Identification of SMD transistor

Dear all,

I recently got two identical PCB's which are used for an aroma diffuser. One PCB works and the other doesn't. I took a closer look into the PCB's and noticed that the one which isn't working has a missing transistor, which is present in the other board, and the code in the package states as "RO" or "R0".

Is there any way I can look for the part with this information?

Regards!

Codes like that are manufacturer specific and very cryptic. Do you know what it does? That should give a clue as to what it is and its current rating. It could be a FET or a BJT or even two diodes.

MarkT:
Codes like that are manufacturer specific and very cryptic. Do you know what it does? That should give a clue as to what it is and its current rating. It could be a FET or a BJT or even two diodes.

I have no idea... But as I do have one PCB with the part I guess I could test it somehow to figure something out. What would you recommend me to do?

post photos of both sides of the pcb?

Unless you have some test equipment, such a volt Ohmmeter, aDVM, and an oscilloscope, there is not much hope in even identifying the function of the device.

When the good board is in operation, measure the voltage on each of the three pins to ground. Then look at the signal on each of the three pins with an oscilloscope to "see" the signals. Then you will have a chance of at least classifying the device.

Paul

MarkT:
post photos of both sides of the pcb?

Paul_KD7HB:
Unless you have some test equipment, such a volt Ohmmeter, aDVM, and an oscilloscope, there is not much hope in even identifying the function of the device.

When the good board is in operation, measure the voltage on each of the three pins to ground. Then look at the signal on each of the three pins with an oscilloscope to "see" the signals. Then you will have a chance of at least classifying the device.

Paul

I only have a multimeter, and followed this guide which states that the method only works for PNP and NPN transistors. The results were not satisfactory, so, I guess the transistor I need is not a simple PNP or NPN type.

Regards

Remember you test is while the device is "in circuit" while the guide is for a device all by itself. What are the results you got fro the test?

Paul

Paul_KD7HB:
Remember you test is while the device is "in circuit" while the guide is for a device all by itself. What are the results you got fro the test?

Paul

You are totally right. I will desolder the device and repeat the test. Thank you!

I desoldered the device, soldered again to a PCB adapter, and repeated the test.

This are the results:

Hmm, not sure about that device, possible damaged BJT. The photo isn't clear enough to follow all the traces alas. The device may be involved in setting output current levels or something like that. Do F+/F- and Y+/Y- go to some sort of motor?

Does the device involve any radio-frequency (RF) function?

I located a device with that marking: the KTC3879 ("0.05A , 35V, NPN Plastic Encapsulated Transistor".)

If it is, you might try an MMBT3904 in its place.

Unfortunately, the silkscreen font on your part suggests Made In China and so the supply chain is probably also strictly Asia so being sure of a match is tricky. Can you trace out where each of the pins go?

Perhaps here

The problem is.... R0 or RO (I wish this font had slashed zero's) is not unique. There is no standard or universal registration so there are other devices with the same marking on the market.

Google SMD marking code and you will see the other possibilities.

BRI0:
I took a closer look into the PCB's and noticed that the one which isn't working has a missing transistor, which is present in the other board, and the code in the package states as "RO" or "R0".

What I notice is that the transistor you circle appears to be blistered.

I would have a sneaking suspicion that on both PCBs, the transistor has been seriously overloaded and on one, it overheated and simply melted its solder connections and fell off!

What you need for testing these SMD devices conveniently is a very clever gadget called an Ardutester! Very clever device and convenient to use to test all sorts of things.

MarkT:
Hmm, not sure about that device, possible damaged BJT. The photo isn't clear enough to follow all the traces alas. The device may be involved in setting output current levels or something like that. Do F+/F- and Y+/Y- go to some sort of motor?

F+/F- are connected to a Fan, and Y+/Y- are connected to a ceramic disc.

I followed all the traces involved for the F+/F- and Y+/Y- resulting in the following :

1 Like

Q2 and Q3 form a push pull driver of the base (gate?) of the NPN (N-channel) Q5.

Edit: the measured voltages are neither a bare BJT nor a MOSFET. Maybe it could be a Darlington or a J-FET?

Edit2: You did desolder Q5 from the working or damaged board?

Paul__B:
What I notice is that the transistor you circle appears to be blistered.

I would have a sneaking suspicion that on both PCBs, the transistor has been seriously overloaded and on one, it overheated and simply melted its solder connections and fell off!

What you need for testing these SMD devices conveniently is a very clever gadget called an Ardutester! Very clever device and convenient to use to test all sorts of things.

Thank you very much for the advice! I will definitely get one of those testers.

Smajdalf:
Q2 and Q3 form a push pull driver of the base (gate?) of the NPN (N-channel) Q5.

Edit: the measured voltages are neither a bare BJT nor a MOSFET. Maybe it could be a Darlington or a J-FET?

Edit2: You did desolder Q5 from the working or damaged board?

I desoldered Q5 from the working board, the other board is missing that piece.

Regards.