How to Fix a Sony KDL-75W850C TV That Won't Turn On and Flashes Red Six Times?

It sounds like your Sony KDL-75W850C is experiencing a recurring issue with the T-Con board, especially since you mentioned the red flashing light. This typically indicates a problem with that specific component, which is responsible for distributing power throughout the TV. To troubleshoot further, you can start by disconnecting the cable from both the main board and the T-Con board. If the error persists after doing this, it’s likely that the T-Con board needs to be replaced. Testing the T-Con board itself can be tricky without the right tools, but if you have access to a multimeter, you can check for power going to it. If you decide to replace the T-Con board, you should be able to find one online for around $70 to $80. Alternatively, you can take the board to a local technician for testing, which might give you a clearer idea of whether it’s the source of the problem. Since you've discovered that you need a main or motherboard for your TV, I recommend checking with a Sony authorized dealer. You can order the part through their website, which should have the necessary options for your model. Just make sure to have your model number handy when you place the order. If you have any other questions or need further assistance, feel free to reach out!