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Electronics Repair Questions/Answers and Testimonials- Part 80

By on June 10, 2011

Hi Jestine, 

I’m glad to inform you that I have successfully downloaded your EBook report on Electronic repair and Testing Electronic components. 

I have a basic knowledge on electronics and with your EBook on electronics it will really help me get to understand more on components and repair. Also your simple explanations and English is very easy to understand. 

You are great. 

Best Regards,


Lae,Papua New Guinea


Hello Jestine,

I hope you are well and also your family are ok also.

Firstly I would like to thank you for all the help you give to people who are learnig about electronic repairs just like me, You always send reply to emails on help.

Jestine congratulations on your new web site, I joined yesterday and it is fantastic, it will very much help all people and especially people like me who are just starting with electronic repairs.

Fantastic site.

I hope one day I can be like you, you are a great guy Jestine.

Alan (England)


Hi Jestine,

I must first of all say thank you, and then a very big CONGRATULATION, you are not only a teacher but a very good role model,
Jestine, your dedication to educate and help people in this profession is .is rowing more and more, so many people like me have been really benefitting from your knowledge.

I wish you all the best in your future endeavours.

Thank you again and have a nice day 



I bought a few weeks ago your excellent book "LCD Monitor Repair" and thanks to your skill and experience I’ve already repaired 8 LCD monitors (SAMSUNG, LG,
ACER, HANN’S G). Each time, the problem was faulty capacitors. For the same problem, I repaired 2 SMC network switch’s PSU. And I’m not a professional in
electronic science: I just work in a hot line service in french state administration !

Thank you a lot Mr YONG for sharing your professional experience with so many people !

Best regards

Gilles, from France


Hi Jestine,

Your LCD Monitor repair guide I bought was so great. Its like your teaching beside me. Very brief and easy to understand.

Thanks and God bless.



Hi Justine

I’ve a problem with my tv,when i turn it on there is a low sound that
it does turn on but it seems the power is not enough.A big cap with
400v 150uF looks like it got damaged and it has this ic that am not
familiar with la78040.i want to troubleshoot it.i dnt know where to
start help.

T.P Theko
South Africa

HI Patrick,
In that case i suggest that you check all components in the primary section. Make sure also no shorted diode in the secondary section. If all components check to be good then directly replace the power ic and retest.



HI Boling, 

This monitor led indicator is steady lit, but the relay is pulsating. After dismantling, found there were some dry joints and I had resoldered all of them, all the e-caps esr were OK. 

To make sure, I had tested it with isolation method, found the bulb was also pulsating but now the relay was steady ON, and the time interval to light to bulb after a minute pulsating become longer and finally it took much time to light the bulb. When the bulb was off, I tried to check some secondary voltages, found a point is still 187V ( buck circuit ). 

Do you see there is some problem that I still oversee it?

Relay pulsating could be some thing had shorted in the secondary side, primary side component problem that had caused pulsating voltages or the cpu that send the signal to the transistor to drive the relay pulsate.  I suggest that you isolate the problem first by removing the B+ coil and connect the bulb and see if it still pulsating or not.




Carbon film resistors need to have one lead removed to properly test ohm’s but what about smd type resistors. Can they also be in parallel in circuit and need to be removed to properly test?

HI Dave,

If you check on board and you got the value quite close then no need to remove the smd resistor out otherwise you need to remove it for accuracy testing.




hello Jestine is it possible to restore a crt which has other defects rather than a faulty heater element.

HI Sammy,

Try this link;



HI Boling,

The 187 V is the voltage just after a diode cathode in the secondary circuit, so it is before the B+ FET.

If it is a buck circuit the voltage will be generally high. What is the filter cap voltage rating of B+ line? If it is rated as 200 volt then 187 is too high. If it is rated as 250volt then 187v is normal. What about other voltages like 6.3v, 12 v or even 15 volt? 

By the way, when I checked the primary SMPS by the Blue ring meter, ir only showed 6 led lit ( up to the first green led only ), is this OK?

Yes it is good as different model will have different reading. Some could have even 4 to 5 LED lit.

I came across a pulsating problem before in a LG 700 Monitor and the cause was due to 7805 and 7812 voltage regulator that have intermittent problem. These IC brokedown when under full load and it took me also a month to locate such problem. If your monitor is using these ICs then directly replace and retest.



