Electronic – how does a transistor behave when it’s broken


I'm trying to get a circuit to work (linistepper driver) and I suspect I may have fried the drive transistors (tip122's in this case).

Are there common behaviors of broken transistors?

does c->e short? b->e? open?

Can I measure with my multimeter to get any meaningful information?

is it possible for devices to half break with degraded performance?

I'm looking for generalities. I also have an old stereo which has a broken channel.

I'm not particularly good at desoldering, so it'd be good to have some confidence that I'm looking at the right component.

Best Answer

In my experience, power transistors fail shorted. All the pins will measure low resistance to each other.

TIP122 is in TO-220 case. All three leads are in a row, at least in the linistepper. The way to desolder this part is to add solder until all three joints are bridged in a big solder blob. Melt the blob, then pull the part out. Then clean the solder blob up with a solder sucker, then braid. Do not attempt to desolder one pin at a time.