Commented out missed connect(...) statements. In IDEASScalerView constructor: CLSSIS3820ScalerChannelView::sr570ViewModeChanged(...) signal, IDEASScalerView::onSR570ViewChanged(...). In VESPERSScalerView constructor: CLSSIS3820ScalerChannelView::sr570ViewModeChanged(...) signal, VESPERSScalerView::onSR570ViewChanged(...) slot.