Vintage Synth Repair

The title pretty much says it all. The display will show hex
gibberish, nothing else seems to respond. I bought this new, used it
for many years, and about five years ago, it just started doing this
during use. The factory reset-reinit procedure no longer seems to
work. I have read that there is a lithium battery, that can leak on a
triple-layer board, that pretty much makes it toast, as the middle
layer can't be cleaned up.

Suggestions?

thx
Scott S.