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Electronic Repair Questions/Answers and Testimonials- Part 50

By Jestine Yong on March 10, 2010

Hi Jestine,

First of all I really enjoyed your book ans use it as a reference.

I have over 200 Dell LCD monitors to look after and to find drawings in South Africa is nigh impossible. It is the DELL 51cm E207WFPc. Is there any chance I could buy it off you?

I have two monitors with white screen. If I change the chassis they work OK. what could this be please?

Many Thanks and keep well.

Kind regards,

Dave

Hi Dave,

Sorry i do not have the schematic diagram for this lcd monitor. White screen usually is the problem with the lcd panel (assuming the cable from the mainboard to lcd controller board are connected well). If you have a chasis that have bad board, you can always salvage the lcd panel but the model have to be the same.

Jestine

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Dear Jestine,
Thank you for your effort for supporting me thru your
newsletter monthly. To tell you frankly, you are a great help to my
hobby as an Electronic Technician…. Thank you so much and more
power,

Best Regards,
Ernie

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Hi Jestine,

You are such a wonderful and generous technician that I’ve ever seen. No one has ever let me understand electronics repair skills as you first report I just read did. May your kinds live long to save the world. I’ll confess to you more in my ample time. Regards.

Love In Him.

Josie

Airfield Lighting And Maintenance Engineer

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Hi, Jestine ,

Yes the only different is the color both also 3A

The scope model gw instek gds-820s

If ready MCU problem then i will keep it as a spare unit

Thanks

By the way, I learn a lot from your LCD repair Monitor e-book.

It is a vey HELPFUL & INSTRUCTIVE Book

Thank You very much

Khootp

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Jestine,

You have a really great site.

I have a question regarding LG Flatron L1810 LCD monitor.
The monitor was completely dead.
I replace few components in the SMTP power supply and it back to work, with good 5V & 12V output.
Now the LCD turn on – green LED in the panel, the CCFL are on, but there is no display even no OSD menu.
Do you have any idea?

Thanks a lot,
Aniesns

HI Aniesns,

It could be the Mainboard MCU problem. I came across few units of Samsung that have the same problem.

Jestine

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Hi Jestine thanks a lot for your help and your time

I wonder if you could answer me this another doubth about a proyection lcd tv the model is KDF-E42A10

The problem with this lcd is that there are vertical lines in all the screen it could be the panel

Thanks a lot for your attention.Your friend Mario Muñoz

HI Mario,

Vertical lines is usually the fault of panel and it can’t be repaired.

Jestine

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Hope & Praying that you are good & healthy. I am writing this e-mail to inform you that I & one of my friend is going to start a Computer Institute, thinking you in my mind. You are just like a god to me in this field. Just because of you and your books, I am introducing a electronics course in our institute too. Though I don’t have any electronics background, I never attend any electronics classes, just by reading your newsletters and by your websites; I have got a huge inspiration to go forward in this field. Your English is very easy to understand. I have read each and every word of your site more than 50 times. How you have started your journey in this field. How you have started your own techniques of repairing CRT & LCD and etc. etc. You have just boosted my life, you are my real guru. So I just want you be always near to me.
In one of your blog you have written 7 reasons why you are not successful in Electronics repairing field(Point 2 you didn’t network with other) Sorry to say you sir, no bobby is there to help me, nobody wants to share their knowledge, whenever I got any problem, I have to solve it by my own or by reading your blogs otherwise I have to send it to servicing centre.
Anyway thank you once again for being such an inspiration to people like me, wish me good luck for my institute opening on 3rd week of March. Hope you are reading and waiting for your words.
Yours unknown student
Narayan S

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Hi jestine,thanks again for yuor newsletter,last month subject abaut the feetback circuit,and this month the relay subject was graet .thank yuo very much.

kind regards
Robby.

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HI Ken,

Thank you. You are so nice to help this beginner. I am glad to know that the 3.3 VDC to the main board is correct.

No problem!

You say that “Once the MCU received the 3.3 volt and the vga signal cable is connected then it will send a on signal to the optoisolator circuit to trigger the main power supply. ”

I have found the return path for the signal to the optoisolator (the blue wire) from the main board to the standby power supply. It should turn on the optoisolator for the path then goes to the main power supply to turn it on. I assume the on signal I am looking for is a 3.3 VDC signal here.

Yes it can be that voltage. As long as the signal is more than 0.7 volt it can be used to trigger any circuit that use semiconductor.

What do you mean by vga signal cable? Is it the wire bundle from the Main Board to the Power Supply or is it an external signal cable, as an antenna or computer line that must be connected to the main board for the MCU to work?

Vga signal cable means the Signals coming out from the computer (RGB, H and V signals) and to the lcd monitor motherboard.

Thank you again for you patience and your help for this novice.

No problem.

What part of the world are you in?

I’m from Malaysia- city Kuala Lumpur

Your books have given me great insight into SMPS’s and LCD repair and I am now getting the experience to do better.

Thanks!

Jestine

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HI Julianto,

How do we know watt in a resistor? like 470Ohm 5watt, how do we know
it’s 5 watt if the text on its resistor is missing?

