#1
Right, it's the peg which is attached to the G-string.

Ill be playing, and I'll notice that I sound out of tune. Whats happened is, the g-string has de-tuned.
I tune it back up and continue, and go out of tune again, except this time the string pitch has got higher.
Also, when I'm tuning said string, all the other machine heads tune up incrementally depending on how far I turn them.
On the one in question, I'll turn it slowly and nothing will happen. I'll turn it abit more, and the string pitch will suddenly rise or fall.
So its possessed of something.
Is this definately the tuner, or could it be something else?
Its not the string because I've recently changed them and it still happenes.
#2
it could be the way you wrapped the strings around the peg, or it could be the fact they have stretched out yet
#3
It could be how you have the thing strung and the string is what is slipping.Another possibility is the string being pinched in the nut slot.Also,make sure you tun the string down then UP to pitch if you go too far then detune and go back up to pitch. The chances of a actual tuner going bad are there but,very slim.

Bhaok

The following statement is true. The proceeding statement is false.
#4
It could be, but to be honest I doubt it. From a mechanical standpoint the worm gears in machine heads are pretty idiot proof, unless it's seriously rooted I think it's more likely to be a problem with your nut pinching the string or perhaps the string actually slipping around the post. Try making sure your string has 4-5 complete turns around the post when re-stringing and try using a soft lead pencil to put some graphite into g-string slot in your guitar's nut. You could also try enlarging said slot a little but it's a tricky job without a nut file of the right size, so unless you know what you're doing it might be a job for your local guitar tech. If none of that works then sadly it might indeed be new machine head time.
Hope that helps
#5
Thanks guys this helps.
I think it will be the way ive put the strings on because they arent wrapped around the peg very much.
And now that I think about it theres what, 2 gears in the machine head? Yea that wont go wrong very much.
Next time I restring Ill do it properly lol.
#6
check the nut that holds the machine head to the guitar is tight.

it might also be you haven`t stretched the the string sufficiently, and the relationship between th D and G, wound to unwound,check your intonation.

the G string is notorious for not holding tune, but a decent setup will minmise this issue
#7
check the nut, then the machine head. Whats happening is that the string might be slipping from the post.