DIY samsung 940n monitor repair

Today I will tell you how to repair an inverter with your own hands.

If your monitor has a defect that it turns off after two to three seconds after being turned on, and at the same time the image appears at the time of turning on.

A trance defect can be determined by a device for short-circuited loops, by resistance.

Usually one of the trances breaks. This is, in principle, a disease of monitors.

The simplest option, in the absence of a trance, is to install a new inverter, of which there are many on sale.

A detailed examination revealed a defect in one of the inverter trances. It is easy to check this: you need to try the working candle one by one, first at the exit of the first trance, then the second, and so on alternately. In a non-working trance, the candle will naturally not light up at the moment of switching on.

Without going into details, we solder the transformer of the TMS91429CT inverter so that the protection does not work.

After dismantling the trance, it will look like this:

Then we take a ready-made inverter, for the same number of candles (4 candles), which are freely sold on radio markets, radio stores, etc., such as: model SF - 04S402, dimensions: 135-45 mm. Or something similar, the main thing is to fit the inverter in size.

Next, we supply it with power and control, place it with Velcro in a convenient place. It may be necessary to increase the length of the wires from the lamps to the output of the inverter.

Here are some examples of inverter placement.

And here are examples of ready-made inverters.

It will not be difficult for a person to disassemble.

I got the Samsung 940N monitor on the occasion. When turned on, an image appeared for a second, then the screen went out. During verification, a faulty backlight transformer was found (breakage of one secondary winding). There was no new transformer, and its replacement in workshops was slightly less than the cost of the monitor. It was decided to try to restore it at home.
The transformer was removed from the monitor board and inspected. Its design could not be disassembled. Since the converter for the backlight lamps was single-ended (there is most likely a gap in the core of the transformer), it was decided to carefully break it in order to try to restore it in the future (gaps during gluing should not greatly impair its operation).

Video (click to play).

With a screwdriver, its side jumpers were carefully broken off from the W-shaped core. Then, to free access to the winding, the plastic frame of the transformer.
The old winding was cut off and a new one was wound in its place, 8 sections of 80-100 turns in one section with a thin wire (it was 0.1), preferably even thinner is needed.

After winding the winding, the transformer core was glued with super glue. The photo shows the glued seam. The frame of the transformer was also glued together. It turned out without the upper protective part (the pieces were too small).

Below in the figure is a view of the transformer from the reverse side, the new winding is on the left side, the terminals are not yet soldered. After soldering the leads and dialing the transformer, the resistance of the new winding turned out to be much lower than the remaining one. Well, this is understandable, the new winding was wound with a wire thicker than the original one.

Next, the transformer was installed in the monitor power supply board (new winding on the underside of the board). The monitor was assembled and performance tested.
After turning on the monitor, all the backlight lamps lit up, the power supply did not go into protection. Test run of the monitor showed quite satisfactory operation of the repaired transformer.

It is also possible to restore the performance of the monitor without rewinding the transformer - by transferring the monitor to work only from 2 backlight lamps (one on top and one on the bottom), which can be powered from the remaining working secondary winding of the high-voltage transformer.To do this, it will be necessary to remove the SMD diode "CA2": D10 or D11 from the monitor's power supply board (depending on which transformer winding is faulty) and rearrange the backlight lamp connectors accordingly. The faulty winding will need to be mechanically, carefully removed (cut with a knife). After that, accordingly, the brightness of the monitor will decrease slightly, but the monitor will remain quite working.

They brought 2 samsung monitors for repair - 940n and 740n. Most often, these devices have problems with the power supply, but, interestingly, there are several modifications of these same units for the forties models. Our guys got one modification for both seventeen and nineteen inch models. Accordingly, we will describe the repair of this modification here.

The first thing to do is to look at the display from different angles (preferably with the D-SUB cable disconnected, which VGA goes to the video card). If it is noticeable that the inscription “cable not connected“Then this is our patient. The backlight does not work for the patient, and everything else is normal.

Of course, in order to fix this beast, it must be disassembled. This is done quite simply - we remove the leg and half the body. I half the body using this blue piece that looks like a pick (photo below). You can buy it in most radio markets and one such thing costs about 15 rubles. It is not suitable for any technique, but for both monics, one such was enough for me.