The power supply filter cap has most likely crapped out. The bottom has 6 #10 Torx screws. Remove the bottom housing and remove it with the top facing down. The transformer is not anchored it is just sitting in a small plastic box on the top housing. There is a 470UF 40 volt capacitor about ½” diameter with axial leads under the printed circuit board.I would try paralleling it with a new cap to make sure it is defective. To replace it the board needs to be loosened, there is a power transistor using the mounting chassis as a heat sink and to get the board up enough to get to the capacitor out you will need to remove the screw. The transistor is insolated from the chassis so make sure you but everything back correctly.The red dot is the positive lead of the capacitor and the black dot is the negative. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Put a meter or scope across the track power and see if you have AC ripple.
It's always using pulse power, until the speed gets high enough. Do the locos stop buzzing if they go fast enough? And which locos do it and which don't? Locos like Athearn BB tend to have very loosely assembled motors with the magnets not even glued in and will buzz if you look at them sideways. Other locos with better quality motors have the motor securely assembled and don't really buzz.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Nope. It happens with momentum turned on and off
Building my first layout, 4x8 contemporary urban area in HO scale
Do you have Momentum turned on? That is pulse power and could be the culprit. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
I have a mrc tech II and I have the dc output connected to my ho track, and all my locomotives run fine on it. But my dc locomotives make the 60hz humming sound like ac even though it's running on dc. why? Is it a problem?