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| panoss:
Following measurements are all in DMM 's Diode Mode. C-E(Negative lead to C, positive to E): 0.027. E-C:(Negative lead to E, positive to C): 0.033. I measured a 30 Ohm resistor (as I don't have a 27 Ohm resistor, even with combinations) : 0.027. |
| WattsThat:
Those are not not resistance values, they are voltage values as the meter is displaying the voltage drop of the device’s PN junction. You check both forward and reverse biased directions, forward bias with red probe on P (anode), black on N (cathode) show proper voltage drop for the material type, 0.6-0.7 volts for silicon, 0.2-0.3 volts for germanium. When you reverse the probes and reverse bias the part, the meter should show INF with no current flowing. When you see a very low voltage in both the forward and reverse directions, like you identified on the failed transistor, it is because the charge junction between the P and N sections has been destroyed and it is shorted/fused together. |
| panoss:
--- Quote from: WattsThat on April 12, 2020, 05:19:42 pm ---When you see a very low voltage in both the forward and reverse directions, like you identified on the failed transistor, it is because the charge junction between the P and N sections has been destroyed and it is shorted/fused together. --- End quote --- But I did not see a very low voltage in both directions. (we 're always talking about diode mode measurement) As I mentioned in reply #123, 'in diode mode it looks fine'. So the transistor looked fine when I measured it in diode mode, this is why I was thinking it 's ok. It was proved to be damaged only when I measured it in resistor measurement mode after Xavier 's suggestion. |
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