Technical Information EMT 930
Adjusting the motor capacitor
The drive motor for the EMT 930 uses 3 phases. As the motor is driven directly with the mains
voltage, which normally uses Ground and one phase, there must be a created an additional
auxiliary phase. This is done with a resistor and a capacitor.
The capacitor (normally 1.75μF) is adjusted in the factory to a value, which gives a minimum
of hum in the machine. The adjustment is done by adding small capacitors.
During live time, the value of the original capacitor will change. This can be recognized by an
increasing hum, by a rising motor temperature and by feeling the motor vibrating.
Adjustment
Tools needed:
Millivoltmeter, Oscilloscope
How to adjust?
BE CAREFUL, BECAUSE YOU WORK WITH MAINS VOLTAGE!!!
DON’T ADJUST THE VARIABLE RESISTOR!!!
First, if your unit is equipped with a basket at the motor, unscrew the basket, to get access to
the capacitor.
Connect the voltmeter and/or the oscilloscope the output.
Put the needle in an empty groove. Now set the main switch in a position, which is normally
not fixed, between the leftmost position and the middle position (that makes the motor
running, but the turntable is not rotating). Now one can see the hum on the
voltmeter/oscilloscope.
A cheap way will be, just to add small capacitors to the large one, to find a minimum of hum.
But in some cases the value of the capacitor has grown, so that the hum will enlarge.
In that case you have to go a less cheep way and you might order a complete kit of capacitors
(including the large one) with the order number 9 930 902.
Then exchange the large capacitor, solder small capacitors in parallel to the large one, until
you reach the minimum of hum. Then fix the basket again and enjoy your hum free EMT 930.
H.-M. Fabritius, 31.08.00 作者: 铭友影音 时间: 2012-4-12 17:35 回复 wayned 的帖子