Might sound wrong to you, but sometimes the caps are bad. Sometimes, they just don't get along with the boards. I had an engine I put a cap thing into, and it took over an hour of running, before the address change would stick!
So I put a MTH battery in that engine and it was fine. I moved that same cap to another engine and it also was fine. I left without making any other conclusions.
Maybe certain revisions of PS2 don't like the caps? maybe something in the board's flash or soundfile? I just don't know.