Test Transistors with Multimeter and Semiconductor Analyzer

This article includes step-by-step tests on a variety of transistors:

  • NPN
  • PNP
  • Matched pair transistors
  • Complimentary transistor pairs
  • Signal vs switching transistors
  • Silicon
  • Germanium
  • Darlington
  • Devices with unexpected pinouts according to the datasheet
  • Special tools for handling SMD devices
  • Power transistors with and without shunt resistors and damper diodes
  • Known good
  • Known bad
  • Leaky
  • Unknown TO-92 part
  • 70-year-old pre-production junction transistor
  • Devices with unexpected DMM or semiconductor analyzer results

The two figures below show the various types of transistors tested in this article. Most of the package styles shown in the figure below (left) help verify pinouts for emitter (E), collector (C), and base (B). But TO-92 packages are not standardized. Refer to the datasheet/manufacturer for TO-92 devices. Even then a DMM or Analyzer test should be used to verify pin-outs from a new batch of devices. See BC517 tests below for an example where DMM test was required because the manufacturer’s datasheet was not correct for my part.

Table of Contents

DMM and Semiconductor Analyzer Test Methodology

I present a detailed test methodology for 14 different BJT transistors in this article. Here I summarize my lessons learned during this process.

  • There are four basic tests required for transistors in practical troubleshooting: gain, leakage, breakdown, and switching time.
  • Place DMM into diode check mode so enough current can be supplied to transistor legs under test for forward voltage junction readings. This will confirm whether the device is NPN or PNP.
  • The DMM ohmmeter may be used instead of the diode mode. But some ohm scales may give unexpected results. Specifically, if the ohmmeter’s test voltage is below ~650mV (for silicon) and ~300mV for germanium then forward bias issues will result. Your meter might read OL for a good device. While some devices in this article require the DMM’s ohm scales for testing builtin base−emitter shunt resistors: TIP147 and NTE89
  • For unknown devices determine forward voltage readings between one common pin (base) and the emitter/collector pins (junctions). If the base is positive then the device is NPN, otherwise, it is PNP.
  • The BJT emitter region is more heavily doped than the collector. As a result, the emitter-base junction will have a slightly greater forward voltage drop (using the DMM diode check function) than the collector-base junction. Yet one device presented in this article violates this rule: M1752
  • Orient the transistor in a consistent manner when testing each pin with a DMM. Consistency can be a big help while keeping track of device emitter, collector, base, pins 1 to 3, and positive/negative DMM cables.
  • Use the part’s datasheet where possible, but use your DMM to verify pinouts. One device in this article used an alternate pinout with respect to the datasheet: BC517
  • A semiconductor analyzer offers a range of parameters not available to a DMM.
    • Yet, a semiconductor analyzer is not foolproof either. See the discussion related to the NTE89 Power Transistor in this article.
  • SMD transistor devices offer a unique challenge based on their small size. I present tools to help test these devices in this article: MMBT5551 NPN SOT-23, PTZ2222a NPN SOT-223, and NST45010MW6T1G PNP Matched Pair SOT-363.
  • There are several options to test the hFE (DC current gain or β) parameter:
    • Use a semiconductor analyzer as shown in this article
    • Use the built-in test socket available on some low-cost DMMs
    • Parts commonly available (breadboard, two resistors, and 9-volt power source) can be used with transistor under test along with DMM to calculate hFE: see my related article Testing Transistor DC Gain (hFE) in My Lab
    • See the “Test Transistor Gain” sections within each transistor tested below for go-no-go gain tests using a DMM

Small Signal vs Small Switching Transistors

Small Switching Transistors

Switching transistors tend to have a lower DC gain (hFE) value from 10 to 200. They also tend to have a wider range of collector current IC ratings which range from 10 mA to 1000 mA. Older switching transistors likely will include their turn on TON (28 ns for 2N3638) and turn off TOFF (78 ns for 2N3638) times in their datasheet. While newer parts will have a switching characteristics section in their datasheet such as the 2N3906 general purpose transistor (TON 65 ns and TOFF 300 ns). Some datasheets don’t include TON and TOFF. Instead, they would have td (delay time) and tr (rise time) where TON = td + tr. Similarly, instead of TOFF the device datasheet would list ts (storage time) and tr (fall time) where TOFF = ts + tr. See Lecture-10: BJT Switching Characteristics, Small Signal Model for details.

