Do you have a type number or p/n for the transistor. I have 1000s of transistors, civilian and military types, be glad to help you out.
Paul,
It's probably not all that difficult to find a working replacement, but in a different form factor. Can you show a larger portion of the schematic? I'd like to see if this transistor is operating as an on/off switch, or if it's trying to work some magic to regulate the voltage on the magnet for fast pull in and then low current idle.
I attach the whole thing. There are explanations in the schematics.
I measure about 0 V on the base of Q1, but also about 0 V on the base of Q2. My understanding (which could be wrong) is that when one is on, the other one should be off, and vice versa, which means that 0 V on Q1 should lead to about 4.7 V on the base of Q2. In any case, I am not getting any voltage to the selector magnet through Q2 (the large transistor on the heat sink, separate from the board), which is the original problem I am having.
Some basic DC measurements might give you some insight into the health of the transistor without removing it from the circuit board.
This is what is leading me to Q1: it seems that there is continuity between emitter and collector, which I don't think there should be! I have another instance of the board where this is not the case. (However, that second board also doesn't seem to work, but there might be something else wrong with it.) I could desolder the transistor on that one and transplant it to see if that gets my first board working, but I was trying to avoid doing that immediately.
I'd be curious to know the voltage from base to emitter when the transistor is "ON" (or supposed to be on). Also (can't see that part of the schematic) but if there's a resistor in series with the base I'd be curious to know the voltage across the resistor (and the resistance of the resistor), and then use ohms law to determine the base current. Same thing for the selector magnet current, if that's possible.
-Erik
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