24-Pin Cable Repairs
If something is going to break on your GR system, it has to be the cable. These cables are thick, with 24 conductors, and after a certain amount of movement, some conductors are bound to eventually break.
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.
I have found an excellent source of cabling to replace the ultra-rare Mogami cable found in the original Roland cables: Belkin F3D111-XX. The "XX" part indicates the length of the cable. The cable comes in various lengths, a ten foot cable is part number: F3D111-10. A fifty foot cable is part number: F3D111-50. These are high quality, data grade cables made by Belkin for computer switching systems. Just cut off the ends, and you have some premium, guitar-synth cable. This is the same cabling I used in all my GR projects.
Cool features of the Belkin F3D11-XX Cables:
An EXTRA Conductor: There are actually 25 conductors, so you have a "spare" conductor when one breaks.
Shielded Cable: Unlike the Mogami cable, the Belkin cable is shielded! I guess Roland felt that, with line level signals, they did not need shielding! In some circumstances, the Belkin cable may be quieter than the original Roland stock!
Color Coding: Rather than use the cryptic, morse-code like series of dots and dashes to identify different wires, Belkin uses easily identifiable color-coding.
Easy-to-find: I have no idea where to track down the original Mogami cable, and I am sure it is bound to be expensive.
All you need to fix your cable is a steady hand, patience, and good soldering skills. I have done this repair a few times with the original Roland C24-D cables. You open the cable up by removing the two, tiny screws inside the shell, next to the connector. Also, loosen the back screws so that the cable can easily slide through the shell.
Note: It is impossible to open the later, more universal Plastic hooded cables. The connectors are potted, and you will destroy the shell in the process of opening. Here are some photos of a cable repair I did using Belkin F3D111 replacement cabling: