Posting this in case it's of help to someone else.
I bought this Roku unit a couple of years ago. Been working perfectly until yesterday then, suddenly, the remote no longer worked. The Express 4K comes with the simple remote, not the voice one. I could use the app to control the unit so viewing was not a problem but a pain not having the remote.
Investigation (looking at the transmitter with my phone camera) showed the remote was not transmitting the infrared (IR) pulses it should be. Getting into the remote was fiddly but managed to do this without significant damage to the remote body. A quick probe with my oscilloscope showed the signal was getting to the LED but not light coming out. I had a spare IR LED in my bits box, and 10 minutes later, I'd replaced the failing part and the remote was up and running again.
