A Siemens AED four-circle diffractometer has been fitted with a Si(Li) solid-state detector (SSD) interchangeably with a scintillation detector in such a way that the whole 25 kg SSD package is driven by the 20 arm with no more strain or stepping errors than are experienced with the scintillation detector. Better energy resolution (elimination of 2/2 without significant intensity loss) and lower background noise, as compared with those of a scintillation counter, are obtained. The reproducibility of the TDS measurements made with this SSD system is within counting statistics.