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Electronic Repair Questions/Answers And Testimonials Part 10

By on August 20, 2008

Hi Jestine,

I have 2 LCD TV’s and all the PSU O/P voltages are present 24v, 12v, 5v, 5v standby, none of them are fluctuating up and down. All seems ok with the PSU except that both units are stuck in standby. Any ideas, I would be grateful for any tips you could give me.

Thx

A.

Hi A,
I have never repair LCD TV before but what you have described i have seen it many times in LCD Monitor. The problem was in the Main board and the MCU was the caused of the standby mode (power LED doesn’t turn green). Hope this helps!

 

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Proud to have an advisor like you for continuously support on troubleshooting TV Set.

You are welcome!

Sound like I not so familiar with this symptom ( Do you hear any high voltage sound rushing out? ) but i will pay attention to this issue. If this is the case, what is going on?

If there is high voltage (24kvdc) then checking the HOT area would be a waste of time but in your case since you said you found a transistor shorted i guess the TV should not have high voltage anymore.

For the Inductor Coil, I found the Inductor Colour Code for our reference. Please see attachment for further understanding.

Thanks, if it is the colour code then it is more likely similar to resistor coding, if it is in numeric then only the manufacturer would know the coding.

For the Mosfet Transistor, It should be no problem for me to get the equivalent part number for replacement at Pasar Road. Thanks again for your guideline. For the HOT, Thanks for your confirmation to make sure that the parts is belongs to HOT and not Mosfet Transistor.

No problem!

As for my final question, I found out there have got open circuit on resistor for my TV Set which is belongs to “carbon Composition Type”. If i would like to replace with a film type resistor (Reason: old parts and not convenience for electronics device usage), what power rating should i use? Please see attachment for the picture diagram.

You should use one level higher from the original one. For example a 1/2 watt you use 1 watt and a 1 watt you use 2 watt.

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Message: The article “How To Repair ACER AL712 LCD Monitor With Display Shutdown Problem” works also fine for the Acer AL1715. The capacitors are named C924 (470 µF, 16V) and C922 (1000µF, 16V). Attention: the C922 mustn’t have more than 20mm height.

Greetings thanks’ a lot for your site 🙂

S.F

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Hi Jestine,

I went to Sim Lim Tower but unfortunately none of them sell the smd type power ic (203D6 PVER). I further diagnose the board and notice that there are voltages on the hot side, e.g.: FET transistor’s legs, and the switch mode power transformer legs. But there is totally no voltage at the secondary side, e.g.: legs of the switch mode power transformer. Can we conclude it must be the due to the power ic? Is there any other way to conclude if it is due to other faulty components? Please advice.

It would be a waste to throw away a 19″ LCD if I can’t get the faulty component parts?

 

Hi W,
Since there is not many components in the power side and assuming the secondary side output diodes were tested okay then chances is very high the power ic have problem. From my repair experience, a blown POWER FET would usually destroy the power IC too. If you have the scope you can check if the power ic is producing any wave form or not. If you have other questions please do email me again.

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Hi,

I have a E70 viewsonic monitor that hopefully you might be able to help me with. The contrast has gone to min setting, it keeps popping up on the screen. The monitor has 4 buttons #1, up, down, #2. #1 opens the page to do fine tuning picture settings up-down to get to which one you need and 2 to select it, and then up-down to adjust. But I push #1 to close contrast main opens, 1 again to close and contrast comes back. Will I need to reinstall the monitors start up CD? Thanks for your help, keep up the great work.

 

Hi Bob,
Try checking all the micro switch contacts in the Monitor. I came across one but different brand that out of sudden the menu pops up. I replaced the four pieces button and solved the problem. Sometimes it could also be a corrupted eeprom data that had caused the menu and the contrast setting to behave intermittently and you need to reprogram the eeprom ic. Don’t overlooked too any dry joints in the cpu and the eeprom area. Make sure also the cpu crystal frequency is correct by testing it with a frequency meter. Normally reinstall would not help in this case. Have a good day!
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Hi M,
Thanks for the support on my ebook. Here are your questions and answers:

My Question is , are those LCD Monitor Panels have all the same way of disassembling or opening it.

Most of them are but in some models you have to be a bit flexible and carefully removing the cover.