HI Selim,

I have a Thomson LCD TV with the following PSU: JSK4338-007A (I’ve attached the schematics).

My problem is that as soon as I turn on the TV the standby LED goes on for a second and then goes off (same thing happens when I unplug the TV). When testing the secondary outputs, I have no power on the 12/18/24 Volts but have power on the other output (I’m guessing the standby output) with 5 Volts.

Yes you are right.

I’ve checked the B+ error detection line but couldn’t find anything obvious there. Hence I exchanged all three opto-couplers – still no avail. Transformers show no issues when checking with the Ringtester. Also all main caps tested fine with the ESR tester.


What I did find is that R30 and R8 (both 4.7 Ohm resistors, located on the hot side close to the opto-coupler 3) showed a reading of 5.2 Ohms (but they only have a 1% tolerance). Now, I haven’t got the parts yet (should get them today) but I’m wondering if I’m completely off the track or if that will solve my problem.

You need to try it out because components located in the opto ic area are consider critical parts and the value has to be the same if possible.

If the resistors do not solve my problem, I’m quite lost and desperate, hence this mail to you.

What else could be the cause of the LED blinking up and dying after turning the TV on and/or off?? Any ideas are absolutely welcome!!

The moment you power it on the cpu will get the 5 volt. When turning on the tv by pressing either the remote or the power button in tv should cause QS3 to conduct and this will trigger the IC 3A and IC 3B which will turn on the main power supply and producing all the necessary output 12/18/24v . If the QS3 does not turn on either the surrounding circuit have problem or the cpu is bad. If QS3 could be turned on then check all the corresponding components that is related to IC3B.



Hi jestine,
I purchased your book "lcd monitor repair"through my elder brother resident
in France . I have been into repairs for the past 10yrs and it was becoming
frustrating and I was about leaving the job until I came across your book. After
reading it, I changed my mind . To me it is a gold mine in my hands.Soon, my brother will be making some purchases on my behalf.

May God keep for us,
Stanley from Nigeria.


Hello Jestine,
   Could you help me to become familiar and categorize between the IC’s, triac, fet, transistor and others thru their part numbers. Thanks for the support.

HI Fernan,
Search the component datasheet and you will know if it belong to which component category.


HI Uday,

I just want to know both LCD and LED monitors are same or different in circuit design.

Almost the same except that the LED did not use high voltage transformer to drive the CCFL lamp. It uses a LED driver circuit to drive the LED lamps.

And do I need to purchase CRO and function generator for service or not please tell me sir.

Yes you need a scope for troubleshooting and you do not need a function generator. Get a scope that have at least 100mhz.


HI Russ, 

Need some help again.  And thanks for any insights.

No problem 

This is a security 14" CRT monitor.  The kinds where the put four cameras into it and you can watch and record what is going on. 

It was completely dead.  I found a shorted transistor in the primary and replaced it.  Now I get the following.  No high voltage, 120VDC at the HOT, which is correct according to the a voltage marking near the flyback.    No signal, or oscillation going into the HOT or going into the driver for the HOT.  The signal comes from a TDA8834 which is a I2C controlled chip and I don’t know what to look for to see if it is not getting a input signal that it needs to produce a HOT output. But no signal seems to be coming from pin 40 the HORTZ driver.  It is getting the correct 8VDC.

Did you check the supply voltage? 

On one of the secondary lines 9.8VDC instead of 12VDC.

Try remove the load/break the circuit connection to see if the 12 volt would rise back or not. 

I am a little confused on why I am getting a correct B+ 120VDC but I am getting a low 12VDC (9.8VDC)   I have checked every component in that 12V line and they are all good.  If there was a problem with the primary regulating the outputs wouldn’t all of the voltages be low?  Not just the 12 volt line?   If I am getting a low 12V line doesn’t that have to point to a problem in that line only?

  I am unsure of what the other secondary voltages should be because I have no schematic. I do know that the 12V is 12 because it goes to a secondary board and when I apply 12 volts to that board it works but does not work at 9.8V. 

Any thoughts on this?

Try remove the load/break the circuit connection to see if the 12 volt would rise back or not.



If I were to unload a secondary voltage by removing the diode and then if I measure the AC at transformer.  Shouldn’t I be able to calculate what the secondary voltage should be with some math?  And wouldn’t that tell me if there was a problem if those numbers didn’t match?

