The screen on my guitar tuner (Snark Super Tight Hz) went dark yesterday. At first, I thought that the battery might be flat, but then I noticed that the screen
was working, it was just very dark. I used my head torch to illuminate it, and yes - the tuner still worked. Still, I didn't fancy having to don the headtorch every time that I wanted to use the tuner!
I thought that there might be a fault with the screen's backlight. I consulted Google, and sure enough, people were talking about the same problem. Apparently, some of the devices have poorly soldered backlight connections. I followed the instructions, dismantled the device, and resoldered the connections, reassembled everything, put the battery back in, switched the device on and...
... the screen was
still dark!
Back to Google... Other people suggested that the problem might actually be due to an almost flat battery which had enough juice left to power the tuning circuitry, but not the backlight. It sounded unlikely, but just maybe...
I had an emergency front bike light which I remembered used 3032 cells. I checked that the light worked - it did - so I took one of its batteries out, put it in the tuner, switched it on, and... the tuning worked, but the screen was
still dark!
I had a think about it... If the device struggles with semi-flat batteries then substituting a potentially semi-flat battery for another semi-flat battery proved nothing!
I needed a
new battery... I ordered a pack of 10 last night and Amazon Prime delivered them this afternoon. I put one of the new batteries in, switched the device on, and the screen...
...
LIT UP!!! 
So, yes - a Snark tuner backlight needs to be fed from a battery with a decent amount of charge left in it!
