July 2021
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Roland G-202 G-303 G-505 G-808 Opamp Failure - Repair:

One String Stops Working

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.

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.

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, and you know your cable is good, your pickup is working fine, then your op-amp is most likely bad. If you get all six stirngs to output a synthesizer signal, but one string looses the hex fuzz sound, then it is almost certain that you have a bad op-amp.

The GR guitars use 4558 op-amps, available at any decent electronics shop, and they typically cost just a dollar or less.

Typical replacement part: STMicroelectronics 4558 operational amplifier at Mouser.com.

Here are some photos of a op-amp replacement I did on a G-303. Notice I installed an IC socket on the G-303 circuit board, to make future repairs or upgrades easy.

opamp repair opamp repair opamp 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.

Volume Control Not Working

The Volume control in the vintage guitars also requires an opamp. Failure of the opamp may completely kill the volume of the guitar synthesizer.

Roland G-303 G-505 G-808

A look at the schematic of the Roland G-303 G-505 and G-808 shows that the output from the master volume control is also sent to IC7, a 4558 DIP (dual inline) opamp. The opamp is configured as a buffer amplifier, to pass the signal unchanged to the synth balance control. This is critical, as in the Roland GR-100 and GR-300, is it synth volume, presented on pin 9, that actually controls the volume of the GR-300. Pin 8, or master volume, is not used. IC7 is also used to amplify the output from the humucker pickups to line level.

Roland G-202

The G-202 is wired in a very similar manner, except that IC6 is used to buffer the master volume control signal before it is fed to the synth balance control.

Roland G-33 G-88

The early bass guitar synthesizer controllers also use a 4558 chip, opamp IC5, to buffer the volume control signal.

Roland G-707 and G-77, Ibanez IMG-2010

The G-707, G-77, and IMG-2010 also use an opamp to buffer the volume signal. Unlike the earler guitars, which use the 4558 DIP opamp, the G-707 and G-77 uses the M5218 SIP (single inline) opamp.

Roland G-33 G-88

The early bass guitar synthesizer controllers also use a 4558 chip, opamp IC5, to buffer the volume control signal.

IC7, volume and normal guitar signal buffering opamp IC7, volume and normal guitar signal buffering opamp IC7, volume and normal guitar signal buffering opamp
IC7 before replacement. Underside of the electronics. Ready to solder 8-pin socket The new 4558 was mounted inside a socket, for easy replacement in the future.
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