I have an university project, with 4 raspberry pi 3 (starter kit). I've successfully set 1 as an AP, and 2 with client (all 3 has mosquitto installed), they works fine. The AP is next to the router, in another room. So the clients and the router are in different room.
The problem is the 4th pi... It does not see ANY wifi network. So I thinked this is a hardver problem, because the other 2 sees 6 wifi networks, also my laptop and mobile sees too, both my wifi (with mostly 4/5) and the pi's (mostly 3/5 or 2/5) and some neighbor's wifi (mostly with 1/5 signal streinght). So I went back to the university, I said the problem, then I got another pi.
That's pi's wifi also had the same problem. But we upgraded the included power adapter, because that too doesn't worked - LOL. However I tought now, it's an OS problem, so I went down to the satellite wifi, I connected via UTP cable, I updated, I saw it sees next to the satellite the wifi, after update I went back and same, it can't see. OK, then, again back to university another replacement.
This started better, because the OS had fault before the INIT... GOOGLEING... ok, format card, copy fresh NOOBS... FAIL, card is read-only. Well, I wasn't able to remove the read-only (this session only read only), however I fount an 32Gb own microSD, format, copy, done. But this has the same problem again. Can't see the WIFIs... (however, sometimes at least it came up the router's wifi, not like at the previous ones.)
Then I tried inserted an installed OS from one of the working one, but it still can't see. It's hard to believe, from 6 cards, there's 3 defected ones and ALL IS NEW! Anybody, has idea what's the problem? Is this really hardware issue? Maybe anything to try as last hope?