No, the ac can’t be measured that way because it is a high pulse ac and your meter will give you a false reading. I suggest that you remove the load/ circuit connection in downstream and see if the voltage will rise back or not.

One more thing i would like to share about circuit design that use I2C bus is that since all the ICs are connected and communicate using I2C bus then if one of the ic have problem it will affect other ic as well. To make it simple, i came across a 17" crt monitor where there was no output signal from the h/v oscillator ic. After replacing the video preamp ic (tda4884 if I’m not mistaken) the high voltage came back. The reason for it because one of the SDL/SCA pin in the video IC have shorted causing the h/v oscillator to malfunction eventhough the h/v ic is still getting a good supply input. 

You have always seemed to reply to my emails very quickly which I really appreciate. 

You are welcome! But sometimes it depends also on how many email i receive in a day. Usually after sending out my monthly repair newsletter i will get hundreds of email and this will take sometime to reply. And if i have repair course "On" i might be delaying in responding email.

I am sure you are busy but if you did do something where you could help by email perhaps have a higher cost for quick responses and another cost for replies that might take a while. 

Thanks for the suggestion but at current moment  I’m still able to manage the time for support.

Or maybe a repair forum.  You must have enough people who are interested.   

I have thought of that but again it needs dedicated and trusted moderators to manage the forum from different part of the world.



HI Willem,

Hi Jestine can you please help me I’ve attached a photo of the problem, it is a Tedelex 51 cm TV. The only thing that happen if you put it on is that it is displaying a white screen with black vertical bars at each side. Nothing else is displayed. There is no OSD. The volts on the CRT board is 83V for Red, 83V for Blue and 84V for Green. The supply voltage is 179V. I am not at all sure where to look for this problem. Thank you in advance.

Some tv have G1 and some do not have. If your tv have the g1 voltage make sure it is not zero volt at the crt otherwise it will become bright. Check also that the G2 voltage is not too high. Keep me update on this repair.



Hi Jestine!

I’m struggling to find supplier for backlight in South Africa! Is there an on-line shop I can purchase from?

HI Riaan,

Try this link:



good day sir Jestine! 

I finally got your E-book..I almost finished reading along the way I have repair Computer Motherboard, Flash Drive and refresh from the very important basics of electrnics, I found your book very informative. I finished Bachelor in Electronics & Communication Engineering but I found it almost theories, As I landed this passion in repairing is enhance & developed.  I am planning now to put up a small electronics shop here in my hometown. Thank you sir for this book…I’m planning to have all your books for my reference in the near future. 

Thank you & God Bless. 

Lito Malinis

Tacurong City, Philippines


ah ok! tnx…. but commonly defective is the transformer for the backlight, was that right? i can see the physical appearance of the transformer that its already burnt.. but i dont any other transformer to replace… its not available in electronics stores

HI Baddy,

In certain model it is common to have bad transformer. I suggest that you compare with the top or bottom transformer in term of ohm reading. Any different reading means the transformer is at fault.  Try email Luca at to see if he has the transformer or not. Luca is from Italy.




I bought a 32 inch TV and within 6 months it stop working. I believe that it
has something to do with the power supply. Actually it was on and I cut it
off for about an hour and when I put on back the power it did not come on
since. What do you suggest? The info is

LC-32D4 3U
S/N 710818603.


HI Glen,

If the power led is totally not lighted up then most probably the power supply board is the problem. Try open it up and measure the output to see if the power supply working or not as sometime a bad mainboard may also cause such problem because the power led signal is coming from the mainboard.



HI Jeffries,

Hi Jestine, thank you for the newsletter u sent me, it surely shows how much you are dedicated to bring up new skilled young technicians. I surely appreciate. Now Jestine what i can i do i have the theoritical knowledge of locating fault stage and the posible faulty device in a TV set but my major problem is how to locate them in the circuit board. For example a set having only a bright horizontal line traced on the screen, i know that the faulty stages may be the vertical sweep or vertical deflection coil but i dont know how to locate the vertical sweep on the circuit board, can you please help me with the practical skills on troubleshooting & locating in the board for a TV set. Thank you, have a nice day. Jeffries, Kenya.

