Sorry guys – not a lot more I can say.
If you have a second-hand machine, it may have unknown problems. People sometimes sell things rather than fix them, and surprisingly, often fail to mention any issues.
These boxes may have well over 1000 presets, so it is likely that a small number of them are either broken or unsuitable for a given source material. Given the wide range of alternatives, and a desire to keep things stable, we do not rush to repair or change them.