How to Fix Sony KLV-40S400A No Display Problem – Fault in T-Con Board VGH missing
I have an LCD TV, Sony model number KLV-40S400A, to be repaired in the workshop. The customer told me that there was no picture in it. I switched on the TV and saw that the picture was indeed not showing and there was sound. It was an old model Sony. My customers were also quite old. So my first impression about this TV was that the problem was with its panel. Its panel has a separate T-CON board, and I thought that there must be something wrong with it due to which this panel is not showing a picture. So I told the customer to leave it. I will check it and diagnose its fault and then contact you. The customer said, OK, keep it, and I will fix it.
Physical inspection
First of all, I opened this TV in my workshop and started its physical inspection because it is an old model, so there was a lot of dust in it. I cleaned it and checked the power supply of the main board, and after that some of its appearance came out. I saw in its main board that its HDMI ports were also not working because its parts were damaged. During the checking, I thought that they must not be working, and when I asked the customer about it, he said that yes, they do not work; you will fix them too, but the main fault was obviously that there was no picture. I removed the cover that is on top of the T-CON and inspected the T-CON. Apparently, I did not see any problem in it.
VGH Missing – Fault Fixed
Now I started checking the voltage of this T-con; its 12 volts were present, 17 volts, which are for AVDD, were also present, and the minus voltage, which we call VGL, was also present, so when I checked its VGH voltage, they were not present. This was its real fault: when the VGH voltage does not come, the picture will not be formed. I started checking its resistance, and then I found a register with the DC to DC IC whose value was 150K, which was faulty, so I replaced this faulty register, and then VGH voltage started to be generated. As soon as this voltage was generated, the screen turned on, and my screen fault was fixed.
HDMI Port Repair – Faulty Zero Ohm Array Resistors
Now the next step was to repair its HDMI ports, so since this is an old set, it is not surprising that the HDMI ports do not work because there are coils attached to the HDMI port. Since these are old and large sets, these coils do not get damaged. These coils are fine. Behind them, there are resistors in series, which are zero-ohm resistances. They were damaged. I changed those resistors. These are in the form of array resistors. was damaged, and some of them were damaged. Anyway, I changed all of them. By installing new resistors, my HDMI port issue was fixed. One of my pots could not work in it because there was a lot of rust in the socket, so I left it like that, so in this way, the HDMI issue of this set was also fixed.
- 🔧 Repair Summary
- Started checking voltages on the T-Con board
- 12V supply was present
- 17V AVDD voltage was also present
- Negative voltage (VGL) was present as well
- VGH voltage was missing, which is essential for image display
- Suspected issue near the DC to DC IC on the T-Con board
- Found a faulty 150KΩ resistor next to the IC
- Replaced the faulty resistor with a new one
- After replacement, VGH voltage started to generate
- As soon as VGH appeared, the screen turned on
- The no display issue was successfully resolved
- HDMI Port Repair – Faulty Zero Ohm Array Resistors
HDMI Port Repair – Faulty Zero Ohm Array Resistors
In this case, you saw that there was a fault in the Sony LCD TV, no display, that it was not giving a picture, so the main fault was this and how we removed it, it was the fault of the T-CON, we did not change the T-CON card, we repaired the card, the job of a good technician is to save money, do the best job at the least cost, so one of the problems was that of the display, we solved it, the 150 ohm resistor in its T-CON was faulty, we changed that resistor, so the display issue was fixed, but along with that, its HDMI ports were also faulty, we repaired them, their zero-signal array resistance was faulty, they changed it, so the HDMI started working properly, so in this way we repaired an old model Sony TV.
Q1: It is often seen that older model Sony LCD TVs have display issues. Why is this?
A1: Older Sony models use separate T-CON cards, so it’s no surprise that they have some faults due to their long lifespan, as they are quite old. This is a common fault.
A2: Since we are talking about a very old television, meaning 12 or 15 years old, it is also their lifespan, so they may have faults depending on their lifespan.
A3: There are also other display-related faults, for example, a short circuit within the panel or damage to the COFs.
“To read another repair article on Sony KLV-40W652D not turning on, click here for the complete troubleshooting guide.”
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Shaukat Ali
Shaukat Ali is a professional Sony LED TV repair technician with over 30 years of experience. He specializes in diagnosing and fixing complex display and board-level faults. Based in Lahore, he shares real-world repair cases to help both customers and fellow technicians.
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