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Beogram 4002 ground

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cray_guy
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cray_guy posted on Thu, May 7 2020 11:47 PM

I'm trying to finish restoring a Beogram 4002 model 5503.  The AC motor seemed a bit erratic so I put an oscilloscope on it and I was not getting the expected clean sine wave.  Instead, it was a bit choppy.

Following signals around I found out that my DC power had a pretty big ripple in it.  I grounded the negative side of the power supply capacitor(s) to the motor housing and all the issues disappeared.  So it seems that there was not a good clean ground made through the wires that go from the power capacitors to the motor..

I kind of feel like it is cheating to put in a separate ground wire to the chassis, but things to run correctly if I do that and I get perfect sine waves for 33 and 45.  So it looks like an internal motor problem.

Anyone seen this?  Should I just go with the kludge?

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sonavor
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It is good that you discovered what the probable source of the problem is but I would recommend trying to find where that missing connection is. If you find the original path is something something that would be unreliable to repair or some internal connection you can't get to then you can rest assured that your rewiring solution is necessary. On the positive side the experience forces you to dig in and learn more details about the Beogram. If the problem is internal with the motor I would contact Beolover as he is really good with rebuilding both the DC and AC type Beogram 400x platter motors.

-sonavor

cray_guy
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Thanks Sonavor-

Good advice.  I have to believe that the missing connection is inside the motor (which is screwed to the frame).  I can't see another path to ground for those capacitors.  I watched Beolover's video on infusing oil in a DC motor, but i'm assuming it applies to the AC motor as well.  It is pretty much a given that this procedure has never been done in 40+ years in this, so it is probably worth sending it in to get oil in there again.

Best,

Jeff

sonavor
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Yes, for sure. I have sent him quite a few BG4002 and BG4004 DC motors.  I have also had him restore two of the BG4000 AC motors. Well worth it and you won't have to worry about them for the next 40 years :-). Plus he fully tests the motors after the restoration.

-sonavor

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