Unplug the TV and remove the diode by de-soldering the diode's leads.
Locate the single band on one end of the diode. The band indicates the cathode (negative) end of the diode.
Connect the black (negative) multimeter lead to the COM input jack of the multimeter. Connect the red (positive) multimeter lead to the volt-ohm-milliampere input jack of the multimeter.
Attach the red multimeter lead to the positive (anode) lead of the diode. Attach the black multimeter lead to the negative (cathode) lead of the diode.
Turn the digital multimeter selector knob to its lowest ohmic setting and read the display. Reverse the multimeter lead connections to the diode, and read the display. Compare the values. If the first reading is relatively low and the second reading relatively high, then the diode tests good. If the first and second readings are both low, this indicates that the diode is short-circuited and will allow current flow in both directions. If the first and second readings are both high, then this indicates that the diode is blown with an open circuit that will not allow current flow in either direction.