Testng RF power transistor.  - Page 1
Forum section: electronics / beginners

author: Bibigo
author_rank: Newbie
timestamp: March 16, 2021, 09:13:24 pm
content: Hello. Nice to be a part of that great community.Testing the final power amplifier RF transistor (2SC2904) on my ham radio with multi-meter.Base to emitter 0.58 V - okBase to collector 0.58 V - okEmitter to base 0 - okCollector to base 0 - okCollector to emitter 0 - okEmitter to collector 0.58 V - not ok???Does having 0.58 Emitter to collector mean the transistor is bad?

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2021, 09:31:12 pm
content: are you using the meter diode test function on it?

author: Bibigo
author_rank: Newbie
timestamp: March 16, 2021, 09:48:50 pm
content: Yes.

author: Manul
author_rank: Super Contributor
timestamp: March 16, 2021, 10:40:57 pm
content: Hello. You did not mention is it out of circuit or in circuit?

author: Bibigo
author_rank: Newbie
timestamp: March 16, 2021, 10:47:55 pm
content: It is out of circuit.

author: Manul
author_rank: Super Contributor
timestamp: March 16, 2021, 11:37:12 pm
content: To me it is suspicious, the transistor or the measurement. It looks like it contains colector-emiter reverse diode? It should not. Anyway, I would just take a pair of resistors, make a simple circuit to test hFE and see if it works.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2021, 08:25:29 am
content: When you write "0" do you mean "OL" or something?There does not exist, a stateless* component, that measures a diode drop in one direction, and 0.000 in the other.*MOSFETs can be tested in this way, by charging the gate (test G-S, reads OL) then measuring D-S or S-D (0.000 either way, if Vgs(th) is below the test voltage used). Discharging the gate (touch G-S with fingers, or test S-G to reverse bias it) returns it to normal operation (D-S open, S-D diode). Note that in this case, one would have to omit the charge and discharge steps (or accidentally perform them in this order), to measure a diode one way and 0.000 the other way. Anyway, the gate capacitance stores state, therefore this is a stateful measurement. BJT capacitances discharge much too quickly to measure the same way, so are effectively stateless.Edit: anyway, the apparent measured E-C diode doesn't seem to be in conflict with the Mitsubishi datasheet. It doesn't give an internal diagram (that might suggest a diode in that position), and the ratings it does give, do not include E-C bias. (There is Vebo of course, but this can be measured with Vc > Vb or Ve, so does not include such a diode if present.)Tim

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 17, 2021, 09:02:00 am
content: Quote from: Bibigo on March 16, 2021, 09:13:24 pmsince you don't mention the testing polarity, I cannot advisesecond, apparently your transistor doesn't have reverse protection diode for C-E junction, so in theory the transistor is bad except if you have strong RF near him when you test ita good multimeter give different voltages for B-E and C-E junctions, Vbe is slightly bigger for a normal transistorif unsure of multimeter/testing conditions, just put some resistors and polarise the thing or use some gm328 tester or whatever transistor tester you can put your hands onsooner or later, in real electronics world you'll need one