Problem: Yamaha DX11 synth powers up with a message about the RAM battery requiring changing, and the internal voices appear to be corrupted.
Solution: Firstly replace the battery. This involves removing the bottom cover screws and the main PCB screws to access the top of the main PCB. The battery is soldered in and is a CR2032 type. The best option here is to use a 20mm button cell socket, to allow for future battery changes. Desolder the old battery and solder in the socket. You may have to adapt the pins to fit the spacing in the circuit board, but this will depend on the socket. Take care to get the polarity correct, it is marked clearly on the PCB.
Now re-assemble and switch on. The RAM battery message should be gone. If you are lucky, the voices will be intact and there's no more to do. However on my unit, which had been in storage for several years, the voices were corrupted. It appears that these are stored in RAM, but can be initialised from the EPROM. Firstly set the RAM memory protect to OFF. Now press the EDIT button and hold it down, then press the 16 and 32 voice select buttons together and release. The LCD screen should show a RAM test message. Pressing the YES button will test the RAM. If the test passes then a voice initialisation message will appear. Press the YES button to initialise the voices. Now power off and on again and the voices should be restored to RAM.
The performance RAM memory, however, may also be corrupt and there does not appear to be an internal initialisation mechanism for this. If you have a backup of the performance settings they can be loaded using MIDI sys-ex. If you do have a copy I'd be interested to hear from you to add it to this article.