what componet is this? - Page 1
Forum section: electronics / repair

author: djlorenz
author_rank: Contributor
timestamp: February 27, 2015, 10:42:44 pm
content: 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 Q1transistor?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!RegardsLorenzo

author: armandas
author_rank: Frequent Contributor
timestamp: February 27, 2015, 11:02:15 pm
content: Q marks transistors (BJTs, MOSFETs, etc). If you can read the code on the part, you may improve your chances of getting it identified.

author: KJDS
author_rank: Super Contributor
timestamp: February 27, 2015, 11:03:06 pm
content: Can you measure the voltage on each pin

author: djlorenz
author_rank: Contributor
timestamp: February 28, 2015, 10:11:32 am
content: Quote from: armandas on February 27, 2015, 11:02:15 pmit'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 voltagesthankslorenzo

author: wraper
author_rank: Unknown
timestamp: February 28, 2015, 10:34:31 am
content: Quote from: djlorenz on February 28, 2015, 10:11:32 amIf 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.

author: poorchava
author_rank: Super Contributor
timestamp: February 28, 2015, 11:59:44 am
content: 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.

author: djlorenz
author_rank: Contributor
timestamp: March 02, 2015, 11:12:02 am
content: well, the laser company answered and they gave me the modelBSS123, (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)cheersLorenzo

author: tautech
author_rank: Super Contributor
timestamp: March 02, 2015, 11:18:02 am
content: http://www.nxp.com/documents/data_sheet/BSS123.pdf

author: poorchava
author_rank: Super Contributor
timestamp: March 02, 2015, 03:04:46 pm
content: BSS123 is one of the most jellybean small-signal mosfets (along with 2N7002 and BS170/MMBF170).

author: djlorenz
author_rank: Contributor
timestamp: March 02, 2015, 03:27:09 pm
content: 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

author: wraper
author_rank: Unknown
timestamp: March 02, 2015, 04:51:14 pm
content: 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.

author: poorchava
author_rank: Super Contributor
timestamp: March 02, 2015, 05:05:34 pm
content: 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 - BSS123pmos - BSS84npn - BC847Bpnp - BC857Bsilicon diode - BAV99/BAV70/LL4448Schottky diode - BAT54/SS14+range of 0603 or 0805 resistors and capacitorsAll those cost like $1 / 50pcs or something

author: djlorenz
author_rank: Contributor
timestamp: March 02, 2015, 08:34:11 pm
content: looked at all my smd boards with tons of sot23 transistors but NO 702 at allare you sure about this code? where i can find smd codes of this transistors? they're not written on datasheet -.-"

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 02, 2015, 08:49:02 pm
content: Quote from: djlorenz on March 02, 2015, 08:34:11 pmhttp://www.marsport.org.uk/smd/select.htm

author: djlorenz
author_rank: Contributor
timestamp: March 02, 2015, 08:49:48 pm
content: Quote from: PA0PBZ on March 02, 2015, 08:49:02 pmyep thanks found out! unfortunarely i don't have any of themthanks for the help!!