Bob the Tech Audio just completed this McIntosh MC2125 repair. The unit had intermittent outputs which were hard to duplicate. After a good deal of listening we observed intermittent and uneven outputs left to right. Sometimes the channels were out altogether. When this happened, cycling the speaker switch on / off / on would sometimes resolve the issue. But sometimes cycling the switch just made the issue worse, or moved it from one channel to the other.
We found a coupe of issues. After pulling the covers we found significant damage to the connector/contacts at one of the driver board connectors. The packaging screws used to attach the pad to the bottom of the unit for shipping must have been too long. This damaged the connector and contact. We removed the contact, removed the damaged portion of the connector, and reattached the wire directly to the driver board header.
The other issue was in the speaker relay. The relay must have been serviced previously, it was not original. However, the replacement part was a 24V device, which is a lower coil voltage than the original relay. The previous service failed to install a critical dropping resistor. In this application, about 42V is applied to the relay coil. The over voltage would cause overheating / damage to the relay coil, which may have been the cause of the intermittent audio. We replaced the relay with a new one, and we added the appropriate dropping resistor. After installation of the relay and resistor, we verified operation and about 26V across the coil. This is well within the design range of the device. This relay should last a good long time.
For your McIntosh MC2125 repair needs, contact Bob the Tech Audio.
