Electronic Repair Questions/Answers and Testimonials – Part 26

By on December 28, 2008
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  1. LEE

    January 4, 2009 at 7:10 am

    Hi Justine
    I have found your electronic test ebook quite handy as a reference .

    Theo was asking about programming to hardware level.
    I suggest he check out http://www.parallax.com/tabid/295/Default.aspx
    and http://www.rev-ed.co.uk/picaxe/ .
    A friend of mine use's Picaxa micros in his own circuits for industrial machines he makes.

    I also have a repair problem.
    I have an Hitachi 19 in CM715 that has started to flicker between normal
    and purple. can you point me in the right direction for diagnosis & repair.

  2. admin

    January 6, 2009 at 9:11 pm

    Hi Lee,
    Thanks for the links!In your case it could be a vga cable connection problem (loosen wires internally in the vga cable or connector) or loose connection flex cable between the mainboard and the lcd controller board.


  3. khalil

    January 10, 2009 at 11:20 am

    Hi Sir,

    I have a Dell 17″ Model P790 monitor. When i ON it, it blown it's fuse with in second.

    Please guide me, where is fault in this monitor.

    Have a nice day.

  4. admin

    January 10, 2009 at 1:33 pm

    Hi Khalil,

    Please check the bridge rectifier and if you have the time check all components in the power side. Sometimes a shorted secondary diode may also cause the power fuse to blow!


  5. irwan

    February 8, 2009 at 2:04 am

    Hi Mr Jestine. Currently i am repairing a SMPS model NFS40 for rotor monitoring system. There are not output voltage for 12v and 5v. Tried to replaced the MOSFET but still dont work. Main fuse not blown and UC3842 Vcc is available but it wont come alive. Can you give me some idea what else to check? I'm stuck in the middle. Thanks in advance!

  6. admin

    February 10, 2009 at 8:29 pm

    Hi Irwan,

    If you have check all of the components in primary side then i suggest that you check on the primary winding of smps transformer too. Sometimes a shorted components in the secondary output rail could cause no power symptom too. Hope this helps!


  7. Rudolf Seget

    February 13, 2009 at 8:23 pm

    Hello all,

    Could you please send to me a recomentation how to replace LD7575 device used in SMPS of LCD monitor. This device in no available in Czech Republic.


  8. admin

    February 13, 2009 at 11:01 pm

    Hi Rudolf,

    Try email lavinci at info@lavinci.it for the part.


  9. assad

    February 16, 2009 at 5:55 pm

    Hi! i have a problem with a computer motherboard. the capacitor on it were blown up and on top of it some brown liquid-like oozing from it. If it possible to remove and to resoldered a new one? cause the motherboard always failed when booting up the pc. thnx!

  10. admin

    February 17, 2009 at 10:07 am

    Hi Asad,

    Yes you can solder a new one but before that make sure the power supply produce output voltages within its spec if not a new cap will blow again.


  11. hans

    April 4, 2009 at 3:16 am

    Great site!
    I found (via Google, search for 2008118105925756.pdf) the part list with schematics for 19" LCD's such as Neovo F419 and some ACER models at the following URL:


  12. admin

    April 4, 2009 at 2:41 pm

    Hi Hans,

    Thanks for the link!


  13. RM

    April 20, 2010 at 1:32 am

    I have a 100 mhz oscilloscope and no experience using it. I would like to use it to test crystals on motherboards (14.318 usually). It is a phillips scope with an auto adjust feature. How could I use this scope to test a crystal? What other components might I be able to test with this scope? I have no experience with scopes at all, and most of the information I found online just confuses me more. Thanks!

  14. admin

    April 20, 2010 at 8:21 am

    HI Rm,

    I guess you may have to play around with the setting. make sure it is selected to Ac and try the time and volt per division knob till you see a sinewave.


