Roland JP-8000 repair
After many years of use my beloved Roland JP-8000 synthesizer unfortunately started to show some unpleasant problems.When turning on the display would show "Memory damaged", meaning the user patches were lost. Also, the audio output volume went low and bass-heavy patches sounded distorted, even when the main volume knob was just at the mid-position.
Here are the steps I took to track these issues down and to finally solve them:
1. Replacing Jack board capacitors
My first assumption was that the electrolytic capacitors on the audio jack board have gone bad since this board is located in close proximity to the power supply and may be affected by its heat dissipation. So I replaced all the electrolytic capacitors on the jack board with new 105°C variants. Unfortunatley this didn't improve the sound in any way.
Jack board after capacitor replacement; no change in sound
2. Replacing Main board capacitors
I then took out the main board and replaced all electrolytic capacitors around the DA converter (marked yellow, see image below). Additionally I renewed two capacitors near the connector CN3 (marked red). This finally brought back the original sound of the JP-8000. Some notes here:
- SMD capacitors must be unsoldered very carefully using a not to small soldering iron and and a good amount of flux to avoid damaging the PCB pads.
- The 10 electrolytic capacitors around the DA converter are all of spec 10µF/16V.
For replacement I used Panasonics FK-V 10U 16. - The 2 electrolytic capacitors at the connector CN3 are of spec 22µ/16V and 100µF/6,3V.
For replacement I used Panasonics FK-V 22U 16 and FK-V 100U 6.3B, respectively. - It's recommendable to also replace the other capacitors of the 5V/+15/-15V voltage rails, but this isn't necessary in the first place for solving the sound issue.
Main board after capacitor replacement; battery holder for the CR-3032 on the left
3. Replacing Backup battery
In order to get rid of the "Memory damaged" message on startup, I replaced the CR-3032 cell on the main board and performed a factory reset.
4. Pitch/mod/ribbon controls
After some testing I noticed that the pitch/modulation controller and the ribbon controller didn't work anymore. First I suspected that I had made some soldering error or maybe connected the internal cables wrongly when putting everything together again. But fortunately, the solution was more simple here. The pitch/mod/ribbon controls just needed to get re-calibrated. This can be done by entering TEST MODE on the JP-8000.
TEST MODE category 3: Pitch Bend / Mod Wheel calibration
In order to enter TEST MODE the buttons [OSC2 SYNC], [-12dB/-24dB] and [FILTER TYPE] need to be pressed simultaneously while powering the synth on. The categories 3 "Bender" and 4 "Ribbon" allow to calibrate the respective controls using the buttons [LOWER],[UPPER],[KEY MODE] and [UP]. After proper calibration the pitch/mod/ribbon controls work as intended.
Finally the JP-8000 is functioning like new again and I'm looking forward to many happy hours of fiddeling with this wonderful synth.