Bob the Tech Audio took on repair of this McIntosh MA6500 with broken glass and severe distortion. We also replaced the broken front panel glass. It turned out great and the customer feedback we received shows it.
There were a number of issues, some intermittent, that caused the distortion in this unit. A leaky capacitor in the -15V power supply made that supply inoperative. The -15V feeds much of the audio preamp circuitry and as a result directly impacts the signal quality. The original capacitor, and the rework to replace it, is shown in the first photo.
With the low voltage supply repaired the unit operated great – but intermittently. Further evaluation found several other issues, some of which may have been from prior attempts at repairing this unit. We found a missing nut on a power supply ground connection and replaced that. The ground connection would sometimes be OK, sometimes not, contributing to the intermittent issue. We installed the correct nut for a solid connection.
We found another issue where the B+/- power supplies were going live immediately upon switching on the main power switch. These should not come up until the standby switch is used to power the unit. In this case we found and fixed a damaged trace to the power relay. We also identified and replaced a faulty line driver which was activating the relay. With those fixes in place, the +/- supplies come up only on standby, as designed.
We found the last intermittent in the power supply in the form of a broken ground connection on the large B- filter capacitor. A picture is below. We’ve seen these joints fail before. Our theory is that because the parts are so heavy and tall that they can act as a lever, breaking the joints. This is especially true if getting bounced around in shipping, or if used as a handle to remove the board from the chassis. When the joint makes a connection everything is OK. When the capacitor shifts and connection breaks the supply becomes unregulated. These voltages feed the power amp and if not well regulated will result in heavy distortion. We wired the ground in and the power supply behaved properly and solidly.
The last electrical fixes in this unit resolved poor meter behavior and front panel lamps. A missing nut, which forms the meter ground connection, caused the meter issue. With that replaced the meter ground and meter performance was solid. We calibrated the meters and they’re now performing well. We replacedfFaulty front panel lamps with new to match original design.
This unit also came in with cracked glass. We moved the original pushbuttons, headphone jack, etc. to new front panel glass, shown below, and reassembled the unit.
Bob the Tech has serviced dozens of McIntosh MA integrated amplifiers. If you have a McIntosh MA6500 with distortion, broken glass, or in need of any other type of repair contact Bob the Tech Audio.
