Electronics Repair Questions/Answers and Testimonials- Part 42

I am working on a Hanns-G LCD (i think it is 32″ monitor) and it is not powering on.

I opened the power supply section and started to probe around where the voltage enters and where it exits from the power supply.
I did not see anything unusual. The voltages were 12 , 5 and I think 3.3 but I ended up replacing the whole power supply with a new one and the system still does not power on. Could there be an issue with the on/off button that is wired to the main board ?
Could there be an issue on the main board itself ?

thanks for your help !

George

HI George,

First thing that you need to test is if the mainboard MCU getting supply voltage or not? If the MCU is getting supply voltage and the power LED still does not light up this means the MCU or the flash rom (if there is one) already corrupted. Before that you have to make sure the power button is functioning.

Jestine

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HI Rahimah,

1) did u familiar with brodcasting board which is there has so many smd component and complicated ic’s like programmable ic and controller.

I’m not familiar with such board. I’m more on the consumer electronics board repair. 

2)since this is my first experince to repair this board, kindly i need your expert opinion where should i start to do analysis on this board?

In my experience it is not easy to repair such board especially there is no or limited info about the board. You need:

1) to understand how each section of the board work
2) to be able to test smd components with the right tester
3) To be able to find replacement for the SMD parts
4) to be able to use some specialize test equipment to troubleshoot the board
5) To be able to reprograms on the eeprom, flash or even MCU IC.

Note: sometimes the fault is not on the component, it is due to corrupted programs in those ICs above.

Jestine

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Hi Mr.Yong
Monitor Samsung 510N model as a Picture “No Signal” I have cable after “D-sub” I have no picture of the computer and the monitor turns off after a few seconds.
Can you please guide me to fix this flaw.
Thank you.

Hi Mohammad,

If the supply voltages are good then the MCU have problem. It is common that the MCU have problem.

Jestine

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Hi Justine,

Hope everything is well with you and your family.

 

My friend brought to me a LG LCD monitor model W1934SI with a no display issue. the first time you switch  it ON or plug a VGA cable it will show a display but only for about three seconds and the screen will become black but the power indicator is still ON (blue color).

I tried to use a light to see if there is an image in the screen but there is none. I checked the power supply board for some visual signs but I didn’t see any. The back light turns on the at the same time with the display. I Hope you can spare some of your precious time for my problem.

Thanks and Best Regards,

Romy

Hi Romy,

Sometimes you need to use a powerful torch light in order to see the faint image. If the image still can’t be seen then the problem could be a bad mainboard or the lcd panel which is quite rare to have problem.

Jestine

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this power supply board has the 5v but the 12v and 24v is absent. do you think is a power supply problem?there was a zener diode shorted and resistor burnt but  replaced and there is nothing shorting or burnt now. Thanks

It can be the power supply itself or the MCU of the mainboard. 5 volt is the standby voltage to trigger the MCU to send an “On” signal to turn on the main power supply through a relay or optoisolator. If the relay/optoisolator circuit or even the MCU/eeprom have problem the main power supply will not turn on and you will not get the full voltage of 12 and 24 volt. Again if the main power supply itself is not good (although the other circuitry working fine) then it will not have output as well.

Jestine

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Hi Jestine,
Yes i have already tried resitting all the cables, but it did not help.
Could the power supply still be a possible cause – i have only done a rudimentary test of the output voltage.

Supposing it is the T-Con board…..the characteristics of the problem appears to come on after 5 to 10 seconds after power up.
Turn it off and power up again and the problem appears after 5 to 10 seconds.

For this type of problem, what is the most like cause??  Capacitors ?  or semicon  or both ?
If i want to attempt a repair of the T-con board, where should i start to test ?

Thanks
Yee

Hi Yee,

If the output voltages from power supply are good then don’t suspect power supply. Bad semiconductors could cause such problem. If you have the freezer or hair dryer you can try tackle such fault.

Jestine

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Hi NG,

1.Are you mean measure the voltage of the FB and do the comparison test? When you testing the FB.
2.Do you place the black probe on Hot ground and red probe to FB pin?

Yes but you need to compare with a known good power supply. Usually I do not perform such test. If the vcc voltage is good and no output waveform (assuming i have checked all the surrounding components) I will direct replace the ic and retest.

3.Any alternate method of testing, I am not very confident with this test while power on?

Just becareful. If you have the isolation transformer that would be good. I suggest that you learn voltage testing on secondary side first.

4. Can it be test by supply the voltage to the Vcc such as 30V  and measure the FB pin?

No you can’t, FB signal must come from a working power supply. Pumping in 30 volt won’t cause the power supply to work.

