Panasonic plasma tv model:TH-42PV8AZ no power found Q406 rjk5020 short and f401 and 402 8a fuse short,please help what can i do cannot find Q402 RJK5020 can you give me a substitute number to use or whats the remedy.

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The main power regulator board will have some shorted component/s on it. Normally, these boards to plasma TVs are irreparable. Card base replacement should be done.

If TV is completely dead you have either a bad power or a bad main board.

Talking form experience I'd go with the power board first.

The alternative is to make sure the power board outputs the normal standby power to the main board and see that the main is not responding to command. That would point to the main.

The fact that Q406 is not shorted does not mean it is good let alone that the power board is good; while the most common issue there it is definitely not the only one that can happen.

You can send in the board for inspection/repair if interested although you're probably better off just buying a replacement.

You have a power supply issue. You will need to replace the power mosfet Q406 and likely one or both of the 8 Amp ceramic fuses. The Mosfet is under a heat sink which will also need to be removed. It doesn't hurt to double check the rectifier diodes while you have the heat sink out of the wqay. They are probably fine though. There are also two 10 ohm fused resistors. They are the two small white ceramic boxes R410 and R413. One of these may be open as well.
Parts can be found on ebay.

I think its better swap the the boards.

This is a dead short, check power supply for diodes bad or zeners

When this happened it probably took out Q406 a switching field effect transistor on the power supply board along with F401 an 8 amp Slow Blow fuse. The FET will have to be soldered in if it is bad. If the fuse is blackened, it is almost certain that the FET is shorted as well.

Go to newark electronics on line.

replace fuse 8 amp and Q406 part number RJK5020 both on the power supply board

On a Panasonic TV the 10-blink error code can sometimes be caused by low voltage running through an HDMI cable, particularly from a Media PC or some video game consoles. Try disconnecting any HDMI cables and unplugging the Television for 30 seconds, then power it on without the cables attached.

If this works, connect the cables to the front panel (usually HDMI-3) which uses a different controller board.