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im trying to identify the following 4 transistors, but am having trouble tracking them down.

The one that I think is the dual transistor is marked .1Ft on top of it, and the other three leg one is marked 3BW and then 2b (sideways on). After a search on the internet I found these two as possible replacements : http://www.ebay.co.uk/itm/271507549901?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://www.ebay.co.uk/itm/BC856B-NXP-Transistor-PNP-Sot-23-/360843952989?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5403f9c35d

but info on these two transistors seems to be really thin on the ground. Is there a way to test the transistors and find out what the rated current etc is, as there are several of them on another board that I have that is identical and still working.

enter image description here

enter image description here

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2 Answers 2

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I guess we can actually identify those from the markings, as you can see here for 1ft and here for 3bw. The 2b seems more tricky, but take a shot here.

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Identifying SMD components is usually not possible. Markings, if present, rarely refer to what's inside the package. That is done because there is no room for useless information, and because printing them rises costs. Only "big" resistors, as 1206, are usually marked.

That said your best shot is to desolder one of the working one, find out if it's a fet or a bjt, then understand if it's a p or a n device testing it with very low voltages to avoid breaking it, then hope it's not some special very low noise, very high frequency, very whatever device, maybe having a guess at what it's doing on the board, buy a replacement and throw it in.

If there are several of them they are probably standard small signal transistors, some 100mA of collector/drain current, 100-ish hfe, 1-2V threshold voltage... But that's a wild guess.

Knowing what the board is supposed to do can help a lot.

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  • \$\begingroup\$ Thanks for that, its a battery monitor board for an ebike, it also controls the balancing and charging in between cells. \$\endgroup\$ Commented Sep 11, 2014 at 12:45
  • \$\begingroup\$ with all that silicon I think it does something else too... \$\endgroup\$ Commented Sep 11, 2014 at 12:47
  • \$\begingroup\$ There are three pcbs in the photo for three separate packs, only the central pcb is fried. \$\endgroup\$ Commented Sep 11, 2014 at 12:50
  • \$\begingroup\$ Its this thing here, there are 7 connections for 7 packs adaptto.ru/i/BMS.jpg \$\endgroup\$ Commented Sep 11, 2014 at 12:53
  • \$\begingroup\$ Just thinking....would it be possible to work out a compatible component by hooking up some wires to some of the traces of the working ones and then measuring the current / voltages when it is turned on ?. \$\endgroup\$ Commented Sep 11, 2014 at 14:17

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