I suggest that you download any tv schematic and start analyzing it. If you found an ic in the schematic then look for the ic datasheet as it did show you how the ic look like, pin out description, supply voltage and etc. This will help in your troubleshooting job.



Dear Sir,what are the feedback circuits to make crt tv to change over to
standby position while working, Sony kv-G21P2 model.


There is no feedback circuit on this. Just press the remote control and the CPU will stop sending the signal to either a relay circuit or optoisolator circuit to cause it to go into stand by mode. However, if there is a problem with the cpu, eeprom, shorted component like HOT and it will also go back to standby mode.



The power supply goes into protect but when I tested solid state devices, caps etc. nothing appears to be shorted or destroyed.

I don’t know if you can bypass the power supply protection circuitry to try to troubleshoot. I am assuming that you are troubleshooting 

and testing components with no power. It is a pc power supply that I am trying to repair to gain experience and knowledge. Any help will be appreciated. Thank you so much.

Hi Sal,

It is not easy to disable it as there is limited sources in the power supply schematic . There are thousands of design and it will take a lot of time just to locate and analyze the protection circuitry. Sometimes it is good to have protection circuit to kick in because if there is a problem the power supply will shutdown otherwise overcurrent/overvoltage could destroy or even burn the components.





Do u have some lessons on how I can repair my own TV.  My Sony 40XBR800 won’t turn ON, giving me 7 blinks on the red LED.  Website indicate that this model is very common on this problem by replacing the power supply IC chips.  After doing that, it still not turning ON.  I asked the website:, spoke to 2 TV tech. and they’re just giving me the run-around.  Very frustrated.  Please advise.  Thanks.

Hi ,


Sony design is a little bit different from other design. If there is a problem with it the power led will blink and this indicate there is a problem. The problem is that we do not own all the service manual of Sony thus we can’t pinpoint directly where the problem is. Sorted in one of the ic like vertical ic also could cause blinking problem. However, you can use some steps to isolate the problem by following the link below:

If all the voltages are good and stable then possible the cpu or the eeprom may have problem.



there are so many different LCD Monitors in the market. And at my advanced age I surely not becoming a repair spezialist.
I would just like to get my Acer AL1715 back into operation. And my main stumbling block is how to dismantle it without distroing the casing.
Its elctroni problem must be its power supply: after switching on the power comes on but then cyclically disappears. I had such a problem with a 5V/12V power supply of an external WD drive. It was just the DC capacitor on the mains connected switching power supply, which had to be replaced. Unfortunatly not having the schematic of this power supply I cannot clearly indicate its position to any interested party.

HI Hanns,

Try remove the base first as in certain mode there is a cover covering the screw inside. Then you need to peel from the below casing with a flat metal (please do not use test pen as this will leave a mark on it) Once opened you can now try peel at the side.



this capacitor located at horizontal section of sharp tv. a safety capacitor value 672 or 6.7 nf and below 1.5kph. is 1.5 equals to 1500 volts? Thank you sir.


Hi Zed,

Yes it is 1500 volt.



Hi jestine how are you , I wanted to thank you for the book LCD monitors, cause I already fixed one monitor, very good book, jestine I also have a question for you, what’s the difference between a LCD monitor and a LCD tv?, is it just that the LCD tv has a tuner, the rest of the circuits inside are pretty much the same?, thanks, and congratulations for the website, so, the website it’s gonna be even better, kool.

Hi Herberto,

Yes they have extra circuit like the tuner and audio but nowadays all circuit already built into one piece of mainboard. The recent LCD TV 24 INCH have the same type of board like lcd monitor except that the boards are much bigger and have more backlights. Of course there is a built in tuner in the mainboard.



Hi! Jestine!  I have got a circuit diagram of  2km FM transimitter,But i dnt knw those capacitors voltage carried according to the diagram (uF) seen,can you help me to determine the volts in those capacitor(see attached image of circuit diagram)

Hi Amarino,

Since the supply voltage is between 9 to 24 volt, for electrolytic capacitor you can use a 35 volt cap and for non polar you can use a 50 volt cap.



Hi Eric,

Hi Jestine How are you? Hope all iis well with you.

I’m fine thank you.

I am trying to repair my  Optiquest Q 71 Monitor. Whenever power is applied the monitor starts then suddenly stops and produces a TICK TOCK sound in a square looking component just next to the big filter capacitor  the green led lights then fades with the ticking sound.