By looking at the size. Generally resistors with the same watt have the same sizes

You said that I have to be carreful a bit when trying to turn on the
psu with the transformer and optoisoaltor removed.Is there anything
danger? or maybe cause a serious damage to the part?

What i meant was that you must know what are you measuring/doing like meter probe ground connect to primary side filter cap negative pin and etc. If you know what you are checking then it is okay.

What is the function of the ceramic capacitor that connected from
primary side and secondary side of the psu?

Main interference can be reduced.

When I want to turn on the
psu without transformer and optoisolator, should I remove the
capacitor too?

No need to remove.

Jestine

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have a LCD monitor but when power on, no lights detected, may I ask what’s the problem?

Hi Bernard,

Have you check the output voltages from the smps? If no output then check all the components in the power side. If there are voltages entering to the mainboard then suspect a bad mainboard especially the MCU.

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hi jestine, thanks for every repair newsletters you’ve sent me; they help me a lot,i’m struggling with hisense tv set that shows light brownish to every picrure and strong colours at the corners (red, blue & green), i checked the little board at the neck of a crt everything seems to be ok, i’ll be very glad to get your assistance.

the other one is on standby mode, it does’nt come on.

HI Mandla,

It could be the problem of picture tube when the tv have rainbow colours.As for the stand by mode problem, make sure there is supply voltage to the Main power IC. If no voltage you have to trace from there.

Jestine

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Hi Julianto,

Can I turn on the PSU and measure the voltage at the secondary side of the transformer,

with the secondary side removed? I mean, I desolder all of the pin of the transformer at the secondary side,

and remove the optoisolator and then turn the PSU on and measure the voltage on the secondary side of the transformer.

If the secondary side doesn’t have any output voltage,could it be caused by fault at primary side?

because the primary side on the tranformer pin have voltage.

No you can’t because it may blow the primary side due to no load condition.

Jestine

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Hi Jestine,

Hopefully you will be fine and your buisiness is going very well.Jestine i’m facing one problem in my smps that is unstablize or variation in 35 V DC and little sound tik tik sound in power supply but 24V DC is stablize no variation in voltage i thought the sound is coming from smps transformer.Please give me solution for fix it.i’m waiting for your helpfull reply.

Regards,

Owais

Hi Owais,

You mean you have two output lines 24v and 35 V and only the 35 v not stable? If yes then check along the 35 v line and look for bad filter cap and also the load that is connected to the 35 volt line.

Jestine

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HI Armando,

I have a question regarding blue ring tester. When testing a good flyback all lights will light contineous or will flash all the ligth only?

It depends on the flyback belong to how many inches of the Monitor. Generally the 14 to 17″ will show from 7 to 8 LEDs. 19″ and above will have about 4 to 5 LEDs

I used the test coil that is included in the set. and my finding only lit all the lights for a seconds and gone out. i mean the light is not continually on while still connected to the coil, is it normal or not?

Try scratch off the coil wire tip as it was laminated and do not have a good contact. If after removed the lamination and the LEDs still go off then the meter may be not fully assembled and need to recheck again. A good meter should show steady 8 LEDs.

Jestine
http://www.JestineYong.com

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Hello Jestine,

Thank you for all the info you’ve shared. These are big help for us. Need help for this one. I have a tv JVC model AV-P29X. fuse keep busted. Already checked the regulator (STR-F6655) and compare with the good one.The regulator is good. Also checked all diodes around the power section and did not found any short. Please help me to fix the problem. By the way, Where can I download service manuals or schematics for this tv. Maybe I need as my reference.

THANK YOU FOR THE SUPPORT.

Best regards,

Bryan

HI Bryan,

Sorry i do not have the schematic. Try remove the power IC and power transformer and turn it on to see if the fuse still blow or not. If still blow try direct replace the posistor and retest. I’m assuming you have already check the bridge rectifier.

Jestine

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Dear sir,,

I thank you for the quick reply

I mean to say that most of the today smps doesn’t come with white cable out of 24 pin and some comes with white cable and those smps which comes with -5v white cable have -5v missing problem my question is where to find the problem I have checked 2 diode and capacitor 470mf/16v all I found ok but still -5V missing

Guide me pl..

With regards

r.h.shaikh

Hi Shaikh,

Missing -5 volt you have to trace from the white cable to the circuit. It can’t be just consist of only diodes and capacitors. It can be resistor turn into high ohm and etc. Sometimes a bad filter cap in primary side may cause this problem.

Jestine

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I am in the process of buying an analog meter but I found a lot of analog meters in the market and I do not know which is the best or at least good one..can you advice me which one to buy and what are the range I should get on these meters. I need it for my shop to test electronic componants. I have a digital meter but it is good to have an analog one too..thanks

HI Waleed,

Get a Sunwa meter that have the X 10 K ohm range. Sanwa is made in Japan (ORIGINAL) and Sunwa is made in Taiwan. There are few models of Sunwa meter. Get the one that is slightly expensive so that it is more reliable.

Jestine

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I purchased a pc power supply to operate a dc motor but supplier now tells me it will not power up unless connected to a pc motherboard and hard drive.

any ideas pls.

