Testing BJT transistors for shorts or opens.
The majority of "Bad" transistors are due to shorted junctions. This is my attempt to simplify the routine for those that may not already know the process.
Photo 1
Transistor lead identification - If this is unknown you will need to find a spec sheet on the transistor under test.Sometimes it is provided on the schematics " legend" or even silkscreened on the printed circuit board.
Photos 2 & 3
Testing the Base-Collector Junction***With your DMM in the Diode Check function -Attach test leads as shown.One direction should show -OL(open) - and in the other direction a similiar value to the one depicted in the photo ,depending on whether its a PNP or NPN determines the direction of conduction.
Photos 4 & 5
Testing the Emitter-Collector Junction*** As seen in photo. Both directions should show (open) in a good transistor reguardless of NPN or PNP.
Photos 6 & 7
Testing the Emitter-Base Junction*** Again depending on NPN or PNP. One direction will show (open) and the other direction a similiar value to the example depicted in the photo.
NOTE:The transistor in the photo is a " serviceable " example. ONsemi MJL4302A PNP
If your meter at any time - beeps continuously - and/or reads a low value close to zero . First verify your test leads are not touching.If they are not touching ---You have identified a faulty junction and a unserviceable transistor.
Good luck..I hope this is helpful..
Dave
The majority of "Bad" transistors are due to shorted junctions. This is my attempt to simplify the routine for those that may not already know the process.
Photo 1
Transistor lead identification - If this is unknown you will need to find a spec sheet on the transistor under test.Sometimes it is provided on the schematics " legend" or even silkscreened on the printed circuit board.
Photos 2 & 3
Testing the Base-Collector Junction***With your DMM in the Diode Check function -Attach test leads as shown.One direction should show -OL(open) - and in the other direction a similiar value to the one depicted in the photo ,depending on whether its a PNP or NPN determines the direction of conduction.
Photos 4 & 5
Testing the Emitter-Collector Junction*** As seen in photo. Both directions should show (open) in a good transistor reguardless of NPN or PNP.
Photos 6 & 7
Testing the Emitter-Base Junction*** Again depending on NPN or PNP. One direction will show (open) and the other direction a similiar value to the example depicted in the photo.
NOTE:The transistor in the photo is a " serviceable " example. ONsemi MJL4302A PNP
If your meter at any time - beeps continuously - and/or reads a low value close to zero . First verify your test leads are not touching.If they are not touching ---You have identified a faulty junction and a unserviceable transistor.
Good luck..I hope this is helpful..
Dave