You should measure across the hot and neutral wires in an AC circuit. Sure you *can* measure from each wire to the chassis, but here is the problem with that in this scenario: Is your power cable stock and just two prong? If so the chassis ground is floating from the building ground. There’s no bonded reference to the “earth” that the neutral wire references. So it all depends on how they did or didn’t ground the chassis, and how the neutral wire interfaces the ground scheme of the device…remember AC power is Alternating Current, not Direct Current as with DC power. With DC power you have linear current flow from a point of high voltage potential (the positive side) to a point of low voltage potential (the negative or “ground” side). Think of water flowing over a water wheel making it turn. The wheel can then do work. This is analogous to DC power, where the water is the flow of current in a linear path and the water wheel represents a DC motor, though instead of water and paddles on the wheel you have electrons and coil windings and magnets. With AC you have current alternating cyclically in a positive phase and then a negative phase over and over…back and forth…push, pull, in a sine wave. So with AC power you have not only voltage and current to consider, but also frequency…the rate of the pushing and pulling. In the US that rate or frequency is 60 cycles or hertz. Think of the connecting rod in an internal combustion engine, or on the drive wheels of a steam locomotive…the rod is going up and down (or back and forth) making the crankshaft or drive wheel rotate. This is like AC power driving an AC motor. So when measuring DC voltage you have to measure between the positive side and the negative side (or “ground”) to measure the differential or *difference* between the high potential (positive) and the low potential (negative)…that’s what we are measuring with DC voltage, the difference between the positive and the negative or ground reference. With AC voltage we are measuring the amplitude or “height” above
and “depth” below the center 0V reference of the sine wave…think of the stroke of the connecting rod…the length of the travel up and down in total is what we are measuring with AC volts, because the rod does work in both directions. There are a couple different ways we measure it, but we don’t need to get into that here. So you want to measure between the line and the neutral wires. You certainly could measure to “ground” because, remember in my previous post I indicated the ground socket of a grounded outlet *should* be tied to the same ground reference as the neutral wire in the service panel, because the ground is just a safety backup in case the neutral wire fails, but before you use the ground as your reference for the hot wire you have to verify the ground socket is
actually bussed to the same reference as the neutral wire in the service panel, then verify the ground in the outlet propagates to the chassis of the device (typically via a three prong power cord), and that the ground wire in the power cord then positively bonds to the chassis of the device. If you don’t know those things, then you can’t rule out that there may be a voltage differential between the device chassis and the building ground because the chassis ground is “floating” (i.e. not referenced or “bonded” or connected to the building ground), and then if you reference the line wire or “hot” wire to the floating chassis the voltage reading will be the sum of the line voltage and the ground differential. This differential is typically pretty small, but, hey, if you have the neutral wire right there, which is the primary reciprocal path for the current in the hot wire, why not just measure across that and the hot? Hopefully that makes some sense. I know that’s a fair amount of detail, but you seem to have a pretty decent grasp of things so there you go.
It may be accessible, but it’s not likely a “fuse” per se, or some kind of replaceable component, it’s likely an embedded expendable link that when used is done. And beyond that if the link is wasted and you are still smelling hot electrical smell, the transformer is further damaged. A broken fusible link should cut all power from the primary coil of the transformer because when expended it breaks that reciprocal neutral path back to the power station for the hot wire. If it’s getting hot that means current is still flowing where it shouldn’t be, which suggests irreparable damage. But of course you’re always welcome to tear the thing open to look at the guts. I might do the same thing just out of curiosity, but my hunch is that is the only purpose that will serve; to satisfy curiosity. I think it’s most likely the transformer is irreparable.
It’s this one in this big thread:
https://homerecording.com/bbs/threads/tascam-m-___-story.270992/
So regarding the M-312B power transformer, your pic showing the side panel does remind me it looks like it is fabbed to mount multiple transformer assemblies depending on if it is an M-308, M-312 or M-320, and indeed it looks like the fastener spacing on my transformer is 2 15/16” x 2 3/4”! See pics below. Note the end of the measuring tape is on the 1” mark for better measuring accuracy, so subtract 1” from the result you see to the right end of the tape in the pictures:
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And as far as the dimensions of the assembly itself, my hunch is it will fit by virtue of the fact there are corresponding mounting holes on your chassis, but the height, width and depth of the assembly, if we consider the mounting surface of the assembly as the “bottom” is approximately 2 3/4”H x 3 11/16”W x 3 3/8”D. Here are pictures:
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