I repeated above breakdown voltage tests on my new S8050 Bipolar NPN transistor with both my perfect working DY294 Testers to make sure they both were working fine and are giving the same results which they did!
So it must have been a bad transistor pincontact that previously lead to not reaching the correct breakdown voltage on the 200V and the 1000 (over 1600V!) testscales.
Now I got even better results than those given in the datasheets (depending on the manufacturer the voltages are often not the same) and I got normal acceptable values!.
So as in the manual is written just use only the E and C connections on your DY294 Meter/Tester to test the BREAKDOWN voltage of any Diode/Triode, and connect in case of a NPN triode like my 8050:
1. For the Vcbo (collector-base) breakdown voltage test, simply connect the Collector of the transistor to the C connection on the DY294, and the Base of the transistor to the E connection of the DY294.
2. For the Vebo (emitter-base) breakdown voltage test, connect the Base to the E connection of the DY294, and the Emitter to the C connection of the DY294.
3. For the Vceo (emitter-collector) breakdown voltage test, put the Emitter on the E connection and the Collector to the C connection of your DY294.
And press the test button on the 200V or 1000V scale selections to read the breakdown voltage on the display. The breakdown voltage normally kills any semiconductor but in our DY294 its is a protected voltage test which doesn't destroy your transistor/diode (or capacitor)! But never touch any wires of contacts while pressing the test button!
In case of a PNP transistor you need to reverse the Base and Emittor transistor connections because the current (the arrow in the emitter symbol) flows in the other direction.
There is also a 4th Breakdown Vces test but that is only a Vceo test with the base connected the the emitter.
My DY294 testers gave a Vcbo of 81V (30,40 or 45V depending on what manufacturer), a Vebo of 11V (5, or 6V depending on the manufacturer), and a Veco voltage of 26V (25V in most datasheets).
So everything works as is to be expected! Problem solved.

And we only have to be careful when we are using the current tests. If we only use these tests for a very brief moment, our semiconductors won't be harmed! Something that probably was not mentioned in the user manual.

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That is true, Parasuraman! The more experienced that I get the more that I appreciate having Mr. Yong's e-books, and the more that his teaching is validated.

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Albert. I noticed that also with the DY294 on one of those other settings and burned my fingers. I checked the transistor just like the manual says. Now I only use the DY294 for checking insulation and zeners only. I use my other insulation tester for capacitors because it will discharge them automatically.
I am going to check all diodes, transistors, FET's, etc. with my VOM first from now on. And when it fails one I will check to see if my DCA75 Pro passes it.

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Robert, I noticed something very odd about testing the CBO and EBO max breakdown voltages with our DY294 Tester. I was unable to determine the breakdown voltage of my in a Corsair VX450W repair used S8050 NPN transistor.

Maybe it is something that can be explained? Because strangely both the CBO and the EBO voltages exceeded any of the in the datasheet given maximum voltages. Although I in my new soon to be published repair wrote that the higher CBO was about 60V and the lower EBO only about 25V, my DY294 showed in both tests about the max 1630V DC but my DY294 display began flickering while I was pressing the test button longer down.

The CEO voltage my DY294 gave was splendidly 26V as given in the datasheets.

I also tested the Iceo which was 1574uA on the 2000uA scale test. (IMPORTANT!: many DY294 users are unaware that these I ampere current tests can destroy the weaker diodes instantly because they get hot without even having to press the test button during these selected current tests.)
And to make sure my transistor wasn't destroyed after the tests, I tested the NPN in my other digital testers which showed a perfect working NPN with a Hfe of 293 and a Uf of 629mV.

I have no idea what is the correct explanation behind these very high breakdown CBO and EBO voltages of the S8050 NPN under test? (other transistors are giving a decent breakdown voltage!).

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The DAC is not a sure shot and has proved wrong in my experience. Analogue millimeter in X1 range and recheck on X10 is sure to expose the defect. If the reading between B to C and B to E, is not identical, just replace the transistor. Our expert, Jestine Yong also strongly recommends use of Analogue Multimeter.

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That's good to know, Albert. I know that the DCA75 Pro has it's limits but mine hasn't been wrong yet on transistors. It was wrong on some diodes. I will keep an eye on it.
Just goes to show that we can never trust anything 100% of the time. It's always good to have many meters and not to depend on just one meter.

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Hi Albert. Yep, sometimes transistors test good with most testers but fail when they are put under a load. The good thing about the VOM(with X10K) is that it can find the culprits and it is also not very expensive. Nearly anyone in the world should be able to afford one.

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Thanks for the valuable tips Parasuraman! It wasn't a secundary coil in the transformer or anything like that but a transistor that previously tested as a good NPN transistor on my DCA75, but still was out of spec. I managed to find the culprit after rechecking and yesterday made a new repair about my finally solved not working Fan problem that was almost untraceble until I compared it with the component datasheet and desoldered the components again for a confirming second test!

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The coils in the secondary are very important. If we read Jestine yong's world famous book on SMPS Repair, he has covered how important it is to replace the coil, if necessary. I did it once in an SMPS, as it was found blackened. Even salvaged, good looking one will do. Did you check the switching pattern in an oscilloscope? You might already know that connecting the ground of oscilloscope to Hot ground and just keeping the probe on top of the SMPS will give us a good swing. Watch whether it varies or stays stable. If it varies, the problem is in the primary section. Similarly, you can connect the scope to secondary too and check. Not on Transformer, but on the circuit.

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Robert, I finally found the culprit! The Fan is working now! A previously 'working' transistor unexpected turned into a diode. I will make a new repair article about it.

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