Electronic Repair Questions/Answers And Testimonials Part 10
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.
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!
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?
Greetings thanks’ a lot for your site 🙂
I went to
It would be a waste to throw away a 19″ LCD if I can’t get the faulty component parts?
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.
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
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
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.
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
When working with some electronic boards I come across some LEDS labelled Tx and Rx, what do Tx and Rx stand for?
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.
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 :
Ground in device that does not use 3 pin power plugs.
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!
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.
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!
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
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.
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.
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.
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?
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!
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
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.
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 ?
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.
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…….?
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!
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.
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.