Low width (by 2 users)

Same problem teleman enquired about. My wife said her monitor was fine when she left it, but when she returned an hour later the monitor width had reduced and is now only about 90% of what is required, even with the width set to 100%. I suspect a capacitor has failed, but before diving in blindly with no schematic was wondering if someone had already determined which capacitor (or other component) was responsible for this problem.