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Klaas Robers wrote:Harry, if possible try to rotate the deflection coil while it is working, or do it in small steps.
Observe what happens on the screen. As the cathode ray tube is circle symetric it is expected that the shape of the scanning field is not affected by the rotation of the deflection yoke, so the distorted square keeps its distortion, in whatever position the yoke is. This prooves that the deflection error is in the yoke, or the sawtoothed deflection currents.
If not, if the shape of the distorted square changes, there is something in the picture tube or its surroundings. May be that you used iron bolts in the front of the monitor, that are magnetized. Such a magnetic field may distort the square, but it you rotated the yoke by 180 degrees, so all acannings are reversed, the distortion is still on the same position of the screen. Then search for this disturbing magnetic fields, and if you found them, try to eliminate them.
If the pattern on the screen simply rotates with the rotation of the yoke, then the error has to be the yoke itself, or the deflection voltages and currents. For me this would be the next step.
Klaas Robers wrote:Harry, do these deflection amps use a low ohmic resistor from the bottom of the deflection coil to ground? And feed back from that point to the input of the opamp?
Those are the better circuits.
Klaas Robers wrote:Harry, the deflection amplifiers expect at their inputs a sawtooth that goes from -1 volt to + 1 volt. For the vertical deflection this is a kind of DC voltage that very slowly rises or drops. If you soldered a capacitor in that signal path, the slowly changing voltage is converted to a DC voltage of about 0 volt. So that will not work.
Use you oscilloscope to check the input signals to the deflection amplifiers.
They should be linear sawtooth voltages going from -1 volt to + 1 volt and/or reverse. Then look at the voltage across the resistor at the bottom of the coil. This should have almost the same shape, although somewhat larger or smaller. The VOLTAGE going to the deflection coil may have a strange shape. But it is not the VOLTAGE that does the deflection of the beam, it is the CURRENT. This current goes to ground through the resistor of 5 ohm and makes again a voltage of it. In this way you can monitor (see) the current.
If the horizontal deflection works, you may test the vertical deflection by connecting the wires of the vertical coil to the output of the amplifier. Of course after disconnecting the wires of the horizontal coil.
[/quote]The resistor of 100 ohm is indeed dependant of the resistance of the coil. It has a value 10 to 20 times the resistance of the coil that he is switched in parallel. But if one of the coils has a resistance much higher than say 10 ohms, then see if you can modify the coil. Those coils are always made up of two coils, that are switched in series or parallel. I remember that you wrote about a coil of 40 ohm. That will be two half coils in series. If you circuit them in parallel, the resistance drops to 10 ohm.
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