Marantz PM4000 Amplifier Repair

Fault Intermittent loss of sound when increasing the volume above 25% Mute LED Blinking and speaker protection relay turning off. This issue is often seen after a number of years of operation and is documented by Marantz in a service bulletin NBR MZ02-009 Dated Jul 2002. The problem is caused by poor grounding between the heat sink and the main Amplifier board. The solution is to Solder an insulated wire onto the ground end of R922 or R929, and connect the other end of the wire to a grounding eyelet and screw into place using the existing heat sink ground screw as shown in the video. The video also shows the board before the modification. Due to the age of this Amplifier the speaker protection relay was replaced and all dry joints on the main Amplifier board and input power board re-flowed. Particular attention should be paid to the input RCA connectors, and the voltage regulators for the plus and minus 15 volt supply and the 5 volt regulator for the Micro. Often dry joints will also be seen on the driver transistors in the output stages. Amplifier fully tested and DC Bas checked but no adjustment required. Amplifier working perfectly.