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Hello, new guy here.
I have a 4002 series 5513 that I am overhauling, and everything was going quite normally with the job. I had already disassembled the platter motor, cleaned it up and overhauled it, and all appeared to be well with it. It was smooth and quiet. Platter rotated normally.
I then worked on the tonearm, and had it all reassembled. I went to test before moving on to another area, when I found that the platter motor wasn't working anymore. Really? Dead spot. Strange, because the commutator and brushes are in reasonable shape. OK, give it a spin and it... spins BACKWARDS!
What?
Nothing had changed from when it was spinning correctly an hour before. No disconnects from the main board, no anything. I removed the motor, took it apart again, all is beautiful. Coils each measure about 22 ohms at the commutator contacts, can't find any bad solder, can't find anything! I'm working from a pretty bad PDF, but I took a look at the motor drive circuit and compared it with the unit and all looks correct. 9 volts from the transistor and about 6 volts on the other side of the motor via the IC, for an operating point of about 3 volts. Connections look to be correct (they haven't changed)- red to the +9, blue to I forget which pin on the IC, white to the tach input on the IC.
And yet, this motor now runs in the other direction. I must say that I have never run across this in any instance of anything I've ever worked on. It's like there's a ghost in the machine. Spins backwards with a dead-spot that has no apparent cause.
If anyone has an idea of what might be going on here, I'd sure like to hear it. And if not, are there suggestions for motor subs on these? Normally I'm pretty good at puzzles, but this one just makes no sense whatsoever.
If the motor is of the type with an electronic board inside that is soldered off two pinsto access the rest of the motor innards, commutators etc., you got those two pins switchedby inadvertently rotating the inner parts 180deg when you put it back together.If that is the case, take apart again, rotate the innards and put back together.
Martin
Exactly. I now trace little marks with a permanent felt pen to be sure to re-align the motors correctly. Otherwise it's just a matter of luck!
Also, it is sometimes difficult to find CCW motors, so this can be done on purpose!
Jacques
Thanks for the replies.
Yes, in most cases this is exactly what I would think, as we've all no doubt done that. But in this case, the motor is not electronically governed, it's externally governed, which is why one can have pitch control.
It's not possible to reassemble this motor incorrectly, and also recall that everything was working normally before I started on the tonearm. Something happened in between those two moments of time. The platter was spinning in the correct direction after the overhaul.
The motor has three connections. Two go to the brushes. There are two coils inside the motor to serve for the tachometer. One is wired across the two brush terminals. The other is tied to the negative (blue) terminal and the other side of it is where the tach connection (white) comes from.
I feel like I'm in the Bizarro world. Can't find anything wrong, there's an unexplained dead spot, and the motor spins backwards (CCW). Next step is to disconnect the tach coils from the motor connections and see if those are somehow influencing anything.
This is just so weird.
Again, has anyone found a useable sub for this motor?
Check that the wire colors in the plug match with the lettering on the main board.There's usually a marking of red or black to match the nearest wire in the plug.
It's fixed, and you won't believe what the issue was. I had forgotten that I did indeed take the motor apart again a second time (it needed more oil in the lower bushing) before I had moved on to the arm without testing the unit after reinstalling the motor. I broke it. I discovered this because I kept thinking about how the motor works and started thinking about flux lines inside of the motor and how they might matter with respect to timing.
It turns out that the relationship of the ring magnet to the windings matters in a way that I did not know about. I always presumed that the number of poles and their orientation would have been symmetrical in relationship to the outer housing, such that it would not matter in which of the three positions (there are three screws that hold the assembly together, and no registration aids) the housing was placed onto the motor with respect to the brushes. If I were making a motor, that's how I would do it. But that's wrong. It does matter. In this motor, if you get the housing rotated to the wrong spot in relation to the brushes, the motor will run backward with irregular torque and might even have a dead spot like this one did. In fact, you CAN reassemble this motor incorrectly, just not in the commonly mistaken way of reversing it 180 degrees.
Wow. Learn something new every day!
"The music is reversible... but time is not! Turn back! Turn back....!"
Good job !
Lesson learned is to mark everything as you take it apart.