Small Signal Amplifier Transistors

Amplifier transistors have a DC gain (hFE) value from 10 to 500. Their collector’s current IC rating ranges from 80 mA to 600 mA. These transistors will include a small-signal characteristics section in their datasheet, such as the 2N3906 general purpose transistor.

Test TO-92 Silicon Transistors

Test 2N3906 PNP Transistor with Known Pin-out

Click the image to view PDF Datasheet for silicon PNP 2N3906 transistor

Test 2N3906 VBE forward biased voltage drop.

Probe base (negative lead) to the emitter (positive lead) using the DMM’s diode mode.

Test 2N3906 VBE forward biased voltage drop

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

Fluke 289 DMM diode mode result

VBE test result indicates a transistor made of silicon.

Test 2N3906 transistor go/no-go gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test 2N3906 transistor go/no-go gain
Fluke 289 DMM diode mode result

DMM reading will be noticeably lower than VBE test result above.

Test 2N3906 VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using DMM’s diode mode.

Test 2N3906 VCB forward biased voltage drop
Fluke 289 DMM diode mode result

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.

Test 2N3906 VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test 2n3906 VEC for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading in diode test mode should display OL; i.e., the transistor has no leakage between emitter and collector.

Test 2N3906 VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test 2N3906 VCE for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading in diode test mode should display OL; i.e., the transistor has no leakage between collector and emitter.

Verify 2N3906 DMM Tests using Atlas DCA Pro Semiconductor Analyzer.

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N3906

Click the image to enlarge
Click the image to enlarge

Test 2N3904 TO-92 NPN Silicon Transistor

Click the image to view the PDF datasheet for silicon NPN 2N3904 transistor

Test 2N3904 VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test 2N3904 VBE forward biased voltage drop

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

Fluke 289 DMM diode mode result

VBE test result indicates a transistor made of silicon.

Test 2N3904 transistor go/no-go gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test 2N3904 transistor go/no-go gain
Fluke 289 DMM diode mode result

DMM reading will be noticeably lower than the VBE test result above.

Test 2N3904 VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test 2N3904 VCB forward biased voltage drop
Fluke 289 DMM diode mode result

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on collector and base.

Test 2N3904 VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test 2N3904 VEC for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading in diode test mode should display OL; i.e., the transistor has no leakage between emitter and collector.

Test 2N3904 VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test 2N3904 VCE for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading in diode test mode should display OL; i.e., the transistor has no leakage between collector and emitter.

Verify 2N3904 DMM Tests using Atlas DCA Pro Semiconductor Analyzer.

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N3904

Click the image to enlarge
Click the image to enlarge

Test Known Bad 2N3904 Transistor using DMM

Refer to testing a known good 2N3904 above to compare typical DMM values for VBE, VBE gain test, and VCB.

Test bad 2N3904 VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

Test bad 2N3904 VBE forward biased voltage drop
Fluke 289 DMM diode mode result

The test result shows a short between base and emitter.

Test bad 2N3904 transistor go/no-go gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test bad 2N3904 transistor go/no-go gain
Fluke 289 DMM diode mode result

DMM reading has not changed. Indicating there is no gain available with this transistor.

Test bad 2N3904 VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test bad 2N3904 VCB forward biased voltage drop
Fluke 289 DMM diode mode result

The test result is too low. Another indication of a bad transistor.

Verify bad 2N3904 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 test for bad 2N3904 transistor showing base to emitter shorted. The empty box is shown in the figure below right on purpose as there are no results to plot there.

Test BC517 TO-92 Silicon NPN Darlington Transistor

Click the image to view the PDF datasheet for the silicon NPN Darlington BC517 transistor. Note that the datasheet pin-outs for Emitter and Collector are reversed for my specific device. Don’t assume the datasheet pinout will be correct for your device.
DCA Pro shows that the datasheet pin-out for this BC517 part has the Emitter and Collector pins reversed.

