Help with SMD

[lavo-1]

I'm trying to fault find on a Humidity controlled extractor fan circuit that has gone faulty in my bathroom.
I have tested all the through hole components and even replaced the OP amp just in case.
The problem is there are six SMD components on the board that I don't recognise and to be honest haven't a clue how to test as I don't know what they are.
They are I believe, SOT-23 packages as I measured their dimensions. They all have three pins/legs.
They have Identity codes of:

A4,
L2 Z2,
LN Y4.



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I'm sure you guys that work regularly with SMD components will recognise the numbers.

[Psi]

They can be quite hard to figure out, but you might get some ideas from

http://elektronik.googlecode.com/files/SMD_Catalog222.pdf
http://www.s-manuals.com/smd/


A component tester really helps for this, as you can easily check if its a transistor, fet or diode and narrow down the possibilities.

[vtl]

Maybe post a picture. Component location can sometimes give you clues to what it is

[Psi]

yeah, and the silkscreen text as well.

[lavo-1]

I've popped some pics in to help

[Zero999]

I think you need to provide more information.

You say it's faulty, how? What does the fan remain on continuously? Does it fail to start? Or does it randomly turn on and off?

Have you tested the fan? and the humidity sensor?

Your pictures are a bit too small to see and you've loaded them to imageshack which I find inconvenient - it's better to upload them here if you can and there's no reason not to if they're under the 1000KB limit.

[lavo-1]

Sorry if the images are too small.
The Fan is running continuous once activated. I have checked the Humidity sensor with a DMM and a kettle and its fine. I have checked all the resistors (smd and through hole) and checked the two smoothing caps.
I rigged up a Triac latching test using an led circuit and a 9v PSU which was fine as it latched on both + and -
I just am not sure on the three legged SMD's as I am not sure what they are. I suspect that they maybe a bunch of Diodes and a FET, but I'm not 100%.