Hi Mr yong i must say the september article was very helpful and motivational u make my week man , i want to join a forum so much and dont know which one to join . any suggestions? forums that discuss lcd tv and plasma tv .GOD BLESSS YOU.

HI Devon,

Try this forum:

http://forum.eserviceinfo.com/

Jestine

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HI john,

SMPS means switch mode power supplies.

and where do i find the B+ supply?

The B+ is at one of the output voltage of smps.

and how can i trigger if my plyback really works?

The flyback only will work if there is B+ supply voltage and pulse waveform to the base of Horizontal output transistor.

sorry sir, for so many questions… im just new in this profession,, i love electronics so much

but i think its really hard to do..

I suggest that you get  the tv repair book by Humphrey to speed up your repair knowledge.

Jestine

==============================

Good afternoon

It is my pleasure to study electronics, but not have enough money tu buy your book in this moment. Sorry for me.
If you can help me, I have a defective Dell 1504FP.
At the begening the monitor starts and gets into stand-by after 1 second.
Now, after I resolded a few components on to Inverted board and Main Power board it does not start anymore.
Monitor Starts but only in Stand-By. Orange ED is ON.
I’d like a schematic and any instructions if you can.

Respect,

Rebegea

HI Regegea,

Sorry i do not have the schematic. Orange light means there is something bad in the MCU or the VGA  cable H/V signal may have broken but chances is high the MCU program may have corrupted. Before that make sure all the voltages to the mainboard are constant and stable.

Jestine

=================================

I’m one of your web surfer and had bought several meter&book from your web site. Currently I’m facing problem on Samsung 29 inch TV model CS29V10MG. Initially the problem is no power symptom and I had check and change 3 secondary filter caps, 1 power IC 5Q1265RF and rewinding the power transformer. After firstly turn on the picture was back as normal, unfortunately around 10 minutes I could detected that something like current leakage to the ground, heat sink and video in/out at the back while touching it. This leakage seems like become greater with normal picture when the TV been turn on many time or long hour. Reconfirm the transformer primary winding and it was full LED light up, all replacement caps esr also OK. Is there any possibilities due to power IC different manufacturing d/code or any other section?. Really appreciate if you could advice on this.

Thanks & Regards,

Fahmy

HI Fahmy,

First you need to make sure the power supply is generating good output voltages. By the way, you mean that you found the power transformer primary shorted and you sent it for rewind? It could be the transformer problem if the output voltages are not good and all the components in the power side already tested good.

Jestine

=================================

HI JESTINE
the shape of these ic s  DPAK , PDIP, SOP,SW, T0220 T02206. SO, SO4………………………………….and so and so
regards
beh

HI beh,

Try these links:

http://www.mikroe.com/old/books/keu/07/7-02.gif

and

http://www.sparkfun.com/tutorial/Selecting-Package/ic-chart.jpg

Jestine

================================

Dear Jestine,

Have you come across the problem where there is power but instead of
the blue screen we get a red screen (this is another difficult problem
with a NEC crt tv screen that is very new to us and we have checked
the power supply.
Can you help me please.
Thanks
Samuelu

HI Samuelu,

No matter which crt tv the procedure is still the same. Compare the RGB cathode at the crt board in term of voltage and waveform signal. Any different in the voltage and signal is the clue for you to begin troubleshooting. Sometimes a shorted tube also could cause such problem.

Jestine

==============================

Hi Dear Sir,

I am reading your book.Its very intresting and easy to understand.

sir,i have a LCD monitor (SAMSUNG sync master 150N).It has no power.what  should i do?

Beast Regards,

Saad

HI Saad,

If there is no output voltages from the power supply the best is to check all components in the power supply side. make sure the fuse, bridge rectifier, power fet (if have) are good. Some model only use a single ic where the power fet already built in. If all components check to be good then direct replace the power ic and retest.

Jestine

===========================

Dear Sir,
Recently i got benq 17″ LCD monitor to service with no power
symptoms. I check the power board, no secondary voltage come out.
Primary filter hold the voltage for long time, so I think switching
components are not working. I check power FET, SM Transformer and
other pram & secon components, all seen well but little confusion with
a SMD IC in primary that is LD7522ps. I think is an oscillator IC but
i haven’t CRO to check it. Any advice to check it and diagnose the
problem. I am waiting for your soonest replay.
Thank you,

Hi RAHUL,
If all the components check to be good then the greatest suspect is the power ic. Usually a replacement will restore back the power. To check it the ic must have supply voltage input and pulse waveform at the output pin (assuming all the corresponding components are good).