I have an HP LCD Monitor with a Model # HP w 1907 v , It has a problem within a few seconds when you turned it on it immediately becomes dim. .I really want to inspect it visually since I have an experience in repairing electronics equipment before . I bought the said monitor in Saudi Arabia last September 2007 and it was working very well. I send the monitor through a Freight forwarder las March 2008 and rcvd. the said monitor on May 2008 I open it up on June 2008. Because I was not able to open it immediately because I went to my wife’s province for emergency reason. It means I open the monitor in the box 1 month after it was delivered to my house. I already bring this monitor to the HP service center here in the Philippines & they told me that it cannot be repaired and they say that the cost for the repair is large enough to buy a new LCD.

Actually it is still under warranty because it did not yet reach for 1 year usage. It was used very seldom and it is still very new.

I really want this monitor to be fixed. Since it was my souvenir from Saudi Arabia. I even have a doubt that from that service center that they even told me that it cannot be fixed. Thats why It was a big challenged for me to try to fixed this monitor.

Where can I get also some schematic diagram or even block diagram just as my guides in repairing LCD Monitors, it looks like that it become a challenge for me to repair LCD monitors. And I really want to take this seriously.

In your case if the display becomes dim after few seconds then please follow my instruction below:

Once it has turned dim you must check the supply input of the inverter ic to see if the voltage is still there or not. If no voltage then chances is high the Main board may have problem because it stopped sending the “on” signal. If the supply voltage is still present even though the display already dimmed then suspect a bad inverter ic or surrounding components. From my experience, inverter ic seldom have problem and mainly was due to a bad backlight. Try swapping a backlight and retesting again. In certain brand of LCD Monitor like dell, acer and Ben Q the board have a common fault of shorted push pull transistors with the part number of C5707 and the p-channel FET and also the tuning capacitor. Your LCD Monitor may not have these parts but it could have the FET that built into an 8 pin SMD IC. You may compare the resistance between the top and the bottom circuit. A shorted IC has many resistance reading. By the way, check also for dry joints, loose connection and filter cap for high esr at the secondary side of the power supply.

First I want to know how I can open the or disassemble the said Monitor Panel ? Can you give me an instruction step by step on how to open the said lcd panel?

The step by step to open LCD Monitor cover is mention in my ebook at page 76. =================================================================

 

hi jestine if i want to test smd parts on a laptop motherboard using an oscilloscope how is the power provided?. do i have to have the laptop switched on or does the oscilloscope provide its own power source to test the part under test? im asking this as i have not used an oscilloscope before.

Hi Paul,
You have to power On the laptop in order to test the smd components. If you want to test motherboard without power “on” then you can use Huntron tracker at http://www.huntron.com

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When working with some electronic boards I come across some LEDS labelled Tx and Rx, what do Tx and Rx stand for?

Hi C,
They are transmit (Tx) and receive (Rx).

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…and kindly assist me what other ebooks i need to buy with you i’m cellphone tech but trying to shift in electronic other than computer and cellphone due to very low income in this field to due very low charge of other and a lot of tech in our country only cellphone tech you can see in every corner here.

If your testing of electronic components is not strong then i suggest that you get my testing electronic components ebook as once you have become good in testing electronic components, you can in fact repair many type of electronic equipment. What is the electronic equipment you want to venture in? Once you have sure of which field you want to be in then go full force on that equipment and get the most books on that subject. If you like TV repair, then get many books about TV repair. If you have other questions please do email me again.

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Hello Jestine,

In your eBook you wrote:

“Always treat electrical circuits with respect! If you don’t know what you are doing in areas that could prove dangerous then don’t do it. GET MORE INFORMATION or ask a friend to show or guide you…” While reading your eBook I realised that I was confused about HOT vs. COLD ground.

My research using the internet increased my understanding, but didn’t increase my confidence.

I think I understand that “ground” can mean:

1. A ‘common’ connection, but not connected to Earth.

2. A connection to the power supply. (i.e. usually to the negative terminal)

3. A connection to the inside of a shielded metal box. (i.e. chassis?)

4. A connection to a metal stake driven into the earth. (or a connection to a metal water pipe which extends out of the house into dirt.)

