-stock but …
Any chance that you can source the modem somewhere else?
As Purism is investigating other modem options, maybe they can supply you something other than a Broadmobi, albeit that that would make you an enforced early adopter.
By a software issue, do you mean software on the modem? I was able to get back to a functioning phone with a replacement modem so I think the problem is probably localized to either the software or hardware of the BM818-A1. That said, I don’t mind a few nights of tinkering with it. One of the things that makes it difficult to diagnose while installed in the phone is that when I energize the modem by turning the HKS back on the phone immediately powers off and reboots. It’s instant so I don’t think it would even have time to write a core dump.
I did try to find another BM818-A1 from elsewhere on the web but no luck. I haven’t tried contacting Purism yet but that’s not a bad idea. As far as alternatives, I think the most promising would be from another thread here recommending the Sim8202G from the 5G is here thread here on the forums. However, I’m a little hesitant given the cost and lack of integration maturity with PureOS. Albeit, there are workarounds and ways to get it functioning, but it looks like it isn’t quite as stable as I’d like for a communications device in potentially emergency situations.
No, I meant software (or settings) on the phone itself.
So, let’s say that you aren’t using the µSD card reader for anything else … create a bootable µSD card on a host computer, shut down phone, install µSD card, boot from µSD card … see whether problems still happens.
Not sure what makes you say so, of course a faulty modem can do that. Based on the symptoms it seems pretty clear that the modem is causing power brownouts, possibly due to an electrical short that may have developed there.
Why do you think that? A “dead modem” could absolutely cause a power management problem and result in a full shutdown or crash. The fact that they don’t have this issue with a different cellular modem seems to point to that. There have been examples of modem pieces breaking and causing possible shorting Librem 5 loses its modem - #10 by Dlonk . I should point out that not all “shorting” is the same and that it could result in dysfunction (modem doesn’t turn on) or destruction (magic smoke) — the phone having an immediate shutdown based on powering a specific modem would be one where I would worry about damaging the phone’s power circuits and, personally, I wouldn’t encourage playing around with that modem other than maybe investigating whether it was seated correctly.
Indeed, this other topic describes exactly what happened to my modem: the metal shield / cover became detached. After reading the other comments here and in the other thread you linked, I am sure that it is some kind of short due to the loose metal cover contacting some of the circuitry on the modem board. I probably should have noted this detail in my original post.
I wonder if it’s something I can repair. Someone mentioned it may be able to be soldered so I suppose I could take a good look at it and give that a shot. Or, I could just wait until (hopefully) Purism gets the BM818-A1 modem back in stock and get a new one, just keeping the E1 modem in place and dealing with the spotty cell coverage.