MC-501 Will not Remote Start
Factory-Recon'd '501 came last week and even though the knob on the right would power up the amp, using the remote start would not. The red LED for Remote would light up, but no matter what combination of remote cables and sockets tries would not fire her up.
Even though the shipping container is in perfect shape, sending the '501 for a trip from Tampa to upstate NY is out of the question. Two different carriers already cracked glass on a C-28 and an MC-352, all within the last month!
So the amp came out of the box and on to the bench. Lotsa terrycloth towels is the way to go. As the amp is rolling over on its back to get the bottom plate yanked there is the unmistakeable sound of bits and pieces tumbling inside the amp chassis.
Disassembly starts with the remote board and a magnifier inspection looking for cold solder joints, then moves on to yanking the entire front panel, then the amp modules and moving on to the autoformers.
Removing the transformers revealed that one of the rivets holding the threaded transformer case securing screws was snapped. The nut just turned and turned inside the chassis. Best idea was to remove the outer part of the rivet and use a 4-40 stainless allen screw into the hole of the securement stud.
The debris was found in the undersides of the output autoformer: Little pieces of transformer potting compound had cracked off the edges of the dried compound right near the wires as they emerge from the tar-pit and were flopping around. Whew! It coulda been much worse. Putting the chassis back together gave rise to a warnig for everyone who wants to work on their stuff: The edges of the stainless chassis metal are like little razor blades. Especially when you need to jam your hands into tight spots to start hardware. First blood-Hmmmm.
Using a continuity setting on a DMM, the tip of a remote cable was used as the signal injector and the circuit was traced through the J-5 connector on the input board, throught he connectors on the right channel amp module and into the power supply board. There the problem ended. The mddle connectors on the power supply board are J-14 and J-15. The plugs are not lettered and look exactly the same. You got it: The plugs were jacked in backwards, meaning P-14 went to J-15 and vice versa. The amp would still play in manual mode but the +5 VDC start signal would never reach the optoisolator's LED pin 1 as the P-15/J-15 is not redundant.
A bit of Windex to wipe off the blood, a bit of Wax'n'Feed to nourish the walnut and she's back in shape, operation normal.
Hal