An electronic chassis supports a plurality of modules each provided with a small pin-point light such as a light emitting diode which will be energized only so long as the module is functioning. A back panel for the chassis in turn is provided with a plurality of observation openings respectively dimensioned and directed to be in line of sight alignment with the light emitting diodes on the plurality of modules. The arrangement is such that no ambiguity exists as to an opening and its associated module. Indentifying characters either numbers or letters are provided on the modules so that they can be visually distinguished from each other and corresponding identifying numbers or characters are provided on the back panel adjacent to the opening so that each opening has an identification corresponding to the identification of only that module whose light emitting diode is in the line of sight of the opening. A consumer can thus immediately observe through the openings which one or ones of the modules are mal-functioning by the absence of light and immediately identify such module by the identifying information adjacent to the opening on the panel from which no light is visible so that a new module can be ordered without having to remove the back panel until such time as the module is to be replaced.