Help with replacing diode and transistor

Discussion in 'General Electronics Chat' started by zersys, Apr 29, 2014.

  1. zersys

    Thread Starter New Member

    Apr 29, 2014
    Hello all,

    I have limited understanding of this kind of stuff, so please bear with me.

    I have an issue with a back light on an LCD monitor out of a car. I believe I've found the cause of the problem, a burnt diode and a burnt transistor (I think that's what they are anyway). Here is a photo of the suspect parts .

    I've found someone that can de-solder the old bits and solder the new bits for me, but he was unable to find the replacement parts! I think I found the correct transistor here, not sure if the 2S prefix makes it different, or the fact that on the bottom right of the part my one has "23" and the one pictured has "67" (what does this actually represent? Revision number?). Would that transistor work as a replacement?

    But I and a few other places have had no luck finding a replacement for the diode, J4S 23. The guy I spoke to who will be doing the soldering for me said that it wasn't an issue, and that he can find a similar diode that "should work". I'm a bit hesitant to just go by something that "should work".

    I found another thread here that has been the most helpful of all. From what I can gather when putting the site through a translator, this guy describes the same symptoms as my problem, he has the same two burnt parts, and he himself replaced them which fixed his problem. But he too had trouble finding J4S 23 (again, what does the 23 represent?), but in the end he said he used F2J4S, which I am having trouble finding.

    Basically, what is a suitable replacement for that diode, and will the transistor I mentioned above be suitable? I am assuming that you guys will see this information and be able to give me an answer with ease, but if my assumption is incorrect and leg work is required, could somebody guide me in to the right direction so that I can find the suitable replacement?

    Thank you.
  2. Wendy


    Mar 24, 2008
    Welcome to AAC. You triggered the sites auto-moderation because you are both a new member and had links to other sites, which looks like spam to the forum software.

    I have unmoderated your thread.
    zersys likes this.
  3. wayneh


    Sep 9, 2010
    Hmmm. Could be this, or this.

    Can you get a better close-up?

    Oh, and usually the second line of a label means nothing. Manufacturing date or some such code of no use.
    zersys likes this.
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
  5. PackratKing

    Well-Known Member

    Jul 13, 2008
    It would help to back-pedal a wee bit, and determine why the components popped in the first place...
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
    The transistor is a P-channel MOSFET - you have to add "2S" in front of what's stamped on it to google the datasheet.

    The diode could well be a Shottky-barrier type, if its toast, the only way to tell is find a schematic or an identical diode elsewhere on the board to measure its Vf.

    SB diodes have a Vf around 0.2 - 0.4V, plain old silicon are more like 0.6 - 0.65V - zener give more like the fabled 0.7V on a DMM diode check.
  7. zersys

    Thread Starter New Member

    Apr 29, 2014
    Not at the moment, the board is back in the car. I have this other photo though.

    And thanks for clearing up what the other numbers mean!

    The board is out of the 16:9 NAV head unit found in the BMW E39. The flickering backlight and eventually dead backlight is somewhat of a common issue, but not many people bother to investigate as far as I have, they just replace it with an after-market unit, but I like to keep my cars OEM.

    My best guess is that it occurs when people jump start the car incorrectly, there's a specific way to do it without frying/bricking the millions of modules in the car (in fact, the whole process is regarded as an absolute last resort because the car is so sensitive when it comes to electricity).

    I'm pretty sure that's what happened with mine because I bought the car with the problem and it had an NRMA road side assist battery in it which was not only installed incorrectly, but it wasn't the right battery for the car. The PO said he thinks it may have happened around that time, but he doesn't know if the road side assistant tried jump starting the car, but logic tells me that he would.

    Okay so the transistor is sorted for the most part, thanks for confirming that.

    As for the diode, I'll have to find an identical one on the board and also find out how to measure its vf (forward voltage, right?), which I'm sure is a really trivial task to you guys :p, but remember that I am an electronics noob.

    The schematic for this board is the first thing I searched for, and was unable to find anywhere on the web. If anybody wants to have a go at it, the model is below.


    Thanks for all the help so far guys!
  8. ian field

    AAC Fanatic!

    Oct 27, 2012
    Its quite some time since I last saw a DMM that DIDN'T have a diode check function.

    You don't need a high priced top of the range model for those odd handyman jobs - shop around, you should be able to find one pretty much pocket money prices. But make sure it has the diode check.