Hello,
I have owned both the Line 6 Variax 700 Acoustic and the Electric 700 models for many years. Recently, I had a piezo pickup fail and I had it replaced by an electronics repair shop authorized to repair Line 6 products. I have no idea what you have experienced with your model, but if you research online or call Line 6 with a gentle, patient, and respectful manner, I think they will be able to assist you. We've all been frustrated and angry over electronics systems that are beyond our comprehension. And it's a real freak-out if it fails you on-stage, and no one doubts that.
Apart from the fact that I had to buy 3 new copies of the Acoustic 700 when it first came before I found one that wasn't faulty from the get go, I've had no problems, other than that piezo going out. But anything that is 15 years old in electronic years is likely to be susceptible to board failures. You know that printed circuit boards took over the amplified market so that the solid state amps are fairly reasonable. They are more susceptible to cracking with age and damage from sudden changes in temperature, but they've saved us a lot of money. But to get all those modeling options in a hand-wired guitar just isn't possible. Know what a hand-wired amp costs these days? I can't afford them. I love both these first modeling guitars and I hope you get some satisfaction. But look at the Gibson Robot guitar and the Minitune 2014 Gibson Les Paul models and subsequent Tronical Tuning systems from Germany. All of these things have their problems; nothing new to see, here. Go back, please, to Line 6 and ask for help. If they can't help or won't (because they've been yelled at?), go back to real guitars that are hard-wired. Stay away from printed circuit ANYTHING, if it's reliability you seek. But If it's something innovative and new, something that pushes boundaries and is really exciting, there's no other direction we can go, other than continue to buy either the old reliables or take chances on the new. I buy both. I just don't expect the same thing from both types; it's a reality.