SOT Markings

I can't help you with your engineering exploits but can relate to you the time I looked

at a small portable nascar scanner and noticed an obscenity printed onto a part of the board where a blob of black goop was instead of components.I can never find any markings on SOT packages either.

Some manufacturers deliberately erase the labels and print their own part numbers on them. Evidently, they don't want anyone copying their circuits.

I did decipher one circuit once. It was a disco light controller that the other technicians had given up on. I traced the circuitry and one of the IC's circuit looked distinctly familiar. It was an 8 pin DIL (dual-in-line) and had one capacitor, one resistor and a potentiometer. I immediately recognized it as a 555 circuit. It was the source for the timing pulses and from just this one start, I got the whole circuit eventually figured out. Took me a week to do that but it was a very satisfying bit of sleuthing. Finally, knowing how it worked enabled us to find the problem.

I believe you can trace this item down by googling for remote control ICs. If you can get a data sheet, you might find the circuit that you've got in your hands. It may take some time but you seem to have enough of it.

Good luck.

Ah, yes, I too have had moments of glory like that (an example of which was a "Dude, that's an LM386!" moment I had a while ago). Unfortunately, it seems we've had a miscommunication -- the part I'm looking for isn't an IC, but a SOT-23 package something. That means the "R16" I found had characters about 1/32" tall, and the "P7" was about 1/64", if that.

Anyway, maybe I'll try searching backwards -- that is, seeing if I can find SOT-23 packages that bear the markings I've seen, rather than searching for them using those markings.

I'll post how well I do using this method.

Yes, I guess I was a little too quick to get my letters in .

An SOT-23 has 3 pins but is not necessarily an ordinary transistor, if I'm not mistaken, which presents an additional problem in identification. For all I know, the R16 designation means that it's a resistor network of some sort. 'Tried measuring resistances on it?

It would appear that a SOT-23 is a surface mounted 3 leg device, so it is most likely a transistor, but could be a diode I am informed....

How about removing it from the circuit and checking its parameters out with a common multimeter that has a transistor checker, this may help you further in defining whether its PNP or NPN and its aproximate gain.

Measuring the voltages in the circuit, should give you some voltage parameters to go on....

(I am assuming that the part is still in working order!)

The following site (or others like it) might help:

http://www.tkb-4u.com/code/smdcode/

Say! That looks promising! Only problem is that zfuller mentioned in the initial post that the code was "K16" then said that the code was "R16" in post #3. I found the K16 but the R16 might actually be an R1G (I've made that mistake before).

So, which is it?

zfuller, the reason why SOT`s are marked this way is simply that they are so small that the full device name is to big to print. The reason is not to hide the real name because bigger devices are mostly readable and often worth to hide as well - if not then they are custom specific.

If you want to know the real part number of those tiny things you have to go to the manufacturers home page. They mostly have cross reference lists where you can look what these 2 or 3 character abbreviations mean.

Regards Uwe

Wow, you guys rock. Special thanks to Sharkybaba - I think I figured it out. It turns out it's an NPN-type "digital transistor" with a 47K base-emitter resistor. At least, the site's description of it is "npn dtr 50V 100mA R2 47k," so does anyone see anything wrong with my analysis?

Again, Sharkybaba, this is exactly what I was looking for! Thanks for all your help, guys! I don't think I've had a forum question answered faster or more completely.

Glad it proved useful. I once had a SOT-23 device in a circuit I was trying to work out. It seemed like it had to be a transistor but none of the options made sense. I found that web site and it identified the device as a thyristor. Everything suddenly fell into place.

By the way, I apologize, the "R16" in my third post should, in fact, be "K16". Sorry for the confusion!

Thanks,

Zach