In this example, the small-signal Darlington part datasheet shows the emitter (E) and collector (C) pins in reverse compared to the actual device under test here. Don’t trust the datasheet. The DMM tests are presented here to verify the pinouts.

Test BC517 VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test BC517 VBE forward biased voltage drop
Fluke 289 DMM diode mode result

VBE test results in the 1 to 1.5 VDC range indicate the transistor is made of silicon and has two emitter junctions in series.

Test BC517 transistor go/no-go gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test BC517 transistor go/no-go gain
Fluke 289 DMM diode mode result

DMM reading will be slightly lower than the VBE test result above.

Test BC517 VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test BC517 VCB forward biased voltage drop
Fluke 289 DMM diode mode result

Like most Darlington transistors, the collector terminal is laced with a resistor to limit the flow of current. So VCB test results will be much lower than the VBE value.

Test BC517 VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test BC517 VEC for leakage
Fluke 289 DMM diode mode result

For a good transistor, the VEC DMM reading should be OL indicating no leakage.

Test BC517 VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test BC517 VCE for leakage
Fluke 289 DMM diode mode result

For a good transistor, the VCE DMM reading should be OL indicating no leakage.

Verify BC517 DMM Tests using Atlas DCA Pro Semiconductor Analyzer.

By default, the DCA Pro automatically sets Ib from 0.0 uA to 0.0 uA to generate 5 traces because of the very high hFE gain for this Darlington transistor. This setup results in 5 curves all on the Ic = 0 as flat overlapping lines.
As a workaround (as shown below), change the Ib parameters from 0.0 uA for the start, and to 0.1 uA for the end, to get 5 traces looking like a typical set of curves (lower right figure). The actual Ib values for the 5 traces: 0.02, 0.04, .06, .08, .1 *

I note also the interesting and noisy results with one of the Darlingtons (BC517). That’s purely because the gain is so high that it is extremely difficult to control the tiny base currents to obtain a suitable curve. The base current control is getting close to the minimum resolution possible and therefore the graph becomes noisy.

* See the reply from Jeremy Siddons at the end of the post for more details.
Click the image to enlarge
Click the image to enlarge

Test Unknown TO-92 Transistor Using DMM

Unknown part with pins numbered for test reference

Label the three leads of the transistor with the numbers 1, 2, and 3.

Record the DMM diode readings for each permutation (order is important) of the three pins taken 2 at a time.

If the transistor is good there will be 2 tests with VDC readings from the 6 permutations that will indicate:

  • VBE forward voltage drop
  • VCB reverse voltage drop that is slightly lower than VBE

DMM Diode Mode test results for each pin combination for the unknown part.

  • Pins 1(+) to 2(-): 0.6845 VDC
  • Pins 2(+) to 1(-): OL
  • Pins 1(+) to 3(-): OL
  • Pins 3(+) to 1(-): OL
  • Pins 2(+) to 3(-): OL
  • Pins 3(+) to 2(-): 0.6805 VDC

The conclusion from the list of test values above:

  • Pin 2 is the base because this pin is common to both tests with a voltage reading.
  • Pin 1 is the emitter because pin-1-to-base has the higher voltage drop (VBE).
  • Pin 3 is the collector because pin-3-to-base has a lower voltage drop (VCB).
  • The transistor is a PNP type because the base must be negative to cause the current to flow through the emitter and collector. NPN transistors would have a base that is a positive voltage.
  • Transistor is made from silicon because the VBE VCBand voltage drops are in the range of 0.5 and 1.0 VDC. Germanium transistors would have lower voltage drops in the range of 0.2 and 0.3 VDC. Darlington transistors would have a higher voltage drop in the 1.0 to 1.5 VDC range.

