Restoring the backlight of the TFT monitor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Computer devices

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In article [1], a method was proposed for repairing the screen backlight unit of TFT monitors by connecting a capacitor in parallel with the faulty backlight lamp. The capacitor serves as an additional load for the monitor's power supply controller, which ensures that the entire device is put into operating mode. This method can only be recommended as a temporary means of recovery and as an opportunity to turn on the monitor for short-term work, since this does not eliminate the cause of the failure, and working on such a monitor with the lower or upper part of the screen darkened is not entirely convenient.

Fig. 1

The first step is to check the integrity of the secondary windings of the transformers of the power supply unit for the backlight lamps - as a rule, there are two of them. The resistance of a working winding is about 1000 Ohms. If both transformers are serviceable, then the failed monitor screen backlight lamp needs to be replaced. If a break in the secondary winding of the backlight transformer is detected, it can be repaired.

Let us consider below, using the example of the Prestigio P190T monitor, the technology for repairing a failed transformer with the factory designation BIT3105.

First, you need to carefully remove the adhesive tape from the transformer covering the frame with windings, and analyze the possibility of restoration. The secondary winding is located in eight sections of the transformer frame and contains (7 x 300) + 150 turns of winding wire 0,04...0,05 mm. All parts of the windings are impregnated with an insulating compound, and the frame and parts of the ferrite magnetic core (the closest analogue of EFD20 [2]) are fastened with a compound. When disassembling, you can save either the magnetic circuit or the frame. It is better to keep the frame - it is more valuable; only non-sectioned ones are offered on the market. But what if there is neither one nor the other?

It is necessary to position the transformer on the spread jaws of the vice so that the glued ends of the halves of the ferrite magnetic core are on the jaws, and the transformer frame is between them. With a sharp blow of a small hammer on the blade of a knife, the tip of which is installed at the junction of the ends of these halves, their outer parts are separated on one side of the transformer, as well as on the opposite side (Fig. 1). Then you need to carefully inspect all sections of the secondary winding. The darkening of one of the sections in comparison with the neighboring ones most likely indicates a break in it. You can verify this as follows: with a sharp scalpel, strip the insulation on the last turn of this section - only the insulation, without cutting the wire.

Using an ohmmeter, determine which terminal of the frame the circuit is in contact with: if at the beginning of the winding, then repeat the procedure with the next section until a break is detected. This section and subsequent windings to the end must be freed from the wire. A turn of wire is unwinded from the last section of the remaining part of the winding. The end of this wire and the wire prepared for winding is stripped of insulation and tinned using a well-heated soldering iron by pulling the wire under its tip, pressed against the PVC insulation of the mounting wire. As a rule, 3...5 pulls are enough.

The tinned ends of the wires are soldered together, the soldering area is isolated using adhesive tape and secured to the transformer frame. Next, on the simplest “winding machine” - a hand drill fixed in a vice, and with the transformer frame installed using a device (Fig. 2), the missing sections of its secondary winding are wound. The end of the winding wire is stripped of insulation in the same way, tinned and soldered to the corresponding terminal on the transformer frame.

After checking the integrity of the entire secondary winding with an ohmmeter, the previously removed parts of the magnetic circuit are installed in place and secured with a strip of adhesive tape along the outer contour of the transformer, and then the fracture sites are covered with Super-Moment glue. After 10...15 minutes of drying, wrap the previously removed adhesive tape around the transformer, solder it in place and check the operation of the monitor backlight.

If difficulties arise in finding the scarce thin winding wire, you can use the wire from the PC-13 relay (passport PC4.523.023...029); RES6 (RF0.452.100, RFO.452.110, RF0.452.120, RF0.452.130, RF0.452.140); RES9 (RS4.524.205).

Fig. 2

Literature

1. Sytnik M. A method for repairing the screen backlight assembly of some TFT monitors and laptop panels. - Radio, 2009, No. 10, p. 28.
2. Ferrites of EPCOS firm and products from them. - Radio, 2001, No. 11, p. 47, 48.

Author: E. Kondratiev

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