Identifying SMD Component

Discussion in 'The Projects Forum' started by xmtg2o7, Mar 20, 2016.

  1. xmtg2o7

    Thread Starter New Member

    Mar 20, 2016
    Hi guys,

    I'm working on diagnosing and repairing a double din touchscreen radio. I can't find any schematics for the LCD circuit board so I've been reduced to guesswork. I've identified what I believe to be the problem but I would like a more experienced opinion.

    The main problem is that the radio LCD screen turns off immediately after being turned on. Other components still show they are getting voltage and the cooling fan will still turn on after the unit warms up. I hooked it up to an AC to DC unit in my house and tested the circuitry. After playing with it for a while I believe I have found one of the problems. The unit will power off when started at 12v but I can get the LCD panel to stay on when it's set just below 10v. I traced the voltage issue to a spike shown below. When the radio recieves 12v it steps it down to 10.6v to a lot of the components on the LCD board. There appears to be a transistor that steps that voltage back up which leads to the cathodes in the LCD piece. The problem is that at 12v in it steps up the voltage from 10.6v to 30v. When I reduce the input voltage to 10v it now recieves 7.8v and steps it up to 18v which will power the screen without it shutting off. The problem there is that now some other components aren't working and the radio is still useless.



    So my question is does this sound like a likely problem or is this just causation from another possible problem with the unit? My next question is did I identify this SMD component correctly in thinking that it's a transistor? My last question is how would I go about replacing it if it were the culprit (finding a replacement, I'm comfortable in soldering on a new one).

  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    In the first picture, the left item with 000 is a 0 ohm "resistor." In other words, a jumper or bridge.
    The other item has a marked end suggesting it might be a diode or polarized capacitor. Since the screen print starts with a "D". I suspect it is a diode.

  3. xmtg2o7

    Thread Starter New Member

    Mar 20, 2016
    You are absolutely right. I managed to get a schematic of the board and it is a diode. It is supposed to up the voltage to about 27v so it appears that the diode is not the problem and I am back to square 1. Thanks for your help.
  4. SLK001

    Active Member

    Nov 29, 2011
    When an LCD screen comes on briefly, then shuts down, the problem a lot of the times is in the display area (specifically, the backlight). How is this display lighted? If it is CCFL, then check for a bad bulb. I suspect CCFL because of the higher voltages.