Roksan Turntable Repairs
Roksan Xerxes Power Supply Repair
Power supply units for repair, one had 2 push buttons on the front and the other a single switch to change speed, these units generate a large amount of heat in an enclosed case and dry out the electrolytic capacitors and fry the output IC's / transistors.
In more detail:- the xps\2 as they are designated are in two designs as described, the 2 button has a standby position, this type uses 2 separate crystals and filter channels to generate the frequency for the 2 speeds (50Hz and 67Hz). These are fed to a pair of audio ics which drive the motors 2 windings, the other type with the single toggle switch changes crystals over (with the switch) and uses a common filter to feed a power op amp circuit consisting of 3, TO126 type transistors for each motor driver. The audio ics are the LM1875P, the filter ics are the LM324, there are 2 voltage regulators on the same heat sink. The pre-sets set the +\- voltage up and usually disintegrate with the heat. The o\p transistors used in the other type are BD140, these should be replaced with TIP30. Adjustment is provided to set the o\p voltage the same for each 'phase'.