Additional notes on testing an unknown transistor:

In some cases, there may be more pin combinations with a voltage reading (not just two as in the test results shown in this case). The cause may be based on a good device with internal resistor/diode components as demonstrated in some of the transistors tested in this post. A bad device may show a voltage reading on other pins as well. Also consider voltage differences for Ge, Si, and Darlington designs. And of course, the three-pin device may not even be a BJT transistor such as a FET, unijunction transistor, or something else.

Verify Unknown Part using Atlas DCA Pro Semiconductor Analyzer.

Confirmation of pin assignments and semiconductor material for the unknown transistor.

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for unknown the PNP silicon transistor.

Convert the unknown transistor data into a manufacturer part number.

Newark (among others) offers a BJT selection guide located here: https://www.newark.com/c/semiconductors-discretes/transistors/bipolar-transistors/single-bipolar-junction-transistors-bjt

Use the selections offered by Newark with the data gathered on the unknown transistor:

  • Initially, there are 3,484 parts found (at the time when this post was created)
  • Select “Suitable for New Designs”: 3,413 parts found
  • Select “PNP”: 1,354 parts found
  • Select “TO-92 Case Style”: 44 parts found
  • Select “100 hFE DC Current Gain” used here as just a ballpark value: 7 parts found
  • Of the 7 parts found for my needs, I would select: 2N3906
Click the image to see all 7 results from the Newark part search as a PDF

Now the unknown part has a proposed manufacturer’s part name for use in new designs or as a repair replacement.

Test SMD Silicon Transistors

Test MMBT5551 SOT-23 NPN Silicon Transistor

Click image to view PDF datasheet for SOT-23 MMBT5551 (incl. 2N5551) transistor

Prepare the tiny SMD TO-23 package for testing. I used this nearly foolproof spring-loaded test adapter model PCA23 by PEAK Electronics Design Ltd for easy connectivity to my DMM.

Note: I wrote the pin assignments (B for the base, E for the emitter, and C for the collector) on the adapter since the SOT23 form factor is mostly standardized – unlike TO-92 transistors.

Test MMBT5551 VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test MMBT5551 VBE forward biased voltage drop

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

Fluke 289 DMM diode mode result

VBE test result indicates a transistor made of silicon.

Test MMBT5551 transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test MMBT5551 transistor gain
Fluke 289 DMM diode mode result

DMM reading will be noticeably lower than the VBE test result above.

Test MMBT5551 VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test VCB forward biased voltage drop
Fluke 289 DMM diode mode result

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.

Test MMBT5551 VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test VEC for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading should be OL indicating no leakage.

Test MMBT5551 VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

Test VCE for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading should be OL indicating no leakage.

Verify MMBT5551 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for MMBT5551 (incl. 2N5551) Transistor.

Click the image to enlarge
Click the image to enlarge

Test PTZ2222a SOT-223 NPN Silicon Transistor

Click image to view PDF datasheet for SOT-223 silicon PTZ2222a (incl. 2N2222a) transistor

I used SMD tweezer test leads to perform these tests. They are inexpensive and fit most any DMM.

Test PTZ2222a VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test PTZ2222a VBE forward biased voltage drop
Fluke 289 DMM diode mode result

VBE test results in the .5 to 1 VDC range indicates transistor made of silicon.

Test PTZ2222a transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

Test PTZ2222a transistor gain
Fluke 289 DMM diode mode result

DMM reading will be noticeably lower than the VBE test result above.

Test PTZ2222a VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test PTZ2222a VCB forward biased voltage drop
Fluke 289 DMM diode mode result

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.

Test PTZ2222a VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test PTZ2222a VEC for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading should be OL indicating no leakage.

Test PTZ2222a VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test PTZ2222a VCE for leakage
Fluke 289 DMM diode mode result

For a good transistor, the DMM reading should be OL for no leakage.

Verify PTZ2222a DMM Tests using Atlas DCA Pro Semiconductor Analyzer.

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for PTZ2222a (incl. 2N2222a) transistor.

Click the image to enlarge
Click the image to enlarge

Test NST45010MW6T1G SOT-363 PNP Dual Matched Silicon Transistors

Click image to view PDF datasheet for SOT-363 silicon NST45010MW6T1G transistor

Prepare the tiny SMD TO-363 package for testing. I used a SOT363 DIP Breakout Board from Dreyer Electronics (purchased from Amazon).

