High Speed trouble shooting advice

[DRANO]

For anyone with a similar problem... The part is a NPN 2N3904 transistor. Here is the testing procedure:

NPN TO-92 package (2N3904, 2N4401, 2N5550, 2N5551, 2N6427, MPS-A13, MPS-A42, PN2222A)

Set DMM to diode test mode.

1. Place the red lead of your DMM on the center leg of the transistor
2. Probe each of the flanking legs with the black lead
3. .4 to .6 volts is a normal reading
4. Readings outside of this range indicate a failed transistor

 

[sylvain]

Good test procedure info for an NPN transistor from Drano above.
Some transistors might read up to 0.7 volts or so in diode test, and some Darlington drive transistors down to 0.35 volt or so.
Note that the machine power must be OFF when performing such test.