  15. RM

    April 20, 2010 at 8:52 pm

    Thanks for the quick reply. I have observed this "sine wave" before. It was simple. I hooked both of leads of the scope to the crystal, then hit "auto adjust". Then I saw a sine wave. I didn't have to know anything else about the operation of the scope. Does simply seeing this sine wave mean that the crystal is good? Could a faulty crystal still show a sine wave? I plan to do a lot of additional reading on oscilloscopes and waveforms. I'm currently devoting most of my time to identifying and replacing bad SMD components. I ordered a new wave of meters to add to my arsenal. I just ordered the Blue ESR meter. I already have the Leakseeker 82b, but it's going to continue to collect dust until I have time to sit down and tinker with it. I also ordered a new meter - the Fluke 117. I also ordered a kill-a-watt. I'm hoping to use that to, at least grossly, observe the current draw of a circuit (I work on laptop motherboards).

  16. admin

    April 21, 2010 at 9:01 am

    HI Rm,

    If you could see the sinewave then generally the crystal and surrounding components are good. If you have the frequency meter which is much better because you can test the exact value in Megahertz. Yes, it is good to get more meters and this can cut short your troubleshooting time.

    Have a good day!


  17. Pravin Jariwala

    October 12, 2011 at 5:39 am

    Dear Sir,

    What is the solution for two transistors 2SC4834 for Sony KV S29MN1 in SMPS? Any equivalent that is available in INDIA ?

    --With Regards
    Pravin Jariwala

  18. admin

    October 12, 2011 at 6:02 am

    Hi Pravin,

    From my databook, the equivalent number for c4834 is BU306F, BUT12 AF, 2sc4130 and 2SC4161.


  19. chandrashekar

    October 24, 2011 at 8:25 am


    In sony klv 32t 400a lcd tv, 8 times Tick sound coming and Red lED lighting up but NO disply,No sound pls. help me

  20. admin

    October 24, 2011 at 12:30 pm

    HI Chandrashekar,

    Try this link to isolate the problem:


    Sony set usually use blinking LED to indicate where the problem section is. I suggest that you look for the service manual to locate the exact faulty section.


  21. jeff

    May 12, 2012 at 4:03 am

    hi jestine
    i need substitute for sg5841 any suggestion? can u email me dinodinero18@yahoo.com thanx

    • Jestine Yong

      May 12, 2012 at 10:20 pm

      Hi Jeff,

      Try SG6841. The best is to use original. You can try order online at logictoyz.com or utsource.net


  22. Biswarup

    December 26, 2012 at 12:37 pm

    Hi Jestine,
    Merry Christmas to you and your family. I hope you are enjoying christmas evening.
    I have got a funny problem with a Lenovo G530 Laptop. Details are as below : 
    1. Power on from battery power only, no problems occured. 
    2. Plug in power adaptor to the laptop while laptop is on / off without any AC supply, no problems occured.
    3. If the laptop once receive the power supply through the adaptor, it shows charging, which is also quiet normal.
    4. Now, Switch off the AC line, the charging indicator on laptop, power indicator on adaptor is glowing continiously. At this time the charging indicator on the taskbar shows that the laptop is plugged in, but it is discharging.
    5. Now, I have disconnect the DC power jack from the laptop, same behaviour occurs as above (4), except  the indicator on the charger, which goes off as usual.
    At this time i have connected a multimeter to the laptop DC power jack, and receive 14.6 return voltage !!!
    After shutting down the laptop, the charging indicator lits continuously, and needs to disengage the battery to stop all abnormal activity.
    Do you have any idea about which area / component of charging section on motherboard or any other section creates this kind of funny problem.
    Waiting for your reply.
    Thanking you in advance.

    • Jestine Yong

      December 28, 2012 at 3:58 am

      Hi Biswarup,

      Have not seen such problem before. It could be the charging section or any surrounding components problem. You just need to open the Laptop and begin to check on each of the input/output pins of charger ic and see if there is any abnormal signal within this area.



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