Beomaster 900

20th October 2009

This receiver gave no results and was getting hot because one of the AD139 output transistors was short circuit. After replacing this the set worked but there was a hum in the background and the regulated supply to the amplifier was high at 27V (it should be 22V). The SP1446 regulator transistor had also been damaged, replacing this removed the hum and allowed the output voltage to be set up correctly.

The original transistors used in the Beomaster 900 are becoming difficult to find but the AD139 can be replaced by an AD162 (providing both transistors in the affected channel are replaced) and the SP1446 by and AD149, both of which are still widely available. [Beomaster 900K, Beomaster 900M]