Quality Systems reported a 74% drop in net earnings for the second fiscal quarter ended Sept. 30, to $73,000 from $286,200 a year earlier. Revenues decreased 19%, to $2.6 million from $3.2 million for the like quarter of the year before. According to the company, the major factor accounting for the decrease in revenues and earnings for the quarter was a reduction in the number of large systems sold to medical group practices. For the first six months of the fiscal year, the company posted net earnings of $322,100, a 7% decline from the $347,200 reported a year earlier. Revenues rose slightly, to $5.3 million from $5.2 million last year. Quality Systems, based in Tustin, sells computerized information processing systems to medical and dental group practices.