Guitar Synthesizer Repair Tips

Erratic or Unreliable GR-700

What seems to be the problem?

Perhaps one day one string on your GR-700 suddenly stops working. Or you can hear the string, but it plays very softly, followed by intermittent bursts of noise. Or you turn the GR-700 on, and after a few minutes, it starts making loud noises. Here is an audio example of one kind of GR-700 failure.

You most likely have a failed 80017a VCF/VCA chip. Here is a list of typical 80071a symptoms:

Erratic or sudden loud noise from synthesizer output, particularly after 10 minutes of powering up.

Note hang-ups or long sustain.

One synth voice will not respond to filter or amplifier changes.

Unstable operation.

One particular voice or string will not sound, "D" string, "A" string etc.

The 80017a chip was a real workhorse for Roland synthesizer engineers in the early 1980s. This one chip contained both the classic, driving -24 dB voltage controlled low-pass filter with a smooth voltage controlled amplifier. By placing all the components on one chip, Roland was able to keep the classic sound of their analog synthesizers across various products, with low production costs. Almost immediately Roland knew they had a problem on their hands, and changed production methods. Each 80017a chip has a batch, or lot number, printed on them. Chips labeled 48 and below are very, very prone to failure. But more recent chips can simply fail over time.

If one string does not sound, make certain that it is not your 24-pin cable!

An easy way to determine if you cable is working correctly on the GR-700 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.

80017a VCF/VCA Repair


Interior GR-700. Voice board is on the bottom, and the VCF/VCA is on the far left.	Interior MKS-30. The MKS-30 pc board is almost identical to the GR-700, with a few more chips.	Close-up of the 80017a. Notice the nearby trimmers for Gain, DC Balance, Resonance and Cutoff.	The top arrow shows the channel 6 (low E string) label, the bottom label points to the empty channel 6 80017a socket.

Repairing a GR-700 with a failed 80017a will take a bit of patience, and is not recommended as a first time electronic repair. To open the GR-700 up, remove the side panels, and the front most bottom three screws. The lid will then swing open. The 80017a chips are on the front, left-hand side of the bottom (voice) board. These chips are unusually large, long, and labeled "80017A Roland."

After you have located the failed chip, you can remove the voice board by removing nine screws and unplugging the connecting cables. Remove the failed chip and replace with a working chip. As I mentioned before, removing the failed chip will require some solid soldering skills and patience. When replacing the 80017a, it has a very unusual pin configuration which insures that it will only install in one direction.

Channel and String Identification

It is very important to correctly identify the failed 80017a chip. The chart below shows how the guitar strings map to the channels inside the GR-700:

Channel 1 = High E string.

Channel 2 = B string.

Channel 3 = G string.

Channel 4 = D string.

Channel 5 = A string.

Channel 6 = Low E string.

80017a in Roland Schematics:


Detail from Juno-106 Service Manual.	Detail from GR-700 Service Manual.	80017a block diagram from Juno-106 Service Manual

Additional Resources for the Juno-106/80017a Repair:

Below are links to download a Juno-106 service manual, to download a pdf file from Roland on the 80017a failure, and a MKS-30 main schematic.


Juno-106 Service Manual.	Roland Service Note	MKS-30 Schematic	Juno-106 Failed Chip Test Procedure.	Juno-106 Calibration	GR-700 Calibration

Above are various technical documents to help with your repair. I have added documents here on calibration. When the 80017a chip is replaced, the small trimmers around the chip may have to be adjusted. These trimmers adjust the level, DC balance, resonance and filter cutoff for each chip. Level controls how loud each chip is, Resonance fine tunes the amount of feedback resonance, Filter Cutoff is a fine tune control for the low-pass filter cutoff. Finally DC Offset adjusts the start and ending output of the chip so that when the sound stops, the amount of voltage is zero.

The synth will work without making these fine adjustments, but you may find one voice louder than another, or you may hear soft clicks as a sound decays, indicating some DC offset. While the technical documentation provides specific procedures for setting each chip, most experienced technicians rely on their ears for the final judgment. Also, Roland tends to be cautious with their recommended settings, so users may use these adjustment options to expand the tonal range of their synth.