Jestine

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Thanks Jestine for always updating me. I haven’t buy one of your
electronic books yet, but am planning to get one in the future. At the
moment I’m having problem repairing a UPS. I have already replaced it
with a new battery 7.5ah@12v, and still that buzzer alarm keeps on
sounding. I don’t know how to figure out the problem. I guess the
problem is with the board. Can you give me tips on how I can service
it or otherwise, I’ll destroy it. Your assistance in this matter will
be greatly appreciated. Thanks.

Hi Justin,
I’m not sure what model you are having. In some UPS like APC model, once the battery replaced, one need to reprogram the eeprom ic .

Jestine

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I need your advise regarding troubleshooting electronic. I have 1 set tester calibration which fault power trip when close the cover. If i open the cover & lets running 2/3 hours , it is running fine no issue but when i close the cover, it was power trip/no power. Can yor advise me, why it is happen like that & what i suppose to do? Really need your advise.

thanks so much

Hi Hairus,

You may need to check if the cover did touch on any wire or not. Make sure also the components in the primary side are all isolated to each other and not touching the adjacent components.

Jestine

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Hullo Jestine, thanks for your powerful info on electronics repair.

 

First I live in East Africa- UGANDA and intend to purchase your most of your books where possible.

Payment by paypal might convenient for me.

 

Currently am repairing a faulty Minibus auto door controller. I simply realize one of the 4 main transistors differs

because i have compared this faulty controller with a good working one from a similar bus.

 

Faulty transistor number is 2SB833.

Exact transistor is unavailable where I am. Is there another replacement version I could use?

 

The vehicle battery voltage is 24volts. Please advise.

Thank You.

 

Dayan.

 

Hi Dayan,

From my databook the replacement number is BDX68A,MJ11013, MJ 11015 and 2SB694.

Jestine

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Beloved Jestine,

 

While choosing equivalent transistor what are the important things which are to be taken into account.

 

Hi Dhananjay,

It depends on type of transistor. The usual spec is you need to find the same or higher rating for volt, amp and watt. In horizontal output transistor you need to look for almost the same Hfe value.

Jestine

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Hi Jestine,

Tq for your information regarding Damon’s ebook on Lcd repair secrets. Anyway I have one question regarding samsung 21” tv. I ‘ve just replaced flyback and the D5072 horizontal transistor, but it only last one day. The flyback makes an ee sound. Is it the flyback problem again or the access voltage or current from the power supply? Pls

help me. Hope to hear from you soon.

Yours sincerely

RIDO.

Hi Rido,

It can be the flyback, B+ supply voltage, horizontal yoke coil and surrounding components. Please read this blog post:

https://www.jestineyong.com/why-horizontal-output-transistor-in-crt-monitor-get-shorted/

Jestine

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HELLO SIR !

CAN I CHECK 32KHZ OR OTHER CRYSTAL ON MOTHERBOARD BY M.M.? IS ANY OTHER METHOD?

Hi Jitendra,

If you mm got the frequency counter range then you can check otherwise you can’t check.

Jestine
http:/www.JestineYong.com

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hi Jestine,

thanks for the mails you have being sending to me.

however i want to know if there is any equipment that can trace fault and analyses it for repair in electronics such as LCD’s and other television.

for instance the equipment will have screen, when connected to the faulty television it will show the faulty component.

thanks i await your reply.

just MAN.

Hi Man,

Sorry at current no such equipment in the market. 

Jestine

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Hi Jestine, I can’t seem to find this problem or solution on the net. The top quarter of the tv is a dark band, any image or text appears to be stretched towards the top. If the channel is switched to a blank channel the screen will immediately turn black but the top will slowly fade to black. Any ideas? I can send you a picture in a day or two. BTW how do I send it to you.
Regards
Eric

Hi Eric,

It may be the T-con board have problem. Try reseat the LVDS cable. Or you can try use hair dryer to blow on the T-con board to see if there is any changes in the display. If yes then most likely the T-con have problem.

Jestine

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HI George,

Are power supplies a more common failure repair vs a T con board/ inverter board / Main logic board or any other board on TV or monitor ?

Yes.

Is there a trouble shooting guide for those boards as well ?

The nearest guide for LCD TV that I can suggest is:

LCD TV REPAIR SECRET BY Damon

LCD TV SMPS by Damon

For power supply repair only I can recommend my ebook  Power Supply Repair Guide

Do problems on other boards effect the power supply function ?

Yes if there is shorted component or the MCU in the mainboard have problem. If MCU in the mainboard have problem it will not send out an on signal and the main power supply will not work.

If you have a short, for example on the main board, could it effect the function of the power supply  or a section of the power supply ?

Yes definitely because any short circuit or shorted component can pull lots of current and this will cause the power supply to shutdown.

