I love these little Planet Waves SOS tuners. They call them SOS: Strobe On String and they work by pulsing two little LEDs at a particular frequency. You pluck a string and shine the light on it. If it’s out of tune, the pattern made by the light wobbles about. When the string is in tune, the pattern becomes stable. Easy peasy.

I’ve got a couple of these in my workshop as I frequently need to tune guitars (or even necks mounted on temporary—surrogate—bodies for refrets) with no pickups to plug into an external tuner. The workshop can be a noisy place with extractors, dehumidifiers and music so it’s easier to use one of these SOS tuners than it is to turn off the noisy things to allow me to hear the correct tuning.

Seriously, they’re great. Everyone should have one. Off you go to Amazon and get yourself one: Planet Waves S.O.S. Guitar Tuner

That said, sometimes, one of the LEDs stops working.

Single LED not working in SOS Tuner

I found this a couple of times and it was annoying. It’s not possible to use it with only one LED working and, after this happened to the second tuner, I cursed Planet Waves and assumed some sort of manufacturing defect. I even threw out my first tuner because only one little red light remained.

Turns out, I was an idiot.

If you’ve got a Planet Waves SOS tuner and one of the LED’s fails, don’t chuck it in the bin. Instead, replace the battery. Presto! All back to normal.

It seems a bit of an odd system to have a single LED fail while the other one works as the battery is drained but that’s what happens. If one LED remains working as brightly as normal, a battery isn’t the first thing to leap to mind. That’s what it is however. In my case at least, but this has worked for me on a half-dozen occasions now.

Incidentally, these use those little coin-cell battery things. Buy them from eBay if you need them. You can usually get them in tens, shipped from Hong Kong, for the same price (or less) than you can buy one for in your local shop. I’ve got about ten year’s supply of them for a few bucks.

Oh, and there’s a bass version of the SOS tuner too. Planet Waves S.O.S. Bass Tuner