I recently purchased a Roland MKS-80 in need of repair. Several things were wrong with it including the tuning knob, dynamics slider and “insert cartridge” errors when trying to change the patches from the front panel. Without being able to tune the synth or utilize the dynamics, the instrument was effectively unusable, but I decided to buy it anyway in the hope that it could be repaired. After several days and more than thirty hours of research, parts swapping, and troubleshooting I managed to get it working properly. Read on for an illustrated story of the repair process and audio from the fixed unit.
Estimates for repair were rather high, so before handing it off to a technician I decided to see if I could manage the job myself. This was a far more technical challenge than I had ever attempted and it didn’t go well at the start. The first step involved swapping out a an integrated circuit per the advice of a local synthesizer repair tech. The IC was an eight pin dual comparator. I removed it and put in a socket for the new chip, then replaced it with an equivalent component. Unfortunately this had no effect. I studied the circuit diagram with a friend who suggested that it could be caused by a second IC. This time it was a dual operational amplifier, also eight pins. Once again, I socketed the PCB after removal to make it easier to try other ICs and once again, no change occurred in the operation of the device.
I needed to go back to the drawing board. Although I had successfully metered the potentiometers for the dynamics slider and the tune knob, I decided to take a closer look at the panel board based on a suggestion from the technician at the Synth Spa, a specialty synthesizer repair service that operates via eBay. The panel board looked fine, but during another test I noticed that if I pressed down firmly on the dynamics slider that the pitch would change slightly. Further testing showed that if I held down the dynamics slider I could tune the instrument with the tune knob. This led me to suspect that there was a dry solder joint on the slider. Another clue was that the dynamics slider was bent, perhaps from a fall or hard knock. I heated up the joints and applied new solder, but not only did the original problem persist, but I could no longer press down on the slider and hear the pitch change.
This was frustrating to say the least. I was ready to give up and hand it off to someone more qualified than myself. Instead, convinced that the dynamics slider had to have something to do with it, I pressed on, removing the slider from the panel board and testing it again. It worked as expected. All that was left to try was to reinstall the slider and hope for the best, but during the re-installation I noticed that the solder would not stick to the top pin. I got up close to the PCB and looked carefully at the pin hole and saw that the metal track around it was gone. The panel board had been damaged by whatever caused the bend in the dynamics slider and when I removed it the cracked metal track must have come off the PCB with the slider.
Now that I suspected what the problem was I attempted to make a repair. The top pin of the dynamics slider went to two other locations on the PCB; pin one on the tune knob, and the first pin in the socket that connected to the CPU board. I cut a length of wire that would reach from the tune knob to the dynamics slider and finally to the socket. I stripped the wire on the ends and remove a small piece of insulation from the middle of the lead. I attached the middle of the wire to the top pin on the dynamics slider and then attached the ends to the tune knob pin and the appropriate pin on the CPU board socket. I secured the lead in place with some solder and tested the instrument one more time. Finally it worked! The repair is a bit of a hack, but easier than trying to find a replacement panel board. Here’s a sample of what I’ve been producing with it.
Roland MKS-80 Fixed