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Electronics Repair Questions/Answers and Testimonials-Part 46

By on April 30, 2013

Electronics Repair Questions/Answers and Testimonials-Part 46

Thanks a lot for your help, the main board light turns blue and remains blue. Even when I press power.  I can measure the 3.3 volts going to the main board, but there is no change to the power indicator. Tomorrow I will fix the original power supply to really justify where the problem is coming from. The IC you mention is responsible to control the on and off mode of the power supply. I will consider buy a different main board to justify what you mention. I will let you know the result. Thanks a lot Mr. Young . I like you as a friend you are sincere and honest. I’m proud to have you as a correspondent and a friend. High regards



Have Acer monitor for about 1 year old. The screen makes a humming sound after about 1 second of turning on. Then goes blank. Is this something repairable? and worth it?

Hi Candace,

You may need to open up and check for bulged filter capacitor. It could be dry joints, bad high voltage transformer or even one of the backlights have problem. It is hard to predict which one is the causing the problem unless you open it up and check it. If you have n experience on this I suggest that you send to a repairman.



I have a Haier liquid crystal display hlh406bb. The led light remains green. I ordered a brand new power supply the led stays the same. I need to know what can cause the main board to freeze. The LED supposes to stays red, then change to green.  it’s not suppose to turn green without pressing power.  Where this problem is coming from.  Main board number is 0091802103v4.2. power supply number is Ad301M24-4n1. Please, reply to me some info. Thanks


I’m afraid the problem is in the mainboard. The reason for it is because the signals (red and green) are coming from the MCU IC in the mainboard. If the MCU ic programs is corrupted or have problem it will give out the symptom as what you have seen. If the voltages to the MCU ic is good then then suspect mainboard problem.



Hello Jestine.

Thanks a lot for your help, but what do you mean I have to cut the VGA Cable? did you mean to desolder the conector?

Best regards


Hi Martin,

Some VGA connector already sealed and no way to open it. If yours can be opened then check if there is any broken wires inside. If it can’t be opened then you need to cut it and follow the link below for pin reference:


Dear mr Jestine i would like to thank you for all articles about psu they did help me a lot and about that tester it seems good as i am having too much atx to repair.all i wanted to ask is abt an crt 74cm tv the customer brouht to shop complainent was that the tv just shut down when i test i found diode i think is a damper and the hot transistor and the east and west transistor where leaking and 2 caps so after replacing all of them i swicht on the display was having horizontal lines at the top of screen as it was folding images can you help with this from teboho

Hi Teboho,

Folding images can be caused by dry joints, missing or improper supply voltage to the vertical section. If all checked to be good then direct replace the vertical output ic and retest.



dear sir;

menu lock display in lenovo LCD monitor & menu does not working

what was the problem.


It can be the button fault or the flash rom/mcu corrupted. Try press the menu button for more than 30 seconds to see if it can be unlocked or not.



Hi Jestine, Can a disc cap increase/ decrease in value? I have a brown Disc cap that has a marking of 104? and it measures 77.97nF. From my knowledge this cap suppose to measure 0.10nF. Can I be wrong?

Hi Andre,

Yes it can decrease in value. That cap seems to be out of value and need to be replaced.



Hi Jestine,

could you please give me the specification for a zener diode,

1) A56 or it could be 65A

its marked as ZD on board if possible i need the voltage and watts if you can please help,i did search on the web a lot and replaced with a 56v 1.3watt ,i think i got it wrong,

kind regards


Hi Paul,

Sorry no info on this. It could be a 5.6v or a 56 volt zener diode. If the circuit is using around 5 volt then it should be 5.6 volt. If the circuit is running on more than 50 volt then it should be 56 volt. As for the watt size you can determine it. A 1n4148 size is similar to 1/2 watt. Any zener diode that is bigger than 1N4148 is 1 watt.



Dear sir.How are you,I hope you are fine.Sir i have a query about Dmp
printer.How can i test DMP printer head with multimeter.Please advise
me sir.

Hi Hirak,

You need to remove the printer head and check if the coil winding is open circuit or turn into high ohm. You can test the coil using your ohmmeter.



Hi Jestine:  With this device i can  check  or test  the Hard Drive  Device. Mother Board, Video card and Moden device  or  it is just for the power supply.

Jestine i have another question: My computer it does start,  i press the power switch for  the cpu and start open the data and  then stop and will not continue anymore.The power supply  and fan is working, heat sink fan is working too. I try to blame the video  card or the hard drive, power is ok.What do you thin?

This is Sony  personal computer.

HI Jairo,

The tester is only for atx power supply. In your case, the problem could be in the power supply or motherboard. You need to check for the power supply voltages and make sure they are good and within range. If the power supply is good then you may need to check on the motherboard like make sure the ram is properly seated, no bulged e-caps and etc. The best is to use  PC post card to find the bad section.



