From: rob@despammer.com   
      
   On 05/03/2020 10:39, tabbypurr@gmail.com wrote:   
   > On Thursday, 5 March 2020 09:34:30 UTC, RobH  wrote:   
   >> On 05/03/2020 05:21, Jasen Betts wrote:   
   >>> On 2020-03-04, RobH  wrote:   
   >>>> I have some BC547 transistors which I want to use in a circuit, but   
   >>>> according to this:   
   >>>>   
   >>>> Hook the positive lead from the multimeter to the to the EMITTER (E) of   
   >>>> the transistor. Hook the negative meter lead to the BASE (B) of the   
   >>>> transistor. For an good NPN transistor, you should see “OL” (Over   
   >>>> Limit). If you are testing PNP transistor, the meter should show a   
   >>>> voltage drop between 0.45V and 0.9V. 4 May 2017   
   >>>   
   >>>> None of the BC547's give the those readings, as I get 0.02V on a few of   
   >>>> what I have, and not 0.45V.   
   >>>   
   >>> You must put your meter in diode-test mode, (on the fluke 77 it looks   
   >>> like that's also continuity beeper mode) it should say OL with the leads   
   >>> unconnected and 0.00V with them toucheing eaco other. then do the above   
   >>> measurements.   
   >>>   
   >>>> Are mine no good and should I bin them. I have had them for a couple of   
   >>>> years or so now, and only used 1 of them.   
   >>>   
   >>> I'm guessing operator error, they should still be good after only a few   
   >>> years.   
   >>>   
   >>   
   >>   
   >> Putting the meter in diode-test mode,it reads OL when leads are   
   >> unconnected and 0.00v when touching each other.   
   >> Then connecting the positive to the Emitter and negative lead to the   
   >> Base the meter beeps, then reads 0.666, the same reading when the   
   >> positive is connected to the collector.   
   >   
   > that means the tr is dropping 0.666v as each junction conducts. Black lead   
   is +ve on diode test so you have an npn tr behaving normally.   
   >   
   >   
   > NT   
   >   
      
   Thanks, and by accident I found that the transistor is working correctly.   
   I have put together a IR circuit with transmiter led and and photo   
   diode, using x2 transistors and a 555. I couldn't get to work until a   
   wire from the ground rail of a breadboard touched a leg of a 220ohm   
   resistor. Then, for some unknown reason, it works in reverse!!   
      
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