I have 3 Raspberries set up in cases with holes in them. Each Raspberry has a microcontroller and a wireless adapter attached via USB. Two Raspberries have been working fine for 5 months now. However, one setup fails constantly.
I replaced the faulty raspberry with a new one because I didn't have the time to check why it was failing. It just didn't boot, only the red LED was active.
I thought it could be the fuse and just replaced it with a new one. After a few days I got the faulty one booting again, after flashing a new image to the SD card. This didn't last long, though. After a few minutes, I couldn't reboot anymore, same situation - red LED only.
Today, the setup failed with the new Raspberry after 20 days and I think it's the same error. The Raspberries get quite warm - about 55°C, maybe a little more. The wireless adapter seems to produce a lot of heat as well.
Besides that, all setups use the same hardware - because of that, I don't think that its the SD-Card model or any other component.
Why is this setup failing multiple times while the other setups run perfectly?
What do I have to check in order to identify the source of the problem?
Any ideas are highly appreciated.
EDIT: I have to add that all those Raspberries are never shut down. They run like 20 hours until they literally get powered off, until they get powered on again after about 7 hours.