Repair Roland MC-4 Microcomposer Reparatur3. November 2019
Repair a leaky output or battery of a Roland JP-8000 Synthesizer – Tutorial – Reparatur24. November 2019
Today I write about a lovely piece of gear. Customer brought in this Oberheim OXBa with the following situation.
"Switches on, but no "musical" sound except some noise here and there."
I tested it immediately and found out, that the main problem was no sound was in the memory due to an empty battery. When I manually designed a sound it started to work. Having done that I found the keyboard wasn´t working quite well. Not all keys were working, especially not in the first instance, and the keys itself were quite noisy (bad key bushings). He asked me, if I can repair these issues and I said yesss...
So one thing to do was to change the battery. I did that 1:1, so I put in a new 3 volt BR-2/3A lithium battery. Then I tried to load in the preset factory file via the cassette interface, but that didn´t work at this point. So I decided to clean the keyboard and the switch panel first.
I cleaned all J-wires, the bus bar and the keys themselves. Here`s a picture of a dirty bus bar contact.
Here it is half way cleaned.
And here it is fully cleaned with an eraser first and then with ipa.
I had to replace two j-wires as they were already loose and broke off while cleaning. Nothing serious, this was an easy fix. I then changed all the key bushings and cleaned every single key and reassembled the keyboard and adjusted the each key.
Next was to clean all the potentiometer from corrosion, dirt and old grease.
All potentiometer worked much better, let's say worked great after refurbishing. While I am in here I took the change to replace the electrolytic capacitors on the from panel. Customer also wanted me to replace these old electrolytic capacitors on the psu board...
Now that I had the keyboard, switches and potentiometer cleaned I found out that the synth came back to life and sounds could be edited in manual mode. But some voices were detuned. While trying to adjust the tuning I found out that the red dip switch was corroed too so I had to replace it too. Now I could tuned the voice cards. There still was the problem that I could not load the factory sounds. I replaced some components in that circuit with nos and now that I could load the 120 patches it sounds just great to my ears (remember, I like club music ;)
There are lethal voltage exposed in electronic devices. Unless you know what you are doing, don’t try this. If you following along, you doing so at your own risk.
I’m documenting repairs for my reference and yours.
I do synth restorations and repair with a specialty in vintage synthesizers, drum computer and other vintage gear, based in Düsseldorf, GER. Get in touch about your synth situation!