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Simple LED Circuit

By on December 22, 2010


If you need to build the simplest LED circuit then just refer to the photo or click on the photo for more information. It is easy to make the LED light up-just use a paper clip and a battery. This website was recommended by Beh.



  1. Mark Peacock

    December 22, 2010 at 6:48 pm

    Hi Jestine,

    I am working on a Dell 1800 FPK monitor. I am getting very funny readings on my Digital MM. Could you please look at these and tell me where you think the problem might be. AC current is 110 volts.

    Fuse 123.4 volts AC
    Bridge Rectifier 123.7 volts AC
    Main Filter Cap 171.9 volts DC
    VCC Pin on IC 18.7 MVolts
    First Diode 111.9 volts DC
    2nd Diode -48.9 volts DC
    Power Coupling to
    Main Board 329 volts DC on all pins

    I have check all of these reading twice.\
    Thanks for your help.
    Mark Peacock

  2. admin

    December 23, 2010 at 10:49 am

    HI Mark,

    What is the complaint of this monitor? When you check on the secondary diode where did you place the meter black probe?


  3. Mark Peacock

    December 23, 2010 at 9:25 pm

    The complaint is no power when you push the power button. On the secondary diode I place the black lead on cold ground. Thanks for your help.

  4. admin

    December 23, 2010 at 11:12 pm

    Hi Mark,

    That was strange because you got a voltage which was extremely too high. Have you try using another digital meter to test it?


  5. Mark Peacock

    December 26, 2010 at 3:52 pm

    No but, I have checked these voltages several times and they all come out about the same reading each time I check. I don't have another DMM I do have an Analog MM. Can I check the voltages with the Analog Meter?

  6. admin

    December 27, 2010 at 3:25 am

    HI Mark,

    Yes you can test it with analog meter.


  7. Benedictus

    September 14, 2011 at 1:25 pm

    Hi Jestine
    My Acer laptop charger is faulty. The bridge diodes were bad. I changed all 4. I even replaced d filter capacitor and power transistor wit their exact replacement, just to be sure. Howeva, when I power on, d fuse trips and d two diodes dat have their +ve end connected to d power supply gets shorted.

  8. admin

    September 14, 2011 at 8:23 pm

    HI Benedictus,

    I suggest ttaht you check all the components in it. When the power fet shorted the power ic will give way too.


  9. Benedictus

    September 14, 2011 at 9:16 pm

    Thanx. I've checked all d other components. They seem to be good.
    Is UC3842 same wit KA3842?
    Secondly, can I replace a 0.022uF, 275V bypass capacitor with a 0.1uF, 275V capacitor?

  10. admin

    September 15, 2011 at 6:57 am

    HI Benedictus,

    Most circuit can work but to some it require the original part number. As for the capacitor, i suggest that you use back the same value. 0,1 uf value gap is too big with the original value.


  11. Benedictus

    September 16, 2011 at 11:18 am

    Hi Jestine...
    I have a Sharp Tv. When I power it on, the power LED blinks three times and then goes off. What do U think is the problem?

    Keep up Ur good work...

  12. admin

    September 19, 2011 at 5:58 am

    Hi Benedictus.

    It can be dry joints in the vertical section or some shorted components in the mainboard. You need to make sure it has good output voltages.


  13. OLA460

    May 1, 2013 at 3:04 pm

    my acer laptop charger have faut when i open it the transistor and resistor that switch the transistor on damage pls what cause it

  14. OLA460

    May 1, 2013 at 5:45 pm

    pls i dont known the value of resistor that couple my power ttransistor and ic uc3842 together pls tel me am waiting have not said this before pls help

    • Jestine Yong

      May 3, 2013 at 10:09 am

      Hi OLA,

      You need to get the schematic to find the value. Or you can get an estimate value base on the schematic diagra on other model that use the UC3842 IC.


  15. Raghunadhan C P

    May 23, 2013 at 6:17 pm

    Hi Mr.Jestine
    I received a sony TV KV-J 21 with a fault of single horizontal line. I replaced the frame IC TDA 8172. It worked for five minutes, then slowly the raster started shrinking from the top as if the whole raster is moving down. After some time it become a single line. I replaced two new ICs. But the fault is the same. Could you fell me what can be the problem

    • Jestine Yong

      May 24, 2013 at 10:54 am

      Hi Raghunadhan,

      Make sure the supply voltage is good and stable and you have applied heat compound. Try resolder all the surrpunding components too. If the ic breakdown again then possible vertical yoke coil could have a minor short circuit.



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