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Electronic Repair Questions/Answers & Testimonials Part 3

By Jestine Yong on June 16, 2008

When i press the power buttom the smps works high voltage come up but erratically it does not come up immediately it come up with stages like this tess then silence then tess tess then silence then it come up (tess= high voltage sound ) but then it shutdown smps still work but no high voltage ….along with the strange sound of the high voltage coming up there is a sound of a relay clicking …..occasionally when i switch it on and off some times it work fine the high voltage come up normally and the the picture can be seen …we can brief the failure as intermittent lose of high voltage along with strange sound of high voltage as it trying to come up

Hi W,
If you have the high voltage probe you will clearly see the exact high voltage value (up and down of high voltage). I’ve repaired one before and it was a china made brand. The problem is in the resistor open circuit nearby the h/v oscillator ic. If it use tda4854,4856, 4857 then it is located nearby the output pin 3, 4 and 5. It caused the horizontal output drive waveform to fluctuate. It may not the same in your monitor but at least you will have some ideas where you can start troubleshoot.

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Hi jestine!!!

Thanks a lot for your information, I really appreciate it. Congratullations for your web page, it’s very interesant

Best regards
M.F

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Hi Jestine!! this is Martin, do you have any idea, what’s the NTE replacement for the IC KA431AZ????? I found that the NTE999 is the replacement for the IC UTCTL431, wich is an adjustable precision shunt regulator, and the kA431AZ is a Programmable Shunt Regulator, I think is the same, isn’t?

Martin

Hi Martin,
Yes, both are the same and there is also S431! You can try the replacement number first and if it still doesn’t work then use back the original.

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Dear jestine

Which is the best way to test a faulty IC?
Hi Warren,
Check the supply voltage and test the output with scope.

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Hi Jestine,

I have 2 faulty Sony LCD TVs,One is a KDL-40U2000 40″,the fault is the LED flashes and a switching noise is coming from the PSU.All the correct voltages are coming from the PSU 5v standby 33v,18-22v inverter voltages.The only voltage which is incorrect is the start voltage from PSU to main board,on switch on it goes from 3.3v to 0v and keeps changing between 3.3. and 0v whilst power is there,is this a main board fault,ie processor fault.

The second is KVL-17HR1 WEGA LCD TV,this has power and sound but no picture,it is not a backlight fault as you can see a blank grey/whitish screen.

Any help would be greatly appreciated.

Thx
Hi A,
Thanks for sharing the LCD TV problem. However i could not provide any absolute answer to you due to that i’m more on the LCD Monitor repair. Sometimes i wish that i would get lots of LCD TV for repair but the nature of my repair business is to deal with computer thus do not have the opportunity to touch any LCD TV! As for your first problem it does have similarity with the SAMSUNG LCD Monitor where the start voltage fluctuate between the 0V To 2 Volt. The problem is in the MCU. I confirmed this because i swapped with a known good MCU and it worked!

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i have a problem with my LG TV.The Input of AV do not show when i pluck output of my DVDto it.pls give me a guide on how to solve this problem.Nt
NOTE
when on AV it does not show at all.The screen is always dark.
Thanks and God bless.

Hi Op,
As for the problem, when a screen is always dark this indicates few problem like high voltage shutdown, reduce or mising heater voltage, low or missing G2 voltage from flyback. I suggest that you make sure the TV have the high voltage. You will know that by hearing the high voltage sound rushing out! Once you got the high voltage, the next step is to use digital meter to measure the G2 voltage. It should have about few hundred volts. Next is the heater voltage. If it derived from the flyback then we can’t use our meter to test the voltage due to it is an AC high pulse. Just see the glow in the picture tube under dim room condition. If there is a glow this indicates the heater voltage is functioning and the problem is in somewhere else. Have a great day!

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i came across an isolator in power pack witk 4 legs(2 pairs each for LED and phototransistor).Studies show that one can read this ic havng known its pinout diagram but my question is this”how do one read the transistor in this circuit with only 2pairs with the analogue meter?Although the pinout for this 4legs has 3 legs for s transistor.

Hi D,
The two legs isolator have only the collector and the emitter. You just treat the two legs like the normal bipolar transistor and you can test it with analog multimeter set to X 10 K ohm. It should have only one reading. Some isolator don’t have reading at all-all these depends on the part number.

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“I noticed from one of your article that you start your website in November 2006, but your earliest site was in June 2007, could I still possibly see the earlier site? The electronic repair news in your blog is so precious that it’s a pity if I couldn’t see it. ”

I started the electronicrepairguide website in nov 2006 and launched it on feb10 2007. I don’t get what do you mean by my earliest site in june 2007? I have an old blog which is the http://electronic-repair.blogspot.com

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Typical IC codes in LCD monitor:
Two ICs 78M05 and 78M12 have the same description, are all 5 volts voltage regulator?

78m05 is a 5 v output voltage regulator while the 7m12 is a 12 volt voltage regulator.

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I purchased your book a few months ago and I’ve finally got around to using the knowledge to test some components – in particular a transistor I suspected was faulty. I’m not an expert but I followed your instructions as closely as I could and it appears to be showing signs it is faulty. My problem now is that I have no idea where to find a replacement.The transistor itself has the following markings:————-C1741 |_ |S Q U |————-| | |E C BI have no way of telling what the specifications are, ie Voltage, Amps etc.The transistor is from a hand-held remote control device for my Marantz hi-fi system. The hand-held remote controller has not worked in years hence my attempt to finally troubleshoot it.
I would really appreciate any adivse you can offer to finding a replacement transistor.Hi S.K

According to my databook it is an NPN transistor with the spec of 50v and 0.4 watt. The databook didn’t mention about the ampere. The equivalent part number is 2SC1652. Hope this helps!

