I've recently updated three Archer C2600 devices to OpenWRT 23.05.5. I then noticed that one of the devices shows only one of the two Wi-Fi interfaces in /etc/config/wireless. I checked my logs and I'm quite sure that this was already the case before the update.
I then checked lspci and on the working devices I get this:
On the 'broken' one, the 0000:01:00.0 Network controller entry is missing. I also checked dmesg, but I didn't see any obvious issue.
I bought the routers used, so I wonder if it's possible that it's just been misconfigured (e.g. wrong region) and whether this could have such effects. Or maybe it's just broken? Are these chips physically separate cards, so would it be useful to open the device and check mechanical connections?
Not necessarily 'massive' (in the sense of obviously visible damage, like burned parts, cracks, ripped components of traces), one aging component (capacitor, mosfet, etc.) might be enough.
While unlikely, it happened to me once that the 5GHz radio in my TP-Link Archer C7v2 stopped working. It wouldn't show up in dmesg anymore. Luckily, the 5GHz radio in the Archer C7v2 is not part of the board itself, but a replaceable miniPCIe module. And indeed, replacing the 5GHz Wi-Fi module solved the issue.
Now, a word of caution: If I recall correctly, I also tried flashing the stock firmware before replacing the mini PCIe module and that wouldn't boot anymore, so I had to resort to the TFTP recovery method in order to reflash OpenWrt and regain access to the device. So, if you flash the stock firmware, be prepared that you might need to recover the device if your 5GHz is really broken.
While the wireless is technically PCIe based on these devices, the components are part of the main PCB and not replaceable. Economically doing so wouldn't really be viable either (a filogic 820 device would start roughly in the same price range as a usable PCIe card, which you can't insert into this PCB anyways), technically there are more difficulties (even for your use case), be it 'just' the preinstalled drivers/ firmware or more importantly the radio calibration data (ART) and MAC addresses, which are usually not part of the PCIe card on these devices, but put into the main system flash (changing the card, even if it has its own EEPROM, as a good consumer card does, would clobber this with the now-incorrent data from the system flash). Replaceable WLAN cards in APs and routers have become rare, mostly only found in enterprise hardware (and even there not regularly).
tl;dr: if a WLAN card of a modern router is broken (and not easily/ obviously fixable, it rarely is), you can only replace the whole router (or live with the new limitations). Filogic 820 starts around 30 EUR, ipq807x around 70 EUR and filogic 830 around 140 EUR - depending on your location, there might also be good alternatives that may be be even cheaper - and the various used markets are also worth checking,
Thanks for the tips and insights @slh and @silentcreek. I flashed the otiginal firmware using the tftp method. According to the web Interface, everything worked normally. However, turning on the 2Ghz Wi-Fi had no effect whereas turning on the 5Ghz Wi-Fi activated the 2Ghz LED. In either case I however didn't see any WiFi SSID at all.
Out of curiosity, I opened the device. I was quite surprised how clean and integrated everything is, it's been a long time since I looked at a consumer router PCB. As you predicted, I didn't see any obvious faulty components. However, it looks like the device had some liquid accident with its previous owner, there was some liquid residue.
Anyway, I guess the device is just broken. I wanted to upgrade to some tri-band device for proper meshing anyway, so it's probably time to replace this device Thanks for the suggestions