Hi Jestine,

the Vizio emblem on the bottom of the TV is what I was talking about. This did not appear on the LCD screen. To elaborate, the backlite does not come on at all. All cabeling seems intact.


HI Ken,

Did you get and dc supply voltage to the inverter ic? If yes then most probably the inverter ic or corresponding components could have problem.



Dear Sir

In your last article (How I Solved LG 21” Television Intermittent Dead Symptom) you indicate a chopper transformer and in your previous some article you indicate SMPS transformer.

Is both chopper transformer and SMPS transformer are same or they are different?



Hi Salim,

Yes they are the same.



Sir jestine,

Sir can you have the idea if how much is the smart tweezer? Can I buy from you? Because in my tv repair. Some board has many smd components and it is difficult to test it without a smart tweezer. Can a ordinary tester like analog or digital multi teater can do the job? Or may the one that I buy from you esr ang the blue. Ring tester can test the smd component?


Hi George,

Sorry I do not sell that tester because it is very expensive about USD 350+. I suggest that you buy directly from the website In fact you can test those small smd components with your digital meter. Just buy the tweezer probes from and connect it to your meter and you will have smart tweezer. The ring tester can’t be used on smd components because it is meant for checking coil only. The esr meter is for checking the big or smd electrolytic caps.



I successfully managed to repair an LG LCD TV by following the steps and hints i read in one of your books.

Hi Abdel,




Hi Jestine. Can you PLEASE HELP ME?. I wonder if you have any tip on Shuttle Computer (motherboard D33032) my problem is this: The computer turn on but nothing shows on screen(monitor) There is no bad capacitors, no  bad transistors. THANK YOU FOR YOUR HELP JESTINE.

Hi Manuel,

I have never repair that motherboard before but just like any other motherboard if you found to be no display it can be bad power supply (missing power good signal), bad rams, programs in bios run or even bad graphic chip, bad crystal oscillator and etc.



Hi Sir,

Thanks for u r suggestions’ have one doubt in panasonicTV.Modelno:21k1400.In the circuit mip2e7dmy(ref for2051)is there plz tell me it is Fet or Transistor.if u possible datasheet available plz send me sir.plz

Hi Bhaskar,

Sorry i do not have the schematic. but this is the nearest I can find:

although it is not the exact same part number but it is from the same family.



Hi Jestine,

the power supply i am repairing is for a DALI  X3E printer controller,

the complaint was no power,

1)fuse was good,bridge rectifer voltage and main filter cap voltage present and correct,

2)no voltage present from power supply output connecter when connected to main board

3)no voltage present at power supply output connecter when not connected to main board,

suspect power supply to have problem,

4)fuse taken out and 100w bulb connected as a load,

5)100w bulb did not light at all nothing,

6)started to check power supply components,

7)found 1ohm 2Watt resistor to be open reading(replaced with 1ohm 3watt)

connected power and 100watt bulb now lights but stays bright,so carry on testing components,

8)found 0.27ohm 2watt resistor to be 0.30ohm(replaced with 0.27ohm 2watt but reading 0.30ohm)

9)found A56 ZENER  to be two readings thought was 56volt so faulty and (replaced with 56volt 1.3watt

10)replaced UC3844AN CURRENT MODE CONTROLLER with UC3844N

11)connected power 100watt bulb lights and stays bright

12)100uf 25v E CAP BULGED AND POPPED(replaced with same)

13)removed 100 watt bulb and refitted fuse and coonected power


15)rechecked 95% of components and replaced all BLOWN COMPONENTS/PUT JUMP WIRE IN PLACE OF VARISTOR   UC3844N REPLACED WITH ORIGINAL UC3844AN

16)put 100watt bulb back as load and connected power

17)100watt bulb lights bright and stays bright no components blown,

18)back to the drawing board,

so maybe components failing under load,or im missing something due to new and inexperience,

Hi Paul,

The primary winding of the transformer could have short circuit. Try let the bulb to on for about 5 minutes. remove the ac input, quickly discharge the big filter cap and now place your finger on the primary side components. The hottest component is the one that had shorted.



Hi Jestine I’ve got 2 tvs with color mix problem . I know sometime is coz of magnetic field nearby then try to degassing using a magnet but still not going off. What else can I do.

God bless

Hi Fitwell,
If demagnetizer can’t remove the color patches then the problem is a fault crt tube. The shadow mask located inside could have collapse.



Hi Drax,

Now I have my question.

1.Can you explain me what is the real meaning of power rail in the circuit?

It is the output voltages line from power supply

2. where I could exactly find the power rail during the time i am checking the short circuit ?

The power rail is located after secondary output diodes. If all other power rail have output and that particular power rail does not have output then most probably that rail have bad or shorted components.

3. Am I right to connect the negative test probe from the multimeter to the cold ground and the positive test probe to the positive supply voltage to find a short circuit?

Thank you  and hope to hear you soon.


That is to check the output voltage. You should connect a x1 ohm meter between cold ground and the power rail and it should have one reading and not two similar reading. Again it depends on what power rail you are testing.