Really appreciate your response. How do I go about getting a databook like this in future that gives this level of information?Also now that I know the equivalent part number do I simply go into an electronic shop and ask for this part or is there an online store you would recommend where I can type in this part and be able order online?

Hi S.K,
Got it! It was in mcm electronics at http://www.mcmelectronics.com/product/2SC1741

The databook can be easily get it from any electronic supplier shop and you can just walk in and ask for the part number.

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Hi H,
Sorry again, i do not have the data book for sale. For your information data book should be easily get it from your local electronic supplier. Normally databook will come out every 3 to 4 years once. Sometimes you can key into google the part number and you will easily get the mosfet data. Type in the words like:

xxxxx data
xxxxx data sheet
xxxxx pdf
xxxxx code
etc

xxxx is the semiconductor part numer.

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Sir Yong,

The problem of my 17″LCD is when i turn on the LCD it works in GOOD condition, But after an hour when i turn of and turn on again it does not work , i mean that The LCD turn into BLACK state except the NO SIGNAL CABLE DETECTED. and please i need help and it is my honor and a great THANKS to you Sir……

Hi Fern,
Samsung LCD Monitor have a common fault of failure in the MCU. It causes lots of problem like display shutdown intermittently, no display, power LED deosn’t light up, OSD running across the screen and etc. Have a good day!

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I read one of your articles on Repairing Samsung 713N LCD monitors with SE7889-LF IC problem.

Sir, at the last end of your article you said “I could not pinpoint to you the exact faulty component”

At moment my company has about 20 of that and we have 5 having OSD of check signal cable problem.
Please is there any way to repair this done changing the main board?

Hi T,
In your case it is confirmed the mainboard have problem . This is due to a bad MCU and you need to replace the whole mainboard.

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Hello Mr.Yong
My name is Randy and a few days ago I purchased your ebook testing electronics. First of all I’d like to say it’s a great purchase I’ve made with so much useful information and thank you. I’ve been interested in electronics since I was a kid and am slowly getting better at it. I’m hoping that by rereading this ebook I’ll finally be able to figure out a tv I’ve been trying to fix for quite some time without success. Maybe you’ve had the same sort of problem I’m having. It’s a Samsung model TXR2735X chassis KS7A. When I was first given the set it would shut off every 15 minutes. A guy on the Techlore website told me these sets were known for component IC801S failing (STRX6750) I replaced this piece and now my set seems to be stuck in a sort of protection mode with the relay constantly clicking and the led flashing non stop. Ever had this problem or have a suggestion? Once again thanks for the great knowlege in you ebook!

Hi Randy,
Glad that you like my ebook. First try to put back the original IC and power it “On” again to see if you get back the original problem (shutdown after 15 minutes). Before that what do you mean by shut off. Is the display shut off with power led still “On” or the power LED totally goes off? Sometimes a secondary provlem could cause power to goes off. To isolate this problem you have to connect a 100 watt bulb across the B+ line to ground. You have to remove one of the component path to flyback pin. Now power ‘On” if the power still shutdown that means only the smps side have problem. Check all e-caps for high esr value and also the components near the optoisolator ic (if have). Please keep me update so that i can further guide you. Have a good day!

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Hello!

Thanks for your interest on my behalf.

I purchased your books to gain a better knowledge on understanding how electrical components work to help me to repair problem components.

I was recently given a TV DVD?VRC combo (Magnavox Model 20MC4304/17)…… When you power it up it works fine for the first 10 seconds then shuts off. I do not have any schematics on this TV so I’m having trouble figuring out were to start. I would seem to be a power problem but just not sure.

I’m very new to this field of expertise so any information that you might have to help me along would be greatly appreciated.

Thanks again for your interest in me and helping me to gain so knowledge in this field.

Hi L,
Thanks for the support on my book. As for the tv problem, it can be in the power section or in the secondary section. First thing you need to do is to separate out the section. Remove one of the component (after the secondary diode and filter cap) along the B+ voltage (about 110vdc) and connect a 100 watt bulb between the line to cold ground. Try power “on” and see if the smps still shut down or not by measuring the output voltages. If it still shutdown then most probably is the smps fault and if the light bulb “On” and did not shutdown then most probably something shorted at the other side if circuit like shorted Horizontal output transistor, FLYBACK TRANSFORMER or even shorted yoke coil. The shorted primary winding and yoke coil can only be test with flyback/coil tester.

If you have the esr meter, you could scan through all e-caps in the primary and filter caps in the secondary as these caps could also cause the Tv to shut off.

Click here for some very good repair tips from sencore at

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

http://www.scribd.com/doc/2950481/TT203-Understanding-Switch-Mode-Power-Suplies

If you have other questions please do email me again and please let me know how is your outcome. Have a great day!

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One Comment

Kent

June 16, 2008 at 11:34 pm

Hi,
Regarding the lcd tv problem, i think the led light flashes have give us an answer. Please look carefully on how your power led light flashes or blinking. It will let you know which part are defective.

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