[solved] RPi 4 unable to connect to WiFi

[guestxyz]

Used the official Raspi4 power supply. Should be enough: after unplugging it delivers power for about 15s.... and Raspi won't boot up during that time. Very nasty in view of missing reset button.

The WiFi problem looks like a bug. If I start with low resolution, the 2.4GHz network works nicely. If I go to 1920x1080 wlan0 either shows "not available" or so, or it shortly shows a neighboring network labeled with a red "5G", depending on what I click at the top of the screen, but my 2.4GHz network is not recognized. With my router set to 5GHz (+2.4) it works.

So, if there were a power problem, it must be within the Pi4B board (Copper traces too thin?).

[pica200]

That's strange. The only cause i can think of is noise from HDMI but the ports are far away from the WiFi + BT chip/antenna, the later is shielded and HDMI is probably not quite in the same frequency range. Maybe a RPi engineer has an explanation for this? I could not observe this behavior at all with full resolution.

[jaguay]

Hello everyone,

I just had the same problem when I disconnected manually from my wifi network and did not wanted to connect again.

Tried everything you guys wrote in this post, without success.

The solution was to change my SSID Name and password.

Sometimes the simplest solutions are the harder to find, because are so obvious

Cheers

Jorge

[mahjongg]

That's strange. The only cause i can think of is noise from HDMI but the ports are far away from the WiFi + BT chip/antenna, the later is shielded and HDMI is probably not quite in the same frequency range. Maybe a RPi engineer has an explanation for this? I could not observe this behavior at all with full resolution.

It could depend on how well the HDMI cable is shielded, the wires carry digital signals, which are square waves, meaning they have harmonic contents that go way beyond the frequency of the HDMI signals. If the HDMI shielding is weak or absent, the wires act like antennae, and could radiate a wide spectrum of frequencies.
in practice HDMI signals are already filtered, (using https://en.wikipedia.org/wiki/Low-volta ... _signaling) but the same principle applies, and good shielding is still essential.

[assadollahi]

I can confirm that changing screens will allow the WiFi to connect.
Pi4, 4GB, latest Buster (26 Sept 2019), powered via USB-C battery bank, 3A
Side note: Same battery bank has 3A USB output as well as 3A USB-C output,
the pi4 only works in a stable manner when connected via USB-C to USB-C.
Strange, hm? Back to screen vs Wifi:

1) small screen 1: 1920x1200, big screen 2: 2560x1440, Wifi doesn't connect
2) remove screen 2, reboot: Wifi connects!
3) re-connect screen 2, but set resolution also to 1920x1200, reboot: Wifi works!
4) removed small screen 1 and put screen 2 in 1920x1200 resolution: Wifi works!
5) puttin screen 2 into 2560x1440: Wifi doesn't work anymore!

Could it be that higher resolutions have higher demand in power and thus Wifi is underpowered?
However: When powering from battery via USB-C, at no time I get the lightning bolt. So it shouldn't
be a power issue?

[bjtheone]

Sounds suspiciously like an radiated interference issue. I would try buying an good, very well shielded HDMI cable for the higher res monitor and see if that changes the behaviour. Given there is not a flood of complaints about issues with high res monitors, I highly doubt the issue is in the shielding and traces on the PCB (thought you could have a defective one).

Another interesting test would be to see what happens if you only have monitor 2 connected, running at the higher resolution. If that still has issues, I would definitely try a better cable.

[Shadow_7]

I've had issues where turning on an LCD display near the TV or LED lights would interfere with ATSC signal reception (OTA TV). On an older HDTV (circa 2006). You might fool around with some tin foil to shield things. Assuming the wifi is not near the TV/Display. I originally got my mom to switch to linux for a bit because windows wifi would forget it had a wifi device if the signal dropped below 34% strength. A tin foil covered pizza box on the opposite side of the desktop helped improve the signal strength (but didn't improve windows). A couple zip lock bags, electrical tape and wrapping odd coax joiner/splitter/extension points with tin foil too for the TV. But country life some 40+ miles from the big cities. You might also change your wifi channel. Older cordless phones would interfere with channel 11, and all your neighbors probably went with the factory default channel 1. So try channel 6. Just a thought. Newer LED lights seem to interfere less with things, but are still more problematic to wireless things than incandescent bulbs were. Try turning off the lights and see if wifi works again. A strange world we live in these days.

[netikras]

I doubt it's HDMI cable.

I had some doubts at first hence bought other 2 RPI4s believing the prior one(s) to be defective. So here's what happened.