Test SMD SOT-323 NST45010MW6T1G dual matched transistor pair using Atlas DCA Pro Semiconductor Analyzer

Device Initial TestCurve Trace: Ic vs Vce
Q1 and Q2 traces are superimposed. Note how closely they match.

Test TO-18 / TO-5 Silicon / Germanium Transistors

Test 2N2369 TO-18 NPN Silicon Transistor

Click image to view PDF datasheet for NPN silicon 2N2369 transistor
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

VBE test result indicates a transistor made of silicon.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL for no leakage.
Test working TO-18 NPN silicon transistor with known pinouts

Verify 2N2369 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N2369

Test 2N388 TO-5 NPN Germanium Transistor

Click image to view PDF data parameters for germanium NPN 2N388 transistor
This old RCA part can still be working and used in a circuit if tested first.
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

Test result in the .2 VDC range indicates transistor made of germanium.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test working TO-5 NPN germanium transistor with known pinouts

Verify 2N388 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N388

Test Leaky 2N388 NPN Germanium Transistor using DMM

Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test result in the .2 VDC range indicates transistor made of germanium.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

The test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test excessively leaky TO-5 NPN germanium transistor with known pinouts

Verify excessively leaky 2N388 DMM tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for excessively leaky 2N388. The curves never flatten as a result of the large IC leakage.

Test 2N414 TO-5 PNP Germanium Transistor

Click image to view PDF datasheet for germanium PNP 2N414 transistor
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (negative lead) to the emitter (positive lead) using DMM’s diode mode.

Test result in the .2 VDC range indicates transistor made of germanium.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using the DMM’s diode mode.

The test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test working TO-5 PNP germanium transistor with known pinouts

Verify 2N414 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N414

Test Pre-Production / Antique Transistor

Test M1752 NPN Prototype (1951) Junction Germanium Transistor

Presented here is an antique pre-production M1752 germanium junction transistor that is 70 years old as of the publishing of this article. A modern 2N3904 transistor is shown for comparison. Click on the “PDF Data on Envelope” link above to view the data supplied on the original envelope used to package the M1752 – part of the history around this transistor.

This device made history in 1951 with the press release “GORDON TEAL GROWS LARGE SINGLE CRYSTALS OF GERMANIUM AND WORKS WITH MORGAN SPARKS TO FABRICATE AN N-P-N JUNCTION TRANSISTOR.” Together with this press release, a limited number of development models of the Bell Telephone Labs M1752 were made for preliminary study in several possible circuit applications. Biophysics Lab is lucky enough to have acquired one from eBay, sourced by the Southwest Museum of Engineering Communications and Computation (http://www.smecc.org/). Also see the link in FAQ section at the end of this article: The K.D. Smith Collection By Ed Sharpe.

Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (negative lead) to the emitter (positive lead) using the DMM’s diode mode.

Test result in the .2 VDC range indicates transistor made of germanium.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using DMM’s diode mode.

For modern BJT’s test results should be slightly lower than the VBE value. Yet for preproduction devices the VCB is in fact higher than VBE. See Figure 16-2 p. 130 in “Analog Circuit Design” by Jim Williams where he points out that early junction transistors had emitter junction larger than the collector. Modern transistors reversed the size of E and C junctions where the collector is larger. See Figure 16-3 p.131 in the same book.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode. Take care not to short the thin flexible leads during the test.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using the DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test antique 70-year-old germanium pre-production junction transistor with known pinouts

Verify M1752 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for M1752

Test TO-3 / TO-66 Silicon Power Transistors

Test 2SB554 TO-3 Silicon PNP Transistor

Click image to view PDF datasheet for silicon PNP 2SB544 transistor
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (negative lead) to the emitter (positive lead) using the DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

VBE test result indicates a transistor made of silicon.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using the DMM’s diode mode.