What’s the difference between getting an analogue tester and digital?  I want to get one, and want to make sure to get the correct one.

Thanks Jestine.



Hi Marq,
Both have its own strength. I use digital meter to check on resistor, voltage, ampere, frequency and continuity test. I use analogue meter to check on diodes, zener diodes, transistors and etc.


Dear Jestine

Please suggest how to identify smd capacitor as their is any number or alphabit

Sunil (India)

Hi Sunil,

Try check the link below and read their comments;



during my troubleshooting I found the HOT is defective, so I replace the component, but there is deference in last digit only the letters.

Hi Jobart,

You should look for the main digit. If the number is BU2508DF then look for BU 2508DF. The rest of the number is not important.



Hi jestine

I have a Panasonic kxp1121 printer, after on for long hours, will have power failure, and unable to on. If this type of problems, normally is caused by what?


Hi Eric,

It can be the power supply or mainboard. If it is not working you need to check if the output voltages is still there or not. If no output voltages then suspect power supply. if the voltages is there then suspect bad mainboard.



Dear Jestine Yong,

I would like to express my appreciation for your courtesy in appreciating my efforts. You’re part of an important network of people who always provide the advice, suggestions, referrals, and support that help bring to lives of various people’s dreams and desires.

It is so rewarding when a senior member of a profession takes the time to give back to the field in this manner-and I feel very lucky to be the one receiving the benefit of your experience.

Thank you once again your support.




Hi Mr. Jestine yong,

This is Galwin from india.I am your subscriber of electronic newsletter.Really your newsletter is very fabulous and  useful to me.I want some clarification from your side.Last few days we faced the same issue in all our machine which is the zener diode  get damaged (burnt) intermittently in the smps of robot controller during the machine startup time and  the running time also.Checked everything but could not find anything abnormal.For better understanding i attached the necessary pictures,pls find the attachment.Please help me. Thank you for your reading and considering.Once again i thank you very much for your newsletter and i wishes with full of heart for your prosperous future.

Note;zener diode value – 6.2c



Hi Galwin,
Have you check the surrounding components like the e-caps with ESR meter? From the picture it seems like the zener diode area is connected to another board. Is the other board good? Sometimes components can be checked good but fail when under load. In this case, you may need to direct replace and retest.

Hope this helps.



Dear Jestine,

Thanks for your answer.

I checked that, but the problem isn’t on the board but on the screen side. I compare with the others flat cables and the pins of this input are shorted, around 10Ohms the others are about 8Kohms.

Is it possible the lcd screen have this kind of faulty problem? Or you didn’t get yet this kind of malfunction?



Hi Nuno,
I do came across lots of short circuit in electronics circuit but not specifically in your type of equipment. The troubleshooting method is the same regardless the equipment is. Just follow the line to check for shorted components. If you have a short circuit finder then your job would be much easier.





  1. abbey

    May 4, 2013 at 12:01 am

    Helo sir! Pls sir, I have a SMPS that carries 2 60N60. What can be problem/solution of constant blown of these components at the primary side? Tnx sir!

    • Jestine Yong

      May 5, 2013 at 5:22 pm

      HI Abbey,
      Bad power ic, power transformer and shorted corresponding components. Check also shorted diodes in the secondary side.


  2. Sebastian

    May 7, 2013 at 2:42 am

    I have Hisense 19" lcd Tv that only the volume Down and Channel down works all the other UP buttons and menu Buttons don't respond. I have check the tack switches they are fine. I suspect the main board (RSAG7.820.1264/roh Ver.D) Any clue where to look.


    • Jestine Yong

      May 7, 2013 at 10:00 am

      Hi Sebastian,

      What about using the remote control? Is all other button function?


      • Sebastian

        May 10, 2013 at 5:30 pm

        Hi Jestine
        Thanks for replying, No I do not have a remote.
        This set was give to me without a remote.
        the set has
        1. menu - don't work
        2. Source - Ok
        3. VolUp - don't work
        4. vol Down - OK
        5. ChUp - don't work
        6. ChDn - OK
        7. Power
        Thanks Agaain

        • Jestine Yong

          May 10, 2013 at 9:17 pm

          HI Sebastion,

          Check the button again. If all checked to be good then most probably the EEPROM data could have problem.


  3. Austin onweaba

    December 1, 2013 at 6:32 am

    helo jestine please help me out, my tv set have problem of dopts colored in for the screen i don't know that part i will start to look for the fault.

    • Jestine Yong

      December 3, 2013 at 10:26 am

      Hi Austin,

      If the crt have color patches then the problem could be bad crt tube if it can't be removed by degausser.


    • Mukesh Paliwal

      November 15, 2014 at 10:10 pm

      sir my intex woffer speaker is output sound vry slow how will solution

      • admin

        November 17, 2014 at 7:38 pm

        Try check on the capacitor and volume control.



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