JTAG communication error

Hi everybody!

Recently I do a board about ep2c8,now all pins have been weld, and power is Ok! When I use USB_blaster download a test program ,quartus show me download success,but fpga doesn't work.Then I use signallTap in quartus ,download ok too,but when i run it ,it show me "Jtag communication error"

:confused:

Thanks for everybody can help me !!

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