Transistor C33725 "no gain"
I send you as an annex to everything indicated, a tester of Master Jose Miguel.- I hope it serves you, analyze it.- On the other hand I tell you.- The test with the multimeters has been useful, but not effective.- To know the beta of the transistor you would have to test it dynamically.- with simple circuits but in such a way that you can see its behavior at different voltages. regards
Of course, Josduart, but I'm also interested in learning. That is why I ask why I mark zero in profit if the transistor does not seem short, not open or leaking. Thanks for your answer.
The non-presence of gain (hfe) is one of the parameters that indicates that a transistor is damaged, for me in those cases I discard the transistor since the transistor must not always be short to consider it as defective. In the diagnosis I always use a transistor tester that gives me the hfe measurement. Regards...
Thank you very much, Josduart and Felipe Antonio. It shows when the subject is mastered. I only have two doubts to finish understanding it:
1) For Felipe Antonio: When you say that to test the transistor you have to do it dynamically, with load, does this mean that testing it in the multimeter slot, that specific for transistors (hfe), the result is not reliable?
2) For Josduart: Do you think that the non-presence of transistor gain would explain that it was very hot, so much so that it almost burned? The encapsulation is of the to92 type, without heat sink.
Thanks for your patience.
Subject to the opinion of Master Josduart, the test is inconclusive due to the low voltage referenced by the transistor under test. I send you a circuit diagram where the ratio of the base resistance is proportional to the load current and involves the beta or gain of the transistor. Here you can use it at different voltages and draw a conclusion with any transistor. greetings everyone.
If your transistor gets hot, you can do the indicated circuit and test it at the voltage you have and the current you want. You can choose the transistor beta (I have not seen the data), in this way fulfilling the requirement of the load current and the beta you can analyze the behavior of the transistor with voltage closer to the established and see if it meets the specifications. appreciate that you like the numbers. So I suggest you look for a course in applied mathematics. They are preparation courses for the oscilloscope. Regards.
Well, Felipe Antonio. I just tested the proposed circuit and the transistor responds well. With an intensity at the base of 0.5ma it offers one between collector and emitter of 120ma, putting a small bulb as a load. I have heated it with a hair dryer and the transistor does not faint, which seems to be correct. I will have to look at other surrounding components.
The strange thing is that neither of my two multimeters mark any gain in the transistor when it seems that it does generate it according to the circuit.
Thanks again and greetings.
I send you the formulas we use. .- (Ic = beta x Ib) .- (beta = Ic / Ib) .- (Ib = Ic / beta) .- (Ib = v + minus 0.7 between Rb) .- The base resistance is what the diagram has , just observe that the current between the beta, is the charging current, (collector charging) .- If you have the diagram upload a photo of the circuit, and a photo of the diagram where you are testing it, and so we can analyze. regards
You need to comment 1.- what voltage are you using from power supply to the collector.- 2 .- how much current the load consumes (relay) .- 3.- the voltage where you are going to connect the base.- 4.- and the beta that You are taking as a reference. If possible send photos and diagrams with numbers. Greetings.
I send you a diagram of a tester that we had a long time ago.- I found it in Electronic Forums. I send you another diagram, this one is more elaborate, but you can do it in your free time and connect to a digital multimeter. Regards.
Hello again, Felipe Antonio.
I am not at home to be able to test the circuit you proposed to me, but I send you a (a bit unfortunate) scheme of the test I did yesterday with the transistor. According to the datasheet, that I am trying to send as an attachment but there is no way, for a current in the collector of 100ma the gain must be between 160 of minimum and 400 of maximum.And now the funniest thing comes, and the multimeter is not I measured the gain because the transistor pins were too short and did not make contact, so I made an "extension" of the legs and managed to see a reading of 240 HFE. This data coincides exactly (too even) with the test I did, since 120ma collector intensity / 0.5ma base intensity = 240.
With all this, I only have to find an explanation for the heating of the transistor, which in my opinion seems excessive and I think that is what makes the amplifier fail. Also, as I said at the beginning, it makes me suspect that the plate is obscured just below the transistor. I have thought of putting a heatsink to the new transistor, although those of the TO92 type do not seem to need to be cooled.
I want to thank you for your explanations, they have helped me a lot to understand the subject somewhat better even if I am finally unable to repair the blessed TV amplifier and end up in the trash. As I do not want to abuse your patience more, if you have any more contribution to make, I am all ears, and if not, then I will give your comments as the best solution.
Greetings to all.
Mr. Jose.- I have a lot of patience, what I don't have is a lot of knowledge.- But it was good that he could prove it.- now for the collector voltage 12 / 15v of these 12v are used a 7805 is connected and from there it will have the voltage For the base (I will use the diagram I send), Send a photo of the TV or the diagram of the audio part. We have a tracker that feeds with 9 v cd and an oscillator with 1.5v- If you like I send you diagrams. We are (here we work 3 technicians) .- to help you in everything you need.
I send the diagram based on what you sent.- In this way you will have a meter with sufficient voltage and current for the collector and a constant and reference source for the base. Regards .
¡Aprende a reparar con estos cursos YoReparo!
Curso Reparación de Fuentes Conmutadas de PC y Equipos Electrónicos
