Sony TV KDL-40EX520 4 blink error fix

Fault Introduction

A Sony LED TV KDL-40EX520 came to my workshop with a common fault but a serious issue 4 blinking red light error. In this article, we will explain in detail why this model has a 4-blink error. We will also explain step-by-step how to troubleshoot the main board and power supply. 

Check power supply voltage

• First of all, we will start with the power supply because this error is generated due to the twelve volt line. Later, you will see which line that is. Let’s start. First, we will disconnect the power supply and check the voltage. 

Power supply switching

You have to connect the three points of the power supply together. 

Jack number CN6201

• Pin 10 stby 3.3V
• Pin 8 t-con on
• Pin 1 3.3V

By connecting these points together, you will investigate the power supply to see if its mains voltage, e.g. mains 12V, is correct.Specifically, the 12 volts of the T-con are coming out. Let’s assume that the power supply for our T-con is not coming out. In such a situation, we went to check the MOSFET of the power supply and its related components. My personal observation is that its MOSFET gets damaged. If you replace it, the four-time blink error will be solved. 

To make this easier, I’ve included a picture.

What to do if the power supply is fine?

Now let’s move on to the next step. This fault also occurs in the main board. In this case, I have identified the fault from the main board itself. The system IC needs a voltage reference so that it can know that the T-con is getting supply. So let’s move on to our next level, which is investigating the main board.

Sony TV mainboard 4 blink error

Since the main board is alive, you can hack it somewhere.You have to find the reference point on the main board that is related to the T-con VCC. I will tell you in a simple way. Connect the power supply to the main board and look at CN6201 from where the T-con supply Output is happening. Set your multimeter to buzzer and find the voltage divider resistance on the back side of the main board. The resistor on which you hear the buzzer sound and full contact is shown will be R1 and Along with this, R2 will be grounded, which will be the voltage divider to provide a reference to the system. In my case, R1 was bad.

4 blink error fault solution

Using the method given above, I found the voltage divider resistors on its main board. I removed these resistors from the circuit and checked their value with a multimeter. I found the value of R1 to have increased. I replaced this resistor 22k and my fault was fixed.

Conclusion

We have written this article about this four-blink fault step by step.

Everything has been taken care of in this, from where this fault is generated, we have also covered the power supply unit and the main board. This fault can occur in both areas in this model.If a fellow technician has any confusion in his mind, he can comment and get a satisfactory answer.