From: rob@despammer.com   
      
   On 05/03/2020 11:17, RobH wrote:   
   > 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!!   
   >   
   >   
   Update:   
   The circuit works correctly now, as I swapped another transistor, and   
   put in the wrong way round, Doh!   
      
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