by Eddy Deegan » Sun Nov 29, 2020 12:51 am
I never owned a D50, but I did own a D10 and I have a feeling that the battery isn't the problem here. The corruption on the screen in the photos strays well beyond the data fields maintained by dynamic battery-backed memory.
If there is a chip/data fault it would be an issue with the ROM holding the hard-coded strings that form the labels for various voice parameters. As to which ROM that is or how to fix it I cannot say. The fact it works OK other than the display is probably a good sign but I'd be inclined to reach out to Roland and ask them for some input on which chip(s) to consider suspect.
They probably don't sell them any more but you might be able to find a dead or damaged D50 cheap on an auction site from which to salvage one or more replacement chips.
Before doing any of that, I'd be inclined to open up the case and see if there are any dry joints or cracks in the connections associated with the ribbon cable going to the LCD. It could be that the corruption isn't ROM based at all, but one or more bad connections are corrupting a bit or two of data being fed to the LCD, which would also explain the issue shown in the photos and would be a relatively easy fix (just renew the solder joints and/or add a fly-lead to cross a broken PCB track) if that was the case.