Guitar out has no sound

Check plug on guitar for loose wire

There are only a few things that could be responsible for your problem. Dirty volume knob on guitar or amp. Faulty ground on all affected parts; including cables. I suggest you plug into a different amp with a new chord, and see if the problem still exists. This way you can quickly eliminate compnents & focus on the actua lproblematic one. If it still exists..you can assume it'sin the pick-up.

Have you checked a different cable?. Also, when you plug in the unit, there should be a "pop" if everything is turned on. If there isn't, the connection is bad someplace.

where the socket is for the cord to be plugged in, often the ground will come loose or break on the socket connection, you will need to take off the plate that conceals the electronics of the guitar and see if any wires have become damaged , this happens a lot when your using a patch cord with a 90 degree end going into the guitar , it puts added pressure on a already touchy socket.

If you are in the US, take a length of light-gauge wire (AWG 20-24) attach it to the center screw that keeps the cover on over the standard dual AC receptacle and to a screw on the back of your unit. This kind of problem often is caused by a poor grounding of the cover or chassis.

Try plugging another sound source into the unit. The buzz MAY be pickup of magnetic fields in your guitar pickup that clobber your notes from the strings. Bad guitar cables are another possibility. By putting clean music from say a CD player into the unit you can find where the source is. If the CD player generates the same noises, then likely you have a failure of filter caps in the amp or other component failures. Also make sure your guitar can't "hear" the amp as feedback can do strange things.

I personally use Seymour Duncan Humbucker pickups, and have never been disappointed. You might want to take your guitar up to a music shop and try it on different amps to see if your amp is your problem, or if it is your guitar's pickups or wiring. You could also try adjusting the height of the pickups until the sound you are looking for is achieved. I have also had guitar cables make a big difference in the sound. Make sure you have a good set of cables, and you may want to adjust the EQ settings of your amp to make up what the guitar lacks.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

i dont' see where this model has active pickups (guessing this is what you mean by pre-ampped).
The issue can be in a few places.

1) the strings could be too far from the pickups and the instrument needs to be tuned.
2) the pickups are bad
3) your jack is bad
4) the cable is bad
5) your equilizers are not corrected
6) your volume control is turned down or damaged
7) your amp is damaged

this is a small list of the basic possibilities.

If you want help from Roland you will have to register:http://www.rolandus.com/backstage/login.php That will get you access to full support and their email address. I think you are having problems with your GK-3 pickup. Make sure your string that you are having problems with is the optimal height etc. The adjustment for the GR-20 is in the manual at this link:http://www.roland.co.uk/assets/media/pdf/GR_20_Q_A.pdf Make sure your pickup is installed correctly and adjusted properly first. The manual is here:http://lib.roland.co.jp/support/en/manuals/res/1811530/GK-3_e11.pdf If you have everything adjusted and only one string is not working then I would guess you have a cable problem and the best thing is to contact Roland for advice. I didn't walk you through the adjustment because every installation for every guitar is different. Hope this helps.

If you unplug the guitar cable and STILL get the hum, the unit has a defect... return under warranty.

If the hum goes away when you unplug the cable, replace the cable and see if new cable fixes the problem. If it does, the cable has a bad shield.

If the cable didn't cure it, then the guitar has a defect. Remember that some guitar pickups are sensitive to the magnetic fields from the amps... only cure is to either use humbucker types or be a distance away from the amp.