At work I have a need to monitor multiple charts at once LIVE. So we bought a 4K display and a rpi4 to drive the dashboard. Popped in a copy of the latest Raspbian Buster and fired it all up.

At first all was nice and dandy, 2 or 3 days later the magic started to happen.

Out of the blue network all the configuration disappeared and I no longer could bring the network up (P.S. I was using WIFI connection and a BT keyboard). Every time I tried to connect to any WIFI AP I got the same weird IP address that did not conform to either of the networks. Routing table was empty, adding routes manually did not bring the network up. Tried multiple restarts as well. In the end decided to reflash the image and start all over again. That's the first thing that was weird and not sure whether in any way relevant to your topic, but.. maybe?

The new image was also working perfectly for a few days. After that something new started to happen - at some mornings when I came in to the office I used to find the RPi4 disconnected from WIFI. Reconnecting back to the network did work most of the times - the other times I had to restart the device (sudo shutdown -r now). That happened a few times. Still connected to the same 4K display.

Later on something new started happening: the BT keyboard could no longer connect to the RPi. Multiple attempts to rfkill the bluetooth device did not help (or maybe did, just not enough?) - the keyboard still was not able to connect, although sometimes I could see the cursor move a few milimeters (the keyboard has a trackpoint). Restarting the RPi "fixed" the bluetooth thing every time.

We got another RPi hoping that one was defective. The new one had the same issues too. I brought the old one home hoping to do some tests and identify whether it is OS or HW issue. I hooked up the serial connectors and connected to RPi with my laptop. No display connected (I do not have HDMI displays). I set up WIFI connection to my router and connected via ssh for more convenient access. After a while I walked away to have lunch and came back to find a frozen ssh connection. Hooked up UART adapter again to find that WIFI got disconnected, wlan0 got the same weird IP address and an empty routing table. Could not reconnect to my wifi router without a restart. Let me repeat myself: NO display was connected to the RPi. Before restart I saw some errors (bcm? Something I translated into Broadcom at that moment) with an error code -5<something> (-52? -53? Can't remember). Restarted the device and the network came back up. Could not reproduce that error ever since. But I saw it at the RPi in the office a few days later (w/ 4K display), when BT failed again.

[not in chronological order] another weird issue was happening with all the RPis and that was the reason why I bought the 2nd RPI4. As I was setting up the first RPI4 I did not yet have the 4k display, so I was using my 1920x1080 monitor. All the set-up process went fine, then we got the 4k display. Plugging the rpi4 to the display was troublesome - it could not stretch out the image to 4k. Reflashed the sd card and rebuilt the dashboard on the 4k display this time. All went peachy. Then plugged in my monitor (can't remember the reason why tho) and all I could see was black. Not even the RPI logo was seen when booting up. Nothing. Only black. But the OS booted up as I saw new records in syslog later on. Tried messing with boot parameters in boot.conf (?) - didn't help. Since then even 4k randomly does not work. Reflashing the sd card again did fix it. Apparently RPi4 (or Raspbian Buster?) does not like to be switched between different resolutions, if either of those resolutions is 4k. If I set RPI4 up using 4k only - it works well and is stable (image-wise). If I try to connect it to any other display - video stops working randomly on any displays you are to connect the RPi to from that moment on, until you reinstall the OS. But that was the point when I ruled my first RPi defective. That was a wrong move as other 2 RPI4s I got (all from different vendors) had all the same issues



Not sure whether my story has any value in this context. Maybe it could suggest it's not the HDMI cable to blame network issues. Maybe it has something to do with internals of the board as I got network outage even w/o any video cables connected. Maybeit has something to do with on-board graphics, as they are obviously misbehaving. And maybe it's just an OS issue since after reinstalling the OS things get back to normal. What's still bothering me is that I still have the first RPI4 at home connected and booted up waiting for network to go down again to have a proper post-mortem analysis. Could not make it happen - it's been a few weeks now.

[pica200]

Maybe this should be moved to a new thread. This sounds to me like the driver for the WiFi and Bluetooth combi is going nuts or the firmware of it. Edge case with non-standard conform router?

[jamesh]

I think this is the same as this

https://www.raspberrypi.org/forums/view ... 0&start=25

There's a test firmware out - sudo rpi-update will get it - can you see if it helps?

[mohit1]

Having same problem

What i observed is once wifi connects
then doing 2 reboots
It wont auto connect to wifi

Also you need to powercycle 2-5 times to get it connected to wifi once