what componet is this?

[djlorenz]

hi guys!
trying to repair my DPSS laser that has broken modulation... it has a switch between analog and TTL modulation that was in short...
tried to remove the switch but it's not, it's this component behind him that has two pin shorted... any idea of what it can be? it's marked Q1

transistor?
looks like one pin is connected to ouput and one to - of an OP AMP (741C), so looks like in the feedback...
i don't care about switch, i only need it in one position (i use only analog modulation)
if anyone can help me really appreciated!

Regards
Lorenzo

[armandas]

Q marks transistors (BJTs, MOSFETs, etc). If you can read the code on the part, you may improve your chances of getting it identified.

[KJDS]

Can you measure the voltage on each pin

[djlorenz]

Q marks transistors (BJTs, MOSFETs, etc). If you can read the code on the part, you may improve your chances of getting it identified.

it's impossible to read on that... too little and also damaged... the only thing i can recognize is something like SA or AS on it..
i'll re-try today with sunlight...

and i'll also measure voltages

thanks
lorenzo

[wraper]

Q marks transistors (BJTs, MOSFETs, etc). If you can read the code on the part, you may improve your chances of getting it identified.

it's impossible to read on that... too little and also damaged... the only thing i can recognize is something like SA or AS on it..
i'll re-try today with sunlight...

and i'll also measure voltages

thanks
lorenzo

If you cannot read that, get magnifying glass. Cleaning the part with alcohol or other solvent will help too. If marking is partially damaged, try to find same part on the pcb and read full marking from there.

[poorchava]

In the end you can reverse engineer this part of the circuit, infer the function of that component from its place in the circuit and then try to find something that matches the function.

My initial guess would be that it is used to change opamp gain somehow or to reset a peak detector of an envelope detector.

[djlorenz]

well, the laser company answered and they gave me the model 
BSS123, (Slice-style Transistor)

l don't think i have them at home... any idea of what it can do and if i can use other types of MOS (but i don't think i have any of them)
cheers

Lorenzo

[tautech]

http://www.nxp.com/documents/data_sheet/BSS123.pdf

[poorchava]

BSS123 is one of the most jellybean small-signal mosfets (along with 2N7002 and BS170/MMBF170).

[djlorenz]

so is it changeable wirh 2N7002 and BS170/MMBF170? i'll have a look what i have home... i don't think i have any smd component... probably i'll buy them from RS components... they're really cheap... is the shipping costs the problem

[wraper]

If you have some old dead PC motherboard, very likely you will find sot-23 with 702 marking which is 2n7002. Should work instead of this.

[poorchava]

In general something like this should be amongst collection of components everyone doing electronics-related stuff should have at home. There was even a thread about it some time ago.
Personally:
nmos - BSS123
pmos - BSS84
npn - BC847B
pnp - BC857B
silicon diode - BAV99/BAV70/LL4448
Schottky diode - BAT54/SS14
+range of 0603 or 0805 resistors and capacitors
All those cost like $1 / 50pcs or something

[djlorenz]

looked at all my smd boards with tons of sot23 transistors but NO 702 at all
are you sure about this code? where i can find smd codes of this transistors? they're not written on datasheet -.-"

[PA0PBZ]

where i can find smd codes of this transistors?

http://www.marsport.org.uk/smd/select.htm

[djlorenz]

where i can find smd codes of this transistors?

http://www.marsport.org.uk/smd/select.htm

yep thanks found out! unfortunarely i don't have any of them
thanks for the help!!