01-02-2017, 07:43 PM
(01-02-2017, 05:11 PM)Nowhere-Man Wrote: Anyone have any thoughts on testing transistors already in circuit? According to the theory I read last week (refresher stuff), with the PNP transistor, each junction is either forward or reverse biased. One way will be the so-called "holes current" flowing towards -. The other way should be a larger current of electrons flowing to +. This description is about 1959 (that's how old my books are). On that basis, couldn't you set the meter on milliamps in series with the emitter and looks for a large current?
Basically I am a bit weak on transistors as most of my effort has been with valves. I know some people here do lots of transistor work although I assume most of it will be PNP Bipolar types.
Measuring the in circuit voltages on the transistor can sometimes reveal things, the emitter to base voltage for a germanium transistor is generally around 0.25 to 0.3 volts DC, for a silicon transistor it's normally around 0.6 to 0.7 volts DC.
Measuring transistor junction resistances in circuit can lead to a false diagnosis due to parallel resistive paths which generally exist in the circuit.
Lawrence.
