Diagnosing Hum From Fender Rhodes Amplifier

Video Transcript

Hi I'm Larin Parker with Expert Village and we're going to take a look at the source of the hum inside of this Fender Rhodes that I showed you earlier. What I've done is I've opened it up, the back panel of the keyboard comes off, there are a number of screws. Whole bunch of them in fact, and then this panel which is normally connected up here and wired into the speakers and some of the amplifier circuits with the connectors is connected into it. That normally sits up on the side like this, with this power transformer underneath and this case on. I've taken off these screws, and here's just a really, really, really important point. If you?re going to take something apart, try and keep track of the screws. There are a lot of screws in taking apart this piece and one good idea is to use empty pill bottles or altoids tins to keep the screws in. Especially if you're going to keep something disassembled for a while. Furthermore, if you're not sure where these are going to go when you have to put it back together. Absolutely take some digital pictures of it. Use your cell phone camera; use your digital camera, whatever. Here we have, I'm almost super, super, super, super sure the cause of our hum. Right here we have a three thousand microfarad capacitor and we have another microfarad capacitor and these big conical capacitors that look like this, back in the sixties they were built like this. This is paper and metal, wrapped around in layers and then soaked in mineral oil. As soon as you see these in any type of old gear you know that's probably going to be the source of the hum. Because that mineral oil starts to evaporate over the years and as something becomes forty , fifty years old, they dry out and they no longer provide the function that they were suppose to provide which is to filter out that sixty cycle hum and to provide clean power. Without clean power all the circuits inside of this instrument waver up and down to the sixty cycles that they're getting out of the power supply. No matter how great everything else is in this keyboard you're always going to hear "bahhhhhh" Most problems in most vintage gear I see, especially radios and amplifiers come back to these mineral oil capacitors, paper and oil capacitors and the way you find them, is always look for the power transformer. In this big instrument you can see the power transformer is in this assembly so I knew to open up this assembly and that's where I was going to find my capacitors. If I go to the store I'm going to buy a three thousand microfarad capacitor and see it?s rated at fifty volts DC and another three thousand microfarad capacitor at fifty volts DC. It doesn't matter what type, how big they are. In fact modern ones might only be this big. If I solder it back into the same wires that it?s soldered to right here then I'll be in much better shape than I am right now. These are my culprits, if anything is going to go bad inside of a power supply, its going to be these mineral oil capacitors.

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