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Illustrated guide to diagnosis and repair of Chinese supply transistor

These supplies when analyzed calmly and with the help of the diagram are not as complicated to repair as many would argue repair. Note that I say. To begin, note that this basically consists of four transistors as follows :

1. The switching usually found marked V513 and reference 2SC4458S or equivalent NTE2594 whose characteristics can be noticed in the following screenshot :

2. The current limiter marked V512 , reference 2SC3807 (NTE2504) which should place the original because it is "special", note its factor gain.

3. The third transistor marked with reference 2SA1015Y (NTE290A) is the coupler and error amplifier

4. The fourth is the V553 as one 2SC1815 (NTE85) forming the discrete error detector.

That means it's the equivalent with their coworkers (potentiometer RP551, the R552, R553, R554

resistors, and VD561) the known TL431 or SExx family. Let's make a parenthesis to give good reasons, motivating him to study carefully this "discreet" supply. The first: found in many devices, not just televisions, another and most important of all. If he can understand and hopefully memorize its structure, insurance, repair IC supplies only, or you are with IC FET more, he will be much easy anymore because in them the same principle working or parameters applies. That is you have to meet the same conditions, before proceeding, note in the following picture, the location of the four transistors, bearing in mind that this can change depending on the design of the chassis.

Continuing on, we came in saying that these supplies regardless of whether or integrated transistor must meet the same basic conditions. One of the conditions is that voltage is present at the collector of transistor switch, because this ensures that the AC outlet, the switch (if any), the input fuse, bridge rectifier and main flattening filter are functioning properly. Also the +B, has been through the transformer primary Chopper.

If this voltage is not present, you must inspect the components corresponding to the AC part (before and after the bridge rectifier), in this diagram rectifier diode VD503 to VD506. Not to mention the R502, fuse, switch if any, the cable itself and to the same outlet or extension. Ah! And if the TV suffered an electric shock to the copper tracks that

sometimes rise or melt leaving only a trace of smoke or flash. Although this sounds very elementary, maybe not for others. Even you must recognize that sometimes overconfidence overlook these details, and after a while of looking because there is presence of AC, we found the absence of the head of evaporated copper as barely noticeable.

So with the help of this diagram and following the green arrows that you have added, according to this diagram, this

Involved: the fuse (F501), L501 (Shock shaping filter to not leave or enter interference) and R502 of 1 ohm to 7W mainly. In this condition the supply is ready to work, but you need to get started?

Starting from the supply :

I have pointed out the resistors R520 and R522 (In some supplies I found the R521 series with the R520, both of

120K). These two resistors are responsible for "Start Up". Especially the start R520 of 100K, is the cause when its value is altered or opened, the supply does not start, because obviously, is carrying the power to the circuit and starts switching when being energized. The aim is to activate the V513 to close the circuit and accumulate energy in the primary winding of the Chopper when the V513 is interrupted by V512, and so that energy transfer to the secondary.