Sony XR-55X90J 4 Blink LD Board Fix
How to Fix Sony XR-55X90J 4 Blink Error — Learn how to solve this fault. This issue is usually caused by the LD board. A red light on the LD board blinks 3 times as an error indication. When the TV is powered on, the display appears normally at first. But as the set goes into the boot loop, the backlight turns off, and the LD board starts its red light blinking sequence. As mentioned earlier, this red light blinks three times. So how did we fix this fault? In this article, we will explain the complete step-by-step solution.
XR-55X90J 4 Blink Fault Analysis
When this Sony model came to my workshop for repair, I first analyzed the fault. The customer was repeatedly asking me to check the backlight, but I prefer diagnosing the issue in my own way. After opening the back cover of the set, I started observing the fault behavior. When I powered on the TV, it showed the Sony logo normally, then shifted into a 4-blink red light error. At the same time, the LD board (backlight driver board) started giving a 3-blink red LED indication.
XR-55X90J LD Board Testing
Now I started testing the LD board with full attention. It is a complete digital backlight control system, and its detailed image is provided below for better understanding of this fault. In this board, two ICs provide the negative supply to the backlight, and a microcontroller drives both of these ICs. The microcontroller used here is STM32F401, which is based on ARM architecture. This system communicates with the main board on the I2C clock and data principle. At this point, my focus was to trace the BL error line and find the exact fault point.
LD Board Signal Testing & Fault Verification
This unit came to my workshop for the first time with this fault, so I had to put in extra effort and do proper research on it. I started by checking the LED board test point signals using an oscilloscope to understand the actual behavior of the circuit. A detailed image of this fault analysis is also attached below for better reference.
During diagnosis, I carefully observed the signals and kept the testing process slow and accurate. I also connected the negative output points of the LED board together to cross-check the response, but the fault was still present, which confirmed that the issue was not on the output side.
Complete PDF Preview File Zoom and Scroll
Sony XR-55X90J 4 Blink Fault Fix
To fix the Sony XR-55X90J 4 Blink fault, I disconnected the test point V-sync near the CN1000 connector of the ribbon cable coming from the system board. After that, I grounded the main board side of this line. This point was actually linked with the BL error detection circuit.
Once this connection was isolated and grounded properly, the fault was cleared. After the repair, I tested the TV thoroughly in different conditions to confirm stability, and the issue was completely resolved.
For better understanding, a detailed image of the LD board microcontroller IC and the section where the red LED was showing a 3-time blink indication is also attached below. This helps to clearly identify the exact fault area on the board.
Video shows the fault symptom only.
Conclusion
In this article, the Sony XR-55X90J 4 Blink error was resolved by addressing the BL error line on the LED board. A lot of effort and detailed research was put into this fault to reach the final solution. We have also included detailed images and references in this article so technicians can easily understand the fault path and diagnosis process.
Sony LED TV Repair Center Lahore will continue sharing more practical fault-finding guides like this. If you have any questions, feel free to leave a comment.
FAQ
Q1: What does 4 blinks mean on a Sony XR–55X90J TV?
A: This error is related to the LD board.
Q:2 How do I diagnose the 4 blink error on Sony XR–55X90J (LED driver board issue)?
A: Yes, this error is caused by the LD board in this model. Please read our article in detail for the solution.
Q3: Can I fix the 4 blink error on Sony XR–55X90J myself? What steps do I need?
A: No, this is quite a complex issue, you should consult a good technician or service center.
sony-klv-40W652D-sound-is-muted
Sony KLV-46BX450 6 blink error solution
KLV-40R352C No Display Panel Fix
V580DK2 Panel Side COF Data Details with Scalar Strip
BD9423EFV IC PDF Pinout & Diagram
Shaukat Ali has over 30 years of experience in LED TV repair, specializing in chip-level repair work. He is an expert in Sony LED TVs, and also repairs other major brands like Samsung, TCL, Orient, and Haier. His expertise includes display panel faults, motherboard issues, power supply circuits, T-Con, and HDMI faults. Based in Lahore, he shares real-time fault finding cases from daily repair work to help technicians and learners with practical experience.
📞 Contact: +92 321 4066054