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PSU Modification A30.2 070212 Written by Bjorn Holmqvist for the manufacturing industry. [email protected] Confidential ! This document is not allowed to show for third part without written permission from Primare Systems AB. If you got this document by accident, please delete immediately. This Document is Primare Systems Property. This modification solves a stability problem with the power regulation for the amplifiers driverstage. The first symptom for instability are Speaker relay flickering during startup, other symptoms might be distortion in the sound when amplifier is warm. If there is oscillation in (REG1, REG101, REG2, REG102) it can easily be spotted by monitoring the output voltage at test points (+-48V) with the oscilloscope. When servicing this circuit I also recommend that the resistance over R63, R163, R64, R164 are checked, if the resistance are different that the stated 4.7R please replace all four of them. 1. Remove mains power and the topcover. 2. Remove the heatsinks on REG1, REG101, REG2, REG102 in order to free up space for the soldering iron. 3. Solder 22uF/63V 105 centigrades capacitor in parallel with C18, C118, C19, C119 (or replace the original 3.3uF capacitor). Use a small soldering tip when carrying out this work and watch the relays ! 4. Put back the heatsinks on REG1, REG101, REG2, REG102. 5. Test the amplifier and measure the voltage at +-48V test points on both channels. Pics Note! I have used 10uF capacitors in these pictures, the correct value is 22uF. Left CH 22uF /63V Right CH 22uF /63V Overview //Bjorn Holmqvist