Test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test working TO-3 PNP 2SB554 power silicon transistor with known pinouts

Verify 2SB554 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2SB554

Test 2SD424 TO-3 Silicon NPN Power Transistor

Click image to view PDF datasheet for silicon NPN 2SD424 transistor
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

VBE test result indicates a transistor made of silicon.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

The test result should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector. In this case, the difference is so small you may have to refer to the datasheet or semiconductor analyzer to be sure.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL for no leakage.
Test working TO-3 NPN 2SD424 power silicon transistor with known pinouts

Verify 2SD424 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2SD424

Compare NPN 2SD424 with PNP 2SB554 Complimentary Pair Transistors using Atlas DCA Pro Semiconductor Analyzer

See individual tests for each transistor 2SD424 and 2SB554 above.

Test TIP147 TO-220 Silicon PNP Darlington Power Transistor

Click image to view PDF datasheet for silicon PNP TIP147 transistor

The resistors are there to limit the gain at low currents and to reduce the chance of thermal runaway. The diode is there to limit transients and noise.

Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to the emitter (negative lead) using DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates transistor made of silicon.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than the VBE test result above.
Test VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using DMM’s diode mode.

The test results should be slightly lower than the VBE value. The lower reading verifies probes are on base and collector.
Parasitic diode test.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

TiP147 parasitic silicon diode is working. Vf (forward voltage drop) is in the .5 to 1V range.
Shunt resistors test.

Probe base (positive lead) to the emitter (negative lead) using DMM’s KOhms mode. Note: the DMM continues to read lower KOhm values over time.

TIP147 shunt resistors are working on this device. The ohms reading is similar to that described in the schematic.
Test working TO-218 PNP Darlington power silicon transistor that includes a parasitic diode and two performance-enhancing resistors with known pinouts

Verify TIP147 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for TIP147. DCA Pro does not provide enough current to accurately test hFE or to complete all curves

Test NTE89 TO-3 Silicon NPN Power Transistor

Click image to view PDF Datasheet for silicon NPN NTE98 power transistor

Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (positive lead) to emitter (negative lead) using DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates a typical transistor made of silicon. But this transistor is unique with extra diode and resistor so we will use .05 VDC and the normal value. Perhaps higher current than my DMM’s diode mode is required to test this transistor accurately.

VBE test only proves that transistor is NPN.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading should be noticeably lower than VBE test result above. But again this transistor shows about the same reading as VBE above. Perhaps higher current than my DMM’s diode mode is required to test this transistor accurately.
Test VCB forward biased voltage drop.

Probe base (positive lead) to the collector (negative lead) using DMM’s diode mode.

The test results should be slightly lower than the VBE value. This transistor seems to be showing a typical result for an NPN transistor.
Parasitic diode test.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

TiP98 parasitic silicon diode is working. Vf (forward voltage drop) is in the .5 to 1V range.
Shunt resistors test.

Probe base (negative lead) to the emitter (positive lead) using DMM’s Ohms mode. The test produces similar results even if the polarity of test leads is reversed.

An NTE98 shunt resistor is working for this device. The result is consistent with the schematic.
Test working TO-3 NPN silicon power transistor that includes a parasitic diode and one performance-enhancing resistor with known pinouts

Verify NTE89 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro produce test and I /V curve trace for NTE98 that look like a double diode structure in error. DCA Pro is outside the test range needed for this transistor. Yet these results may be used to identify and test other NTE98 transistors using the DCA Pro.

Test TO-105 / TO-106 Silicon Transistors

Test 2n3638 TO-105 PNP Silicon Transistor

Click image to view PDF datasheet for silicon PNP 2N3638 transistor
Test SetupLab PhotoDMM Test Result
Test VBE forward biased voltage drop.

Probe base (negative lead) to the emitter (positive lead) using DMM’s diode mode.

Test result in the .5 to 1 VDC range indicates transistor made of silicon.

VBE test result indicates a transistor made of silicon.
Test transistor gain.

Short collector to base using the same probe setup as above for measuring VBE (above).

DMM reading will be noticeably lower than VBE test result above.
Test VCB forward biased voltage drop.

