Panasonic PT-51HX42F turns on, no picture and led light blinks three times

The convergence circuit has shut down. You can get the convergence repair kit for your model at www.tvrepairworld.com the kit contains the parts and the CD with instructions.

Your symptom sounds like a damaged convergence IC.

This is a common failure for this particular television. The power light is blinking indicate a short in the power supply,

There are two and large IC’s that control the convergence in a big screen set. Some of the newer sets only have one. They are secured to a very large aluminum heat sink. They will have a part number stamped on them that will start with an STKXXX-XXX, like STK392-110, and they are located on the signal board (on the left as you look into the back of the set).

Along with the convergence IC’s there will also be some associated components that will need to be replaced as well. There are some resistors that are part of the convergence circuit that will be open and need to be replaced. Most likely these will appear charred in the center. If you have an Ohm Meter or a DVM, check all the resistors that are close to the IC’s and you should be looking for either ones that have opened or have changed values.
There are also two resistors on the front of the board located in the middle that are fusible link resistors, these should be checked for opens and replaced if they are found so.

If one of the convergence IC’s are found to be bad, I would replace them both, if one has gone bad the other may go soon. I usually order my parts from Andrews Electronics in California, they will have the OEM components that you will need.
Their site is http://www.andrewselectronics.com/welcome.aspx
And their phone number is a 24-Hour Order Desk: (800) 274-4666
I recommend the phone order so you can talk to the person about the different types of IC’s that are available.

I would also advise that the convergence IC’s be OEM or better, just because they are cheap does not mean that they are a good deal. I have seen the cheap IC’s fail after a short time, even though they look exactly like the OEM IC’s. I think that the bottom line is that you will get what you pay for when it comes to the parts.

You can also try http://www.tvrepairkits.com/ , I have not tried them yet, but they do carry OEM or better parts.

I hope this information allows you to resolve this issue.
If you need further assistance please comment to this post and I will try to help you further.
asnowman