Jestine

=============================

Hi Jestine Yong,

Please tell me what the fault is and how I can cure it. There is a
monitor (17“), It bear the problem that it takes long period of time
in turning ON (about 15 -20 minutes) after providing it Power. When it
turns ON after 15-20 minutes, a sound of “Tic” heard( Relay Sound).
Also, when I provide it power its main LED Indicator just blinks in
irregular pattern. I thought there is problem in Power supply. Please
guide me how can I diagnose this fault? I shall be very thankful to
you. Please reply me as soon as early possible b/c it is an urgent
complaint.

Regards,
Muhammad

HI Muhammad,

Please refer to this link:

http://www.electronicrepairguide.com/testing-flyback-transformer.html

Jestine

=================================

Hello Mr. Yong,

Here is the image of the power supply. I havent checked all components yet. I do however wish to learn or obtain some idea on how this circuit works. Your help is greatly appreciated.

Sincerely,

Coedy

Hi Coedy,
Thanks for the photo. First the power ic must get dc supply voltage (about 12 to 20 vdc) then it will output a pulse waveform to turn on/off the power fet so that the transformer primary winding can be energized and be transferred to the secondary side as ac volt. The diodes at the secondary side will convert the ac to dc. So in your case have you check if the power ic is getting any dc supply voltage? Have you check all the secondary diodes and make sure not even one shorted?

Jestine

===============================

Please i need your help, i have a tv set with no display problem, after replacing a suspected ic LA7840 with the same type, the CRT recieve power when switched ON, but producing shooting sound when trying to display and goes OFF. Please what do i do?

HI Danito,

Try put back the original ic and check if there is any high voltage or not. No display can be caused by no high voltage symptom. In order to have high voltage the flyback need B+ voltage and pulse signal from h.oscillator ic to the base of HOT.

Jestine

===============================

Hi Jestine,

Thank you for your newsletter.    I am now troubleshooting the Samsung problem of power pilot light are flashing rapidly and no screen.  I found the pin6  Vstar of  the power switch DM0565R are flashing all the time as well.  I suspect the power switch is faulty and causing the problem.  Do you think so?   Please see attached circuit.  By the way, for SMD BD102, what is the BD stand for?

If you could give me the suggestion, it will be great.  Thank you for your time.

Ricky

Hi Ricky,

If all components check to be good then direct replace the power ic and retest. Make sure also the secondary diodes and the transformer primary winding are good. BD can stand for bridge rectifier or BEAD (small inductor). So it depends on the legs of the component. if it has 2 legs then it is a small coil (inductor).

Jestine

=================================

Hi Dear Sir,

I hope that you will be fine.Sir i don’t know how to check which winding of the transformer is primary and which one is secondary.Kindly guid me.

Best Regards,

Saad

Hi Saad,

Secondary winding is located at the secondary side. Primary winding is located in the primary side. So which one is primary winding? Simple-trace from the big filter capacitor positive pin and you will reach one pin of transformer. Next look for the power fet center pin (drain pin) and trace from there and it will reach another pin of the transformer. Thus both the pins are the primary winding.

Jestine

===============================

HI Roke,
Apologize for not getting back to you sooner.  I was out of state for awhile.

No problem.

Anyway, I am now checking the backlight inverter boards (4 ea.).

Semiconductors checked out okay.  Checked the HV transformers with an Anatek Ring checker.  Some are showing ringing with yellow LED which

signifies as a ? mark according to the checker.  With your experience with Anatek Ring checker, what is a good indication on the checker with these

transformers?  Some also show all the LEDs lit. Still working to find the culprit.  Need your expertise.

It depends on the model and design. A good transformer can have yellow and even red led. Since you have both transformer you can compare the result.

Jestine

===============================

Hi,

I had read your article about testing board to find shorted component using DC Regulated Power supply

and I would like to try in computer motherboard. But there are few question before I try,because Its not detailed explain in your article (I’m new in electronic field)

the question are:

1. The vcc in motherboard ,which one I shoudl connect?(there are 20 pin)

Try the red color one first (5 volt)  before moving to the blue, yellow and etc.

2. Which ground I should put the negative probe?

To the black wire.

3. When start testing, how to set the power supply current first? before start to turn the voltage  knob? I mean, do I should start with setting the current in let’s say 0 Amp? 1 Amp? or…?

Usually i do not set the current, once the voltage is slowly brought up and if there is a short circuit the current will automatically rise very fast.

Jestine