HI David,

You may get a used board or drive from computer dealer and turn it on with the help from this link:

ATX SMPS Test

jestine

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yah! i just read bthe downloaded one. it gives an outlook of an smps. can you tell me something about optocouplers and oscillators please…………

HI Himaja,

Try this links:

http://en.wikipedia.org/wiki/Opto-isolator

and

http://en.wikipedia.org/wiki/Electronic_oscillator

Jestine

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HI Anand,

I hope every thing is fine with you and your family.

We are fine thank you.

Jestine, can you pleas explain me step by step with instructions how to use the two meters?
I can’t understand it from the handout

Blue Ring tester- to test the winding of smps transformer, B+ coil, horizontal yoke coil and Flyback transformer coil. When you turn on it will show two led lights blinking. When you test on those coils (coil only have two pins) and expect more LED will light up. If the led goes off or remain 2 or 3 led lights then the coil have problem.

Blue ESR meter-Turn the meter on, short the probes and press the on/off button again to make the reading to zero (initialization). The check the e-cap by referring to the esr meter chart given. The result value should be lower than the value printed in the chart.

Jestine

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Hi your articles are fantastic, I love the interviews with
other electronic repair shop owners, you should have a donate function on
your website as many people love the material you provide

-John

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good morning sir,
thanks for the update by the way sir i have problem with my tv samsung 14 inch it has no color red, pls help me what im going to do i think that is not a hard problem…

thanks..

HI Edwin,

Compare the blue/green circuit in term of signal and voltage with the red circuit. Any big differences is the clue for you to trace out the fault.

Jestine

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HI Abdul,

I’ve d loaded the book. Explanatory and impressive book on SMPS. Now I understand why you took quite some time to compile this book. Nowadays almost all of the electronic equipments are powered by SMPS. That’s the reason I decided to spend money on this book. This book really will help people who are in the repair field.

Thanks for the support and glad that you like the ebook. The arrows and the photos really took me lots of time.

1) What if the Blue ESR meter shows ’00’ when we check capacitors, does it mean short or very good capacitor.

2) I’ve proven to myself that the meter isn’t effective caps in circuit. Better check it out of circuit.

If your meter cable is too long then it will give you the “00” result. Make sure the each cable is 30cm long and i found that the esr meter is very good in testing e-cap on board.

3) What is the function of ‘memory’ capacitor and how does it work. I don’t remember if you had mentioned about it in your ‘Testinf E components’ book.

Could you explain this because i have not come across a cap meter that have memory?

4) HP1925 LCD monitor power LED is there but no display. I found few caps popped up in the P supply area and replaced them but no change. 17 volts and less that 5 volts available at the connector to the main board. One polyester film cap found to have high ESR. Replacing that too didn’t solve the problem. Back light lamps seem good. From the beginning I notice very low light appears on for less than a second and the monitor goes to stand by mode. It’s puzzling to me. Please give a clue.

When it already shutdown does the supply voltage to the inverter IC still present? If not suspect a bad mainboard (assuming the mainboard is getting all the correct voltages).

Jestine

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HI Guy,

It’s been a while since I last sent you an email. By the way ,how are you
keeping?

I’m fine thank you.

I just want to know if you can give me some repair tips on CRT
Television Sets. I really wish we had a training centre like yours here in
South Africa. They presumably have training centres but at a phenomenal
price!! I have been very successful in fixing HI-Fi sets, Radios, DVD
players etc., but when it comes to TVs I become so frustrated for not being
able to point out the problem. I purchased quite a number of books on TV
repairs but still to no avail. For example, I am trying to fix a Telefunken
Colour TV Chassis TX-92F and managed to obtained the Shematic diagram as
well. The problem is; at start up the set comes on but dies out a second
later. I have tried almost everything I know and still can’t find the fault?

Try isolate the problem first using this link:

http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems

If the flyback, HOT or yoke coil shorted it can give such problem.

Jestine

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hi jestine,

how do i determine with the analog and digital meter to exactly known which range or where to use the selector to measure the value of resistors, sometime in my pratice when select 1X, 1K, ect. ect.or other rage i got 2 or 3 different values

HI Exodus,

When test resistor please do not use analog meter. You have to use digital meter which is more accurate. The digital meter have two types autoranging and selector. Autoranging will automatically show you the result. The selector type (manual type) where you have to select higher range to test the resistor. For example, if the resistor is 9.7k ohm then you need to select 10k ohm range to test it. Please do not select 1k ohm range.

Jestine

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good day to you.i have a dell laptop computer model:8600.the problem is when i switch on my laptop computer and boot until desktop appeared,after few seconds monitor gets dim.i can only see the icons and cursor by using flashlight.i suspect that the backlight or the inverter where it connected have problem.what should i do to test both of them using my multimeter.i am new with this problem and i dont want to do anthing to it unless i am not sure of my analysis.i know you are expert on this matter.please reply.thank you.

HI Allan,

Yes you are right, it could be the inverter or the backlight. You may need a good working backlight to compare to find out which section that really give problem. By using multimeter may not be able to locate the fault because inverter board have feedback circuit which is hard to check if we do not have a working backlight or inverter board for comparison.

Jestine

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