Transistor: NPN; bipolar; Darlington; 100V; 5A; 65W; TO220AB
#TIP122
Darlington NPN 100V 5A 3-Pin (3+Tab) TO-220AB transistor in TO-220 package.
To see if your transistor is bad, use a digital multimeter set to the diode check mode.
(-) = negative/black test lead
(+) = positive/red test lead.
Pin 1 = the pin with a dot above it.
For TIP122s, these are typical voltage drop values when measured with a typical multimeter in diode test mode.
When replacing TIP122 transistors, verify that the diode on the coil in question is not shorted, or the replacement will fail.