Although I think I can identify COLD ground based on the information above, I don’t want to guess which one is HOT ground. There are also some devices that don’t use that 3 prong power plug, and I am guessing that in those devices, GND is a common connection that can be found using meter continuity. However, knowing that multiple GND exist in the same circuit AND without a schematic I am unsure. Please help me match one of the 4 definition above to :

COLD ground.

HOT ground.

Ground in device that does not use 3 pin power plugs.

 

Hi Y,
Here is one website that can explain some meaning about ground at

http://en.wikipedia.org/wiki/Ground_(electricity)

Okay lets take this simple explanation:

For any electronic equipment that uses the 3 pin power plug and have the switch mode power supply in it then the primary side ground is HOT GROUND and all the secondary side is COLD GROUND which include the casing, chassis, metal shielding and etc. If the equipment that uses only the live and the neutral like a VCD player that use a linear transformer then the cold ground would be at the secondary side where one AC OUTPUT connected to diode/ bridge rectifier to produce voltage and the other line would be to the ground or COLD ground or to the chassis. Hope this helps!

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The inverter IC is OZ960S. I couldn’t find the datasheet but I have a similar datasheet OZ964.

Pin #5 VDDA should be 5V ….. I have 0.0 V

Vin (at F1) is 12V standby. When I turn on this monitor voltage is moving from 23 to 30 V.

Thanks for your help.

Hi R,
If the supply voltage that you got was zero volt then i guess you have to trace back at where the 5 volt have lost. Sometimes a shorted IC or surrounding components could pull down the voltage. The best is lift the supply pin leg of the Inverter IC and power On again to see if the voltage is still zero volt. If the voltage come back then suspect a shorted inverter IC. If the voltage still remains zero then you need to trace backward to see if the MCU is sending the “on” signal or not. If no On signal then most probably the MCU may have problem assuming the MCU already get the right supply voltages like 2.5 v or even 3.3 Volt. Hope to hear again from you. Have a good day!

 

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Sir Jestine,
Good day sir. Hope everything is fine! I have a question regarding crt monitor without high voltage. I have here a HP 17” monitor i check the power seems ok all secondary dc out normal, i check the HOT ok, the drive voltage at the base of hot ok, heater voltage ok, i also check the primary of fbt. But no high voltage. Sir can you help me what to do. Thanks a lot god bless

 

Hi V,

Please check also the B+ supply voltage, if there is no b+ supply voltage the flyback would not be able to work. Here’s another reason why there is no voltage. Please visit this website as a shorted internal capacitor could cause no high voltage symptoms.

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

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Sir thank you for the report you have send just want to ask something about this lcd of mine. It has power and it shows flashing of picture for may a 2 seconds time then it goes black out. can you help to fix this problem. the model is EPRO from china.

 

Hi Danny,
The LCD monitor problem could be cause by a defective backlight as a bad backlight would cause the display to shutdown. Check also the surrounding high voltage transformer area for dry joints and make sure the corresponding components like the transistors and tuning capacitors are good. Bad filter capacitors in the secondary side (filter section) may also cause the display shutdown too. Hope this helps!

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Hi Jestine,

Thanks for your last E-mail. Just the E-mail send to me has really been a great encouragement to me. I have gotten through reading “testing Electronic Components and several other reports. I am now reading the ART OF SUCCESS IN ELECTRONICS SERVING. I tell you; I have already learned a lots.
J.D

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Hello Jestine,

Frankly, I really need your help regarding how to properly test a power supply of a computer. My sons computer broke down and the repairman told me to replace the power supply. Just the same Im a little poor so I’m just asking if you could lend me some expert advice. I know a little about electronics but I am at a lost about repair of computer power supply.I tried checking it the power supply but it has no voltage output. There is no visible sign of burning. The fuse is still ok. Pls help.

Hi A,
If the power supply have no output and the fuse is working then you need check all of the components in the power side. It could be a power fet, resistor open or even a bad IC. I came across many starts up resistor bad (open circuit) in the primary section of the power supply. Check on all resistors first before you replace the power IC and retest the power supply again.