Probe base (negative lead) to the collector (positive lead) using DMM’s diode mode.

Test result should be slightly lower than VBE value. The lower reading verifies probes are on base and collector. This part has increased readings over time so care must be taken to measure VBE and VBC with the same amount of “on” time.
Test VEC for leakage.

Probe emitter (positive lead) to the collector (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL indicating no leakage.
Test VCE for leakage.

Probe collector (positive lead) to the emitter (negative lead) using DMM’s diode mode.

For a good transistor, the DMM reading should be OL no leakage.
Test working TO-92 PNP 2N3638 silicon transistor with known pinouts

Verify 2N3638 DMM Tests using Atlas DCA Pro Semiconductor Analyzer

Results from DCA Pro model DCA75 Test and Ic /Vce Curve Trace for 2N3638

References

Hardware
Atlas DCA Pro Semiconductor Analyzerhttps://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html
PCA23 – Peak Component Adapter for SOT-23 SMD Transistors (there are other ways to probe a loose SOT-23 device but this seems to be the easiest)https://www.peakelec.co.uk/cgi-bin/sh000001.pl?WD=pca23&PN=pca23-peak-component-adapter-sot23%2Ehtml
Pomona Electronics – 5143-K-48 – SMD Tweezerhttps://www.pomonaelectronics.com/products/dmm-test-leads-and-probes/smd-test-tweezers-banana-plugs
Fluke 289 True-RMS Data Logging Multimeter with FlukeView forms and IR/USB cable (although any DMM with a Diode mode will work)https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-289-fvf-kit
PanaVise Model: 201  Jr. with Model: 239 Speed Control Handlehttps://www.panavise.com/index.html?pageID=1&page=full&–eqskudatarq=1
My lab’s support for SMD devices
My lab tools for SMD soldering
FAQs
Test a transistor with a multimeterhttps://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07
Semiconductor device numbering/coding schemeshttps://www.electronics-notes.com/articles/electronic_components/transistor/transistor-codes-numbering.php
The K.D. Smith Collection By Ed Sharpe (Many references to the M-1752 junction transistor)https://www.smecc.org/the_k_d__smith_collection_by_ed_sharpe.htm
Books
The Transistor Experiment; how to calculate hFE using breadboard; pp 87-90 and Fig 3-19; Chapter 3All New Electronics Self-Teaching Guide, Third Edition; H. Kybett and E. Boysen; Wiley; 2008https://www.academia.edu/30599085/All_New_Electronics_Self_Teaching_Guide_Third_Edition
Building Blocks for the Linear IC Designer; Chapter 16; A. Paul Brokaw; Junction Transistors (such as M1752) and Improved Junction Transistors (modern day); Figure 16-2 & Figure 16-3 pp. 128-131Analog Circuit Design, Art, Science, and Personalities; Edited by Jim Williams; Elsevier; 1991https://doc.xdevs.com/doc/_Books/Jim_Williams_The_Art_and_Science_of_Analog_Circuit_Design.pdf

1 Reply to “Test Transistors with Multimeter and Semiconductor Analyzer”

  1. Your work here is amazing, I’m really interested in all your results!

    Thank you so much for putting all that time into the testwork.

    On the subject of the M1752, it looks like the Vceo of the device means that it is starting to breakdown as the Vce is getting bigger. This causes an avalanche and therefore the Vce actually drops even though the voltage across the load and the transistor is increasing.

    I note also the interesting and noisy results with one of the darlingtons (BC517). That’s purely because the gain is so high that it is extremely difficult to control the tiny base currents to obtain a suitable curve. The base current control is getting close to the minimum resolution possible and therefore the graph becomes noisy. Very interesting.

    Thanks once again for your brilliant evaluation.

    If you have any questions at all then don’t hesitate to let me know and I’ll be delighted to assist you and your readers.

    Kind regards from us here in the UK,

    Jeremy Siddons
    Engineer and Managing Director
    Peak Electronic Design Limited
    Atlas House, 2 Kiln Lane,
    Harpur Hill Business Park,
    Buxton, Derbyshire,
    SK17 9JL, UK.

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