Do you cover this in your report ?

Yes I have case studies in power supply repair guide ebook but i use CRT Monitor as a guide and not LCD TV. Once you know the principles you will know the rest.

Jestine

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hi jestine, how are u? hope well.

I had a problem with a SONY display unit model PDM-5000. there are 4 black band on the screen during the operation. I’m suspecting the T-CON board. need ur opinion. and also were can we find the parts.

The second problem is with a SONY MEDIA RECEIVER model MBT-MR1. It is not caming on, no light on the front panel.after diagnostoic i realize the power suplly is providing the power good signal but a signal which is suppose to activate the relay is not present. i follow the line till the mother mother and was confuse ( cannot track the signal, may be due the multi layer board) what can u advice me.

 

Thank u for ur support.

Hi Marcel,

I’m fine thanks. In the first case, if the OSD menu also affected then the problem is in the lcd panel. If not affected then the problem can be in the t-con board, lvds cable or even motherboard but chances is high on t-con board.

In your second case, the problem could be in the MCU/flash rom in the motherboard because this MCU should send an On signal to trigger the relay. If there is good supply voltage to the MCU and the relay still not energize then most probably you may need to replace the motherboard.

Jestine
http://www.JestineYong.com

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when i power on the tv i feel the high voltage present infront of
screen but there is no display heared a loud sound in flybak and the
audio sound like supermario then they stop after a second no display
at all i substitute the flybak but still the eror same when i remove
the yoke i slowly turned on the screen knob i see a circle light at
the center screen but still no display nor sound i dont know where to
trouble pls i need a guide pls help me sir thank you

 

Hi Fred,

The high voltage can be shutdown after sometimes. In your case I suggest that you check the horizontal yoke coil since you mentioned you have replaced the flyback and could see a center screen. No matter what, the output voltages from the power supply has to be good and stable.

Jestine

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Hi,

I bought a 50 Inch Panasonic Neo Plasma full Hd 3D last 2 month. As i came home yesterday my daughter said that while they are playing with her brother, she accidentally throw a handphone on the TV. Now the panel tv crack and when i try to switch on the were noisy sound come out without the picture. Can i claimed a warranty from panasonic?

Hi Mohd,

This is the customer fault and I guess it will be hard to claim warranty.

Jestine

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Hi Jestine,

How are you doing? Hope your are fine.

I just started experimenting myself to repair a Sony Trinitron crtv model KV-XG29M50. When I opened the back cover lid and started checking each and every components on the circuit board, came across 3 units of resistors around the FBT that looked worn out.After replacing them I found the problem is still there.The standby timer / indicator red light blinks twice every couple of seconds.Then I tried checking all the soldering points underneath the FBT. Found one point (no.12-no pin) without solder,I just soldered it.Still no change.Then I tried to check the HOT on the heatsink near the FBT. When removing it one of the pin broken(out of the three pin).Do I need to test this HOT further or just replace it? If yes means,please suggest how to get the original part online.Your troubleshooting advice/tips is most appreciated.

Thanks and Best Regards,

Chandran

Hi Chandran,

I’m fine thanks. If the HOT pin already broken then you need to replace one. You can try order from UTSOURCE.NET. 

Jestine

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Thank you for all the help you have giving so far. I want you to know I only do this as a part time job.

I went the last week end and check the TV it has a good picture but the color cannot be adjusted, only blue and pink on the images. I add a photo of the screen

Thank you

Since you mentioned the OSD menu is good then the problem could be t-con board, main board or even bad lvds cable. Try reseat the cable first before check/replace the t-con board. If it still not work then the mainboard is the cause of the problem. Check out the basic lcd tv link:

http://www.electronicrepairguide.com/lcd-tv-repair-basic.html

Jestine

3 Comments

1. 

   lyn

   August 31, 2016 at 10:06 pm

   hi
   i just started in consumer electronics field

   so im trying to fix this dead tcl after replacing
   the shorted regulator i got the standby but theres only a flash in the middle of screen then everything goes black.
   checking the collector voltage it is too high, what could be the problems..
   im also worrying about the way i installed the new optocoupler i might have put it the wrong way
   also the value different the original is pc123 and i replaced it with pc817

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   Reply
   • 

     Jestine Yong

     September 1, 2016 at 9:29 am

     Hi Lyn,

     What is TCL? What was the original complaint? What was the regulator part number?

     Jestine

     Likes(1)Dislikes(0)

     Reply
     • 

       lyn

       September 5, 2016 at 9:08 am

       tnx for thw quick response,i can really count on you
       everything is fine now after replacing the pc817 with pc123
       anyway tcl is a crt tv

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       Reply

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