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Hi Jestine:

Thank you so much for your reply.
May I telll you about my specific problem?
My Dell E173FP 17″ LCD monitor looks great when it starts up. After less than 5 minutes, parts of the screen begin to flash white. Then, within the next 10 minutes the flashing areas expand and flash more frequently, so that eventually the entire screen is white and no longer shows any other color. If I turn the screen off for a couple minutes, it looks great when I turn it on again. But then warms up quickly and begin flashing again. Thinking that some component is overheating, I removed the plastic casing and tried dust-spraying the various components inside, to see if I could cool anything and see if it made any difference in the performance of the screen. No luck. YET. I am concerned about removing the circuit board from the screen part, as it seems there may be some sort of anti-static strips between them, and I don’t know how important they are for the short term. Has anyone been able to resolve a problem like this?

Hi M,
Try check on the high voltage transformer as this model have a common fault of dry joints on those transformer pins. Check other areas fro dry joints too. Hope this helps!

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hi Jestine,

how are u? i am fine. i got one sanaui tv with model no. SV2136i. the problem is vertical.after replacing the ic and some parts in the power supply, the problem is still the same. the size improved after replacing 10uf cap in the power supply.i would appreciate any help you can help me with. thanks

richard

Hi Richard,
If the voltage supply to the vertical IC is sufficient then suspect problem in the corresponding components. Check all of the components in the area especially resistor value. Vertical area resistors are very senstive. A slight changes in the ohms value will hava a big effect on the display. Check also the esr value of the non polarized cap. If you do not have the esr meter then just direct replace the cap and retest. Check also the waveform to the input of the vertical IC as a missing or improper waveform may affect the display. Make sure the vertical yoke coil resistance ohms reading is within the spec value.

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hi jestine thanks for replying to my last post, you say you need the power on the laptop motherboard to test caps etc with my oscilloscope but im worried would this give my oscilloscope a power surge if the caps are charged ? or could i use a function generater with my scope to provide the power to test the componants under test ?

Hi Paul,
When you have a scope, you must know what you want to test and how to test. I would not use my scope to test on the power supply if i’m not familiar with the scope. In you case of the motherboard besides the inverter board, the highest dc voltage that it can go would be about 12 to 18 volts and the scope have the ability to withstand that just incase if you wrongly touch on the wrong point. A scope can set to test till more than a thousand volts. It is not necessary to use function generator if you know hoe to use a scope the right way. Why not get a book about scope from amazon? As it can help you to understand more about scope.

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Hi sir..Good day to you.

i hear about from you, i hope you can help me
w/ my AOC LCD 17″ monitor model:LM720 & model#TFT1780

the problem is “NO DISPLAY” i tried with the CRT monitor ok!
the video card from cpu ok! & LCD power supply ok! but power LED indicates
a “standby mode” no signal from the video card.

Sir, i tried to disassembled the monitor and i got the mainboard of the lcd
to check some “faulty” components using the multitester… but cannot
point the defect. how can i solve this problem…….?

Hi Lito,
If the LCD Monitor power supply is okay and you get a standby mode (RED led) chances is very high the Main board have problem. Check along the VGA connector to the scalar IC to see if there is any diodes shorted to ground especially the red, green blue, vertical and the horizontal signal. Hope this helps!

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Hi B,


I am interested in building my isolation transformer myself after surfing this site: www.raphnet.net/electronique/isolation/isolation_en.php. Is it true that if I am using the isolation transformer when repairing I won’t get electric shock regardless how much the voltage is?

yes it is and the highest voltage it can go is 220 to 240vac

I’ll be using two step down transformer 220 V to 35 V 10 A back to back to get the isolated 220 V as described in that site. My question is do the 35 V side of the step down transformer have polarity? I’ve noticed some transformer winding diagram has a dot in its primary & secondary side. Or could I just connect the four point of 0 & 35V of the two transformers willfully? If the two 35 V AC are not in phase, what is the consequence?

Its and AC voltage thus no polarity. You can just safely follow the diagram.

How if the 35V side of the two transformers aren’t exactly has the same voltage reading?

Maybe different expected voltage (output voltages have tolerances)

Is the output of the isolation transformer still has 3 point: L, N and G or just only two points L and N because now is not earth ground referenced anymore?

It is no more L, N or G. It is just AC VOLTAGE! (TWO WIRES OUTPUT)

A schematic drawing would be much help.

Sorry i do not have isolation schematic. In fact the website shown is already considered a schematic.

Thank you once again.

No problem!

