I have a takemine 523 12 string. recently, the preamp starting flashing arrows up and down, the tuner is inop and can't get sound through the amp. Any suggestions?

Good question, tuners can be simple and some are complicated
a basic automatic guitar tuner you would not have to do anything to the settings, just tune normal on the E string then slowly down tune to D most tuners are a little sensitive, so go slow
and one thing I always do is go lower than the note I'm tuning to then tune up tell it's correct, strings seem to stay in tune better
Hope this helps ?
and if you have time check back on my profile
I will be doing some video tips this weekend
showing tuning, and some basic guitar repairs
thanks for your time

It sounds like the guitar pickup may be faulty. It may be a loose connection on the which could be soldered easily or it may be damaged in some other way.

As this is isolated with your G string, I suspect the individual pickup unit is at fault.

if you have the adjustable bridge try moving it back a little bit. the g string is a heavy string and will tend to go sharp when you have the string height up a little. make small adjustments usually only one turn or half a turn at a time. take care to note your adjustments so you can always go back to where you started. turners are nice but the ear doesn't lie. if it sounds right it's right

looks like broken wiring from pickup to preamp - maybe on jack?

That is working backwards from what it should be. I suspect a wiring error. Since this is a recent purchase, do NOT risk voiding your warranty. There isn't any real good documentation on the tuner.
I am not sure which tuner you have HOWEVER with one type, the FIRST press will turn on the tuner with the sound going out as well till the tuner goes off. The SECOND press silences the sound and is tuner only, the THIRD press turns off tuner and passes the sound. This is different than a lot of tuners and you will need to do three presses to restore sound instead of the usual two.

Hi
Simply turn the tuner on using the power button. Play an open string note close to the tuner (no more than about 1/2 metre away) - for instance the low E on string 6.
The built in microphone will pick up the sound and, if your guitar is reasonably close to being in tune the led light labelled 'E' will illuminate on the lower scale on the tuner along with one of the three other leds to indicate whether the note is flat (b), in tune (green) or sharp (#).
Due to harmonics any or all of these three leds may flash but it is the one that is on the most that matters.
Adjust the tuning peg until the green is on constantly when you play the string.
Move on to the next string
Note - if the string is more than a semitone sharp or flat a different light may flash (e.g if the low E string is 3/4 of a tone flat the D light will come on).
If you wish to tune your guitar to another instrument that is not at perfect pitch (and perhaps cannot be easily adjusted - like a pipe organ) you can use the calibrate button to adjust the setting of the tuner. This temporary recalibration will be lost when the tuner is turned off.

Take it back to the shop where you bought it and ask them to set it up properly for you. It's an expensive guitar it should be supplied correctly set up.

Clamp it to the headstock of your guitar just like in the picture. Press the power button. Pluck one string on your guitar, the screen will light up with the corresponding note (standard tuning from largest string to smallest string is E A D G B E). The arrows will indicate whether the string is sharp or flat (too high or too low). More left arrows indicate that the string is too low, too many arrows on the left indicate that it is too high. Turn the tuning peg, slowly, on the corresponding string until you've got 6 solid arrows.
Here's a video
http://www.expotv.com/videos/reviews/16/154/IntellitouchPT1Tuner/275941

i don't really know what instructions you expected, although you should have received something for the tuner and amp. I suspect that you are new to playing the guitar, as, I don't wish to sound disrespectful, you would know what to do! So first, and again I hope not to sound like I'm treating you like a dummy, plug the guitar into the tuner input. Or if It's a piezo tuner clamp it to your headstock. Most tuners are now automatic so it should pick up on the string you are striking.Repeatedly pluck the same string til the tuner changes colour, or flashes, or some other indication to tell you the string is at pitch. Repeat the above for all 6 strings.
Then plug the cable into the amp input, switch it on, and bugger about with the controls til you get a half decent sound. ( thats what the rest of us do).Don't expext too much from this package, it is budget level, but of quite good overall quality.hope this helps