Guitar Synthesizer Repair Tips

Guitar Synth Pickup

What seems to be the problem?

You suddenly notice that one string on your guitar synth system stops working. The first thing you want to do is try another cable! Cable failures are the most frequent GR-system problem. If you do not have a spare cable, try jiggling either end of the connector, though the problem is most likely to be the end that plugs into your guitar. If the sound comes and goes, then you need to fix your cable. If not, then you most likely have a problem with an op-amp inside the guitar electronics. A more remote possibility is that you have a damaged pickup. At the bottom of the page you will notes on testing the elements in a hex pickup.

If you have a GR-700, an easy way to determine if you cable is working correctly is to press the EDIT foot pedal, followed by 4 and 8. This puts the GR-700 in tuning mode. Play each string on the GR-700, and you should see the display change for each string. The displays shows "1" for the high E string, "2" for the B string, down to "6" for the low E string. If the GR-700 responds to all six strings, then your cable is good, and most likely you have a failed 80017a chip.

Unless you have been moving the synth pickup around a lot, they usually do not fail on their own. Instead of a synth pickup failure, you possibly could have a problem with the electronics. Inside every GR guitar are a lot of small, integrated amplifiers called "op-amps." These due tend to fail over time. If you have a G-303, G-505 or G-808, you are in luck! These guitars are easy to test, and easy to repair. The other models of guitar synths are a little bit more difficult to troubleshoot, since they do not have hex-fuzz. While the G-202 has hex fuzz, it actually uses the same circuit for both the fuzz and clean signal, so the hex fuzz test will not work. Be sure to check out the bottom of the page for photos of a G-202 repair.

To find out if you have an op-amp failure, listen to the hex-fuzz output only. If all six strings work in hex-fuzz mode, then your pickup is good, and your op-amp is most likely bad. The GR guitars use 4558 op-amps, available at any decent electronics shop, and they typically cost just a dollar. A service manual (available from Roland) will help you figure out which one is bad, though you may just want to hire a technician at this point!

In any case, here are some photos of a op-amp replacement I did on a G-303 and G-202 with a "bad" guitar synth pickup. Notice I installed an IC socket on the G-303 circuit board, to make future repairs or upgrades easy.

G-303/G-505/G-808 Repair


G-303 Electronics interior, the arrow points to the failed op-amp.	Underside of the electronics. Arrow points to the pads to de-solder.	The new 4558 was mounted inside a socket, for easy replacement in the future.

G-202 Repair


The G-202 uses a crude dual layer design. Removing the op-amp also removed the surface pads	Defective 4558 op-amp with surface mount pads on still on pins 1, 3, 5, and 7.	Jumpers are wired to replace the connections made by surface wiring.	Connections to the VR (string level) trimmers.

To my surprise the Roland G-202 has a very crude dual layer circuit board design. Most dual board designs use a tiny metal sleeve inside the solder point to provide connectivity between the top and bottom layer. The G-202 actually has solder pads on the top and bottom of the board, so components have to be soldered twice.

After testing showed IC#1 on the G-202 to be faulty, I easily removed the chip. However, along with the chip came the solder pads from the top layer! After unsuccessfully trying to solder to the remaining traces on the top of the board, it had to run jumper wires. In this case, the jumper wires connected to the VR (string level trimmers) and to the junction of the distortion diodes and the output traces to the 24-pin connector.