# can anyone identify the fried transistor?

#### strantor

Joined Oct 3, 2010
5,591
My friend brought me this remote control. He said the LED doesn't work. Looks like he's gone in with a soldering iron fried the crap out of the transistor that switches the LED. why he was in there with a soldering iron?; don't know. is/was the transistor the only problem?; don't know. what I do know is that this transistor needs to be replaced. If there ever was a part# on it, it's been burned off. I think it matches the dimensions of a to-23 package pretty well. I am pretty sure from looking at the circuit that it's a NPN, the top is the collector, right is emitter, and left is base. can anyone give me a part# for something that has a good chance of working? here's a pic:

Thanks a bunch

#### Attachments

• 93.2 KB Views: 106

#### SgtWookie

Joined Jul 17, 2007
22,221
Probably an SMT version of a 2N3904, like an MMBT3904.
http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Several years ago I was visiting my folks up north; their cordless phone had died. Found there was a dead NPN transistor that turned out to be an MMBT3904. No way to just walk in somewhere and buy one of those, but there was a Radio Shack store in town; I picked up a 15-pack of their NPN resistor assortment. They generally come with five 2N22222's, five 2N4401's, and five 2N3904's. A bit of creative lead-bending and soldering, and the phone was back in working order.

At least, until my dear Dad dropped the phone in his soup bowl...

#### R!f@@

Joined Apr 2, 2009
9,749
Hey dummy...show me a clear pic and I can tell for sure..

#### strantor

Joined Oct 3, 2010
5,591
Probably an SMT version of a 2N3904, like an MMBT3904.
http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Several years ago I was visiting my folks up north; their cordless phone had died. Found there was a dead NPN transistor that turned out to be an MMBT3904. No way to just walk in somewhere and buy one of those, but there was a Radio Shack store in town; I picked up a 15-pack of their NPN resistor assortment. They generally come with five 2N22222's, five 2N4401's, and five 2N3904's. A bit of creative lead-bending and soldering, and the phone was back in working order.

At least, until my dear Dad dropped the phone in his soup bowl...
lol. thanks wookie. I'll see
Hey dummy...show me a clear pic and I can tell for sure..
hey that's the best I can do with a crappy camera phone with no focus. I tried for 5 minutes to get one that even looks that good.

#### strantor

Joined Oct 3, 2010
5,591
Cool idea bertus. It worked, but upon looking at my image I see that the transistor in question (Q1) has fallen off somewhere between my desk and the printer. It was only holding on by half a trace. I have no idea where it is, so even though it won't be of any help, here is the picture for proof of concept:

#### Attachments

• 215.2 KB Views: 89

#### debe

Joined Sep 21, 2010
1,251
Just a sugestion, we have 2nd hand stores here that have bins of old remotes for 50c-$1 ea get one & ime sure youl find a simmilar transistor in one to remove. These parts are simmilar in most remotes. #### Sparky49 Joined Jul 16, 2011 833 It also looks like the top track (and pad) has come away... #### R!f@@ Joined Apr 2, 2009 9,749 what kinda junk have u got ? Kid. #### bertus Joined Apr 5, 2008 21,452 Hello, I have changed the brightness of the picture and selected the bottom part. It is a pitty that the defective transistor already is removed and can not be seen for markings. Bertus #### Attachments • 95.2 KB Views: 71 Thread Starter #### strantor Joined Oct 3, 2010 5,591 Just a sugestion, we have 2nd hand stores here that have bins of old remotes for 50c-$1 ea get one & ime sure youl find a simmilar transistor in one to remove. These parts are simmilar in most remotes.
That's a good Idea. I'll tell my friend. I already sent him the link for the replacement so we'll see what he brings me.

It also looks like the top track (and pad) has come away...
It has. He heated it up so much that all 3 pads lifted and the trace all the way to R2 lifted.
what kinda junk have u got ? Kid.
it's remote control junk. I told him to just get a universal remote but he says he already tried that and it won't work. this is for his cheap chinese security camera DVR system.
Hello,

I have changed the brightness of the picture and selected the bottom part.

It is a pitty that the defective transistor already is removed and can not be seen for markings.

Bertus
Thanks. that looks a lot better. The picture probably still wouldn't be much help if the transistor was there; there were no markings on it, even through a high power magnifying glass. I only posted the first pic for a size reference so that maybe someone could confirm my suspicions as to the package type.

#### R!f@@

Joined Apr 2, 2009
9,749
By junk I meant, tht do u have any PCB's tht you can salvage parts from.
Basically u can get the tr from TV Pcb's.

At least I do u know

#### strantor

Joined Oct 3, 2010
5,591
By junk I meant, tht do u have any PCB's tht you can salvage parts from.
Basically u can get the tr from TV Pcb's.

At least I do u know
Ah, yeah. Actually I need to check my junk heap at home. I bet I do have that.

#### THE_RB

Joined Feb 11, 2008
5,438
They usually run up to 1amp peak currents, you need a SOT-23 tranny with 1A peak capability, I would just use a BC817 that should get you up and running.

PS. The LED is likely burnt out too!