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Hi S,

A Wholesale company wants to give me up to 50 new Large LCD TVs with cracked front screens, are these screen fixable? I haven’t seen the products yet, but I’m assuming that the damage glasses were just a protective layer for the LCD, Is that true?

I’m not sure about LCD TV but if the LCD Monitor glass cracked there is no way to just replace the glass as the glass is not a part of the protective layer.

can I use a regular glass in the place of the damage one?

If you don’t see any liquid spilled i guess that you may replace only the glass.

 

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14 Comments

  1. nowdaygood

    August 21, 2008 at 9:32 pm

    Dear Jestine
    How to delete the scratch on screen lcd monitor ? Because replace a new one very expensive.Example by chemistry method.
    Thank you.

    Likes(0)Dislikes(0)
  2. admin

    August 24, 2008 at 5:19 pm

    Hi,
    As far as i know once the polarized glass had been scratched it would be difficult to repair it. Sorry I've no idea about the chemistry method, well if you have some idea you can try it out and who knows it may solved the problem. Have a good day

    Jestine

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  3. Sam C

    August 29, 2008 at 10:44 pm

    You can fix surface scratch that are visible when lcd is on with Vaseline petroleum jelly which has almost the same optical density as lcd coating. Clean the screen surface, fill the scratch groove with Vaseline and wipe off the excess.

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  4. admin

    August 29, 2008 at 11:11 pm

    Hi Sam,
    What could i say more! Thanks again for your great contribution! Have a good day!

    Jestine

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  5. anil garg

    February 7, 2009 at 8:10 pm

    i have a logix 17h model monitor . its pwm ic ka3842 burns every time when i give power. please advice me.

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  6. admin

    February 8, 2009 at 5:51 pm

    Hi Anil,
    Try remove the power IC and turn on the power and it should have about 15 to 20 vdc. If it shoot up more than the voltage then it will burn the ic. Try to trace back from the supply pin up till the filter capacitor. You may also try direct replace the filter capacitor and bridge rectifier to see if the voltage will back to normal or not.

    JESTINE

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  7. Henk

    March 27, 2009 at 4:13 am

    Hi Sire,
    help please?I have this problem it is a Acer AL1715.
    Come one posts the acer screen then you can see for a split second and the screen goes blank.
    But the led light on the front stays green like there is no problem.
    checked all the capasitors by looking at it if there were blowin up?
    its looks like alright!!!!!
    powersupply board number F1103-D VER:B
    Thankx

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  8. admin

    March 27, 2009 at 11:10 pm

    Hi Henk,
    Suspect a bad backlight because it can cause the display shutdown after few seconds.

    jestine

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  9. 007NIGHTCRAWLER1

    April 24, 2009 at 11:08 pm

    WHEN THE DISPLAY SHUTS DOWN AFTER A MINUTE OR TWO
    IT DISPLAY A MESSAGE SAYING UNSUPPORTED , SO THAT MEANS IT IS LOOKING FOR THE RIGHT DRIVER, I MYSELF HAVEN'T FOUND IT YET BECAUSE,THE NAME OF
    MONITOR IS NOT PRESENT , AND I CANNOT SEEM TO LOCATE IT ON THE INTERNET
    SO THAT I MAY DOWNLOAD THE DRIVER, HELP?

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  10. admin

    April 25, 2009 at 12:00 pm

    Hi Night Crawler,

    May i know what brand is the Monitor?

    Jestine

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  11. majid bagheri

    April 29, 2009 at 6:34 pm

    hi
    how i can add new resolution (for example: 640x448@66hz" to lcd monitor?
    best regards
    majid bagheri

    Likes(0)Dislikes(0)
  12. admin

    April 30, 2009 at 10:09 pm

    Hi Majid,

    The lcd monitor is designed to support on certain resolution and if your resolution is within the lcd monitor spec then it will display it otherwise there is no way to set. You have to check with the lcd monitor manufacturer support center to see if they could provide you with any solution to run on this special type of resolution.

    jestine

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  13. bassam

    May 15, 2009 at 9:52 pm

    i have dell e173fpp i change c5707 but after 10 minutes it s burn plz why???

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  14. admin

    May 16, 2009 at 10:45 am

    Hi Bassam,

    Try check for dry joints in the transformer pins and also the value of the tuning capacitor near the high voltage transformer.

    Jestine

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