If the image on the monitor screen is unstable. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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If the image on the monitor screen is unstable. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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I propose two options for solving the problem of "jitter, image floating on the monitor screen with a cathode ray tube", which is caused by the influence of external magnetic fields. The most cardinal solution to the problem is to purchase an LCD monitor, but this is not always possible.

The essence of the proposed methods is to create a magnetic field near the monitor or inside the kinescope with a vector that is out of phase with the external vector that interferes with normal operation.

The first option is implemented without disassembling and refining the monitor. This will require two network step-down transformers with a power of 10 ... 100 W. The primary winding of one of them (T1 in Fig. 1) is connected to a 220 V network, and the secondary (5 ... 20 V) - through a variable resistor R1 with a power dissipation of 1 W - to the primary winding of the second transformer (L1), from which the magnetic circuit has been previously removed. Coil L1 is placed on the monitor from the rear side (near the neck of the kinescope) so that its coils lie in a horizontal plane. Having set the monitor frame rate on the computer to 50 Hz, move the resistor R1 slider and achieve the least "floating" of the image. In case of increasing "swimming", the coil is turned over 180 °. As T1, the author used a step-down transformer from the Dendy game console power supply, and as L1, a 100 W transformer coil.

If the image on the monitor screen is unstable

The second option is somewhat more complicated: the external magnetic field is measured with an inductive sensor and a correction is made to the operation of the horizontal (and vertical) scan. Sensor L1 (as in the first version, the primary winding of a 100 W transformer) is connected as shown in fig. 2 to the monitor node where the horizontal sync pulse phase shift is generated (right-left image shift adjustment). I can’t give more detailed advice here, since everything depends on the specific type of monitor. I experimented with the Belinea 14" monitor.

If the image on the monitor screen is unstable

In my case, the interfering field vector (50 Hz) was vertical, so the image trembled horizontally (a heating main runs under the windows of the room and, apparently, a significant electric current flows through the pipes). The second option is better than the first one, because the magnitude of the interfering field may change over time, compensation occurs automatically, and the frequency and shape of the field may not correspond to the network one. However, the first option is simpler, and the effect of it was slightly better.

In conclusion, it should be noted that it makes sense to use the second option if the interfering field is uniform in the volume of the monitor. It will not effectively protect against pickups from the side of a transformer located near the monitor, since its field has a different effect on different parts of the monitor screen.

Author: A. Zhenzherukha, Stary Oskol, Belgorod region.

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