You mean the square yellow component? That is a power transformer. But tick tick sound usually came from the flyback.

The led does not turn amber as before but just bright green and dull green. What could be the cause of this ticking sound that is preventing the monitor from coming up? Your usual professional help is awaited. Thank you as always. (The green led blinks as in a motorcar indicator lamp)

It can be something shorted like HOT, FLYBACK or even horizontal yoke coil. You need to make sure that the output voltages from the power supply did not fluctuate.



Hi Jestine,

Thank you very much for your help.

After removing the filter cap. C201, the output was good and I tested, the display came up. I was afraid without filter cap. may damage the circuit, I didn’t keep power on for too long.

C211 to C214 are all ok and as I heard some switch like noice when keeped power on the power board, I even changed IC202. The C206 is a very tiny and looked perfect cap, but the problem is caused by him. After change the c206 (22uf 50v), my 22′ monitor gets back to work. It’s interest as by eye nobody will think such a perfect looking one cause the problem. If I have a ESR meter, trouble shooting should become some more simple.

Again thanks a lot!

Best regards!

Hi Charley,

Congratulation- You need to invest in ESR meter if you want your troubleshooting job easy.

Have a good day.



HI Boling, 

I congratulate you on your new website and hope all fellow repairmen could learn something new from the site.

Thanks and i hope you can participate in the website too.  

These days I am still repairing junk AOC 15” CRT monitor which I bought from a factory last month. One of them is having this problem, when I switch the set on after the routine checking, there was a volley of explosion heard, the display had not come up yet and the led indicator is steady green.. I didn’t notice clearly where was the explosion from, but once I saw a spark beneath the convergence board lid. To prevent from further problem I immediately switch the set off. Why this kind of explosion didn’t cause any smoke built?

I believe is the spark from the yoke coil to the picture tube aquadaq.

Is it true if I leave the set on longer there would also give off smoke?

I can’t confirm that but if there is a sound then one should off it. 

I recheck the yoke coil with the blue ring tester and the result is OK. Why don’t we ever need to check the convergence board?

Convergence board rarely give problem. The problem i had with the convergence board was dry joints causing convergence out.

Is the yoke coil test result OK with blue ring tester means the convergence board would also be OK?

Both are different thus if the yoke coil check to be good not necessary the convergence board is good.

I really don’t know how to check the convergence board.

There is not much component to check on the board and the board rarely have problem. 

I also took out the flyback to see if there is some hairline crack but found nothing bad.


What is causing the series of explosion heard once the set is switched on? Could it be a bad picture tube? 

It can be from the high voltage too high (you can test it with your high voltage probe) or the yoke coil have problem.



Hi Carmelito,

how are you..

I’m fine thank you.

please give me some advise about toroidal coil….

im currently repairing LCD and i found burnt toroidal coil….

i send you in the pic please see the attachment…

this coil have no specification or maker…

how to deal with this toroidal coil?

If this coil is located in the ac supply input then it can be tested using ohm meter. This coil can be easily replaced with another similar coil from another set.



Hi Gary,

i have a problem with a 15" aoc monitor… when i use, 100 light bulb in the b+ section all the output voltage are ok… when i put back the b+ coil only 72 volt to secondary up to b+ of fbt… i change all the electrolitic capacitor and diode uf5402.. on the line of b+…. i have the same monitor here.. the B+ is 145 volt… plz help me thnk u

i open it 4 a while when i change the capacitor but after a few minutes it goes off.. and the voltage of the B+ of fbt is goes to 72 volt again… the fbt is ok i use bluering tester… hot is ok 2… plz help me mr yong… thnk u very much…

It could be the horizontal yoke coil shorted or the internal capacitor shorted. Please refer to the link below:






  1. Mark

    August 14, 2012 at 1:12 pm

    Hi! What could be wrong with a10 year old AIWA CRT TV when the settings keeps on changing automatically. Sometimes it changes the audio setting, sometimes the color and sometimes the channel settings. The OSD appears on the screen when the settings are changing. Could it  be due to defective capacitors, EEPROM..?

    • Jestine Yong

      August 14, 2012 at 8:51 pm

      Hi Mark,

      Chances is high on bad data in eeprom. Before that make sure the eeprom is getting the right supply voltage (5 volt).



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