Page 125 - Testing Electronic Components

2. If two low readings are found for one connection of the black probe
(test no 1 & 2), while each of the other two position gives two high
readings (test no 3, 4, 5 & 6), then the transistor is NPN type.

3. The pin where the black probe is connected to showed two low
reading when the red probes connected to the other two leads shows
high reading is the “Base”. In the above case pin 1 is the “base”.

Your test probe placement must be reversed in order to check for PNP
type of transistor as shown in Figure 3.

∞ ohm 0 Test Red probe is Black probe Reading in
No connected is connected ohms
to pin no to pin no
1 1 2 Low

2 1 3 Low
3 2 1 High (∞)

4 2 3 High (∞)
- x1 Ω + 5 3 1 High (∞)

Black probe Red probe 6 3 2 High (∞)

1 2 3
Figure 3 : Identifying a PNP Type of Transistor and pin leads

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