Electronic Repair Questions/Answers and Testimonials- Part 49
I just downloaded the eBook, and had the first successfully repair of LCD monitor.
Thank You and
thank you Jestine
Just finished registering for my diploma today I got a scholarship and all the credit goes to you for giving me free education I would not have done it without your help.
much blessings and keep up the good work.
your book has taught me what i have not learnt in my 5-6 years of attending a tertiary institution.kudoooooooooooooooooooos.
I am called kaggwa
I am technician in a poor country called
fellows. I repair Tvs, DVDs,monitors,LCDs are there in our country but are taken to improved and well facilitated workshops in the city.I have repaired one succesfully,it had a power failire this was before reading you repair guides this prompted to look for information about this seeming excellent new tv that everybody desires to have in his home.
Unfortunately we have not yet penetrated that market but we hope one as time passes and things change for the better we will expand.
i have written to you this mail mr. yong just to thank you for the repair articles you send to us as free repair guides if i dont thank you i would have cheated my own soul,for he who doesnot thank man will not be even thakfull after God(ALLAH) has given him either life, wealth,or anything good in this earthly life.
Thank you again for this very interesting news letter. The feed back is a very important subject, and it was fantastic that you brought it up.
Take care and have a nice day
.I wonder if you could help me.I have been repairing TV sets for the past four years on part time basis,but one problem beats me all the time.
I am currently working on a dead Tv set(Telefunken old model),its problem being overheating fusable (big) resistors on the primary power supply section.
Even if i eliminate the flyback,the problem remains the same.
On checking B+ it is not reaching the flyback.
Could the problem be on the socondary side? Please help
About myself,I have a qualification in electronics and currently pursuing a course in Telecommunications.
I guess you may need to test all components in the primary side. Sometimes a bad primary winding coil may contribute to such problem. Try this link to isolate the problem:
Have a good day!
I am trying to repair a Compaq 17″ MV 720 monitor.
I can’t seem to find a connection of the primary of the line transformer to the B+ supply.
You mean you can’t find the primary winding of the flyback transformer? Look for the B+ supply input and the collector pin of HOT.
That two points are the primary winding.
I have a background’in computers and I’d like to learn how to repair LCD monitor/TV, but My question is… Is it really worth it?
Once you know how to repair electronics, you will have many choices of repair field you want to choose. It is not necessary have to be in consumer products electronics repair. It is worth it to equipped yourself for your future.
Is it a good business?
It depends on how you run your business.
I need to know because nowadays one can buy an LCD monitor for as low as $100. In the other hand if you ever need to repair one, just the inverter or back light could cost you $150, so where is the logic here.
Most of the time, the backlight, inverter and power supply circuit can be repaired and the cost is very low. You will make some profit if you constantly get lots of Monitor for repair. As mentioned above, it is not necessary have to make money from this field alone.
I love Electronics man, for sure I think you can notice the passion in me.
I have a question for u.
1.Is the s2000af equivalent to st8812fx?
You can try to replace the St8812fx with S2000af but with one condition. After power On make sure the HOT do not get hot after a while otherwise it may blow the HOT. Before replace make sure all the corresponding components are good.
2. A Sinotec TV is switching on, screen becomes bright with horizontal lines. if i adjust the screen switch on the EHT, it switches on and off. Changed some resistors and caps around the EHT but no change. What could be the cause?
Adjusting the EHT voltage too high will cause the screen to switch on and off. Try lower it down the voltage and check the Vertical output IC and surrounding circuit. Look for the blanking signal in the IC and trace from there.
Hello! Jestine, it has been el pleasure to know you. you dont know the
important tha has been to know you by internet.
I have learn many things by your information and tip repairing.
Thank you very, very much. for all your help.
Thanks for the repair newsletter you gave me. I learn another repair guide which cannot be learn in school. Thanks.
I encountred a problem with a monitor that has a good picture but there is a thick horizontal black line at the center and from the center ar thin black lines that are coninuosly moving from the center to bottom. The brndmake of the monitor is an AOC model 5 E n.
What can be the source of this problem?
It could be a bad filetr cap at the output of power supply.
Hi Brother Jestine,
How are U? quite sometime no email to you because busy , Jestine I remember once a member ask you in Shenzen the place where you can get Laptop spare parts right, so my brother ask me to ask you the place, as he will be going to shenzen.
Go to HUA QIANG BEI (SEG tower means SAI GER Ta Xia). The building is directly opposite across the road of Sai ger building. Go to 3rd or 4th floor and he will see lots of laptop repair technicians and parts too.
Thanks for the address of the Laptop Spares place. Today I like to ask you a Q, a
Perhaps design or quality problem with the diode.
hello Jestine Good morning!!!
it’s morning here at
By the way I have checked the rectifier and its shorted so I replaced it, when I try to power it on the indicator light only blinks but no display..
Usually when the rectifier shorted the fuse will blow. Okay, have you test all the output voltages from the SMPS to see if it stable or not. If it is stable then suspect a bad mainboard. If it is fluctuating then suspect either the power supply itseff or the inverter board have problem. You may need to test out all the components in the power side.
I’ve been repairing CRT monitor for about a year, and one of my customer would like me to repair his CRT TV.
I know you had repaired some CRT TVs from your blog. Do you think it’s easy for a monitor repairman to repair a CRT TV?
It should not be a problem as CRT Monitor have many similarity with CRT TV.
What do you think? I know from the HOT datasheet, some TV are using the same HOT as monitor, is that true?
Yes it is like BU2508AF and etc.
How about the ICs, are they using the same for TV? I’d like to learn something from your experience.
No it is different.
I know that TV has tuner and IF circuit, what are the other circuits that monitor doesn’t have?
Audio/sound circuit .
Venturing into this field means you have to start from the basic of learning TV repair. Get books and visit TV repair forum will be good for you.
thanks for the 2010 newsletter on Feedback.i am going thru.
You are welcome!
While reading your newsletter,I remembered the I bought An LG CRT monitor with cut signal cable.It was cheep as it had no signal cable.I wanted to buy and fix the cable.
To my greatest surprise,the cable I joined to the short cord left at the back of the monitor, though has the same number of wires as the short cord,it refused to receive signal.
I found out that, two wires in the cord I joined to that of the monitor had different colours.
The only option now is to look for signal cable from a damaged LG monitor.
Is there a way you can help me out?
You have to get back the original cable or compare with a good LCD Monitor. Different Monitor manufacturers produce different colors for different signals. The standard color signals are the RED, GREEN and BLUE wire.
I am thinking of taking picture of the short cable left at the back of the monitor to you so the you may trace where to connect the wires in the signal cable I wish to join to the system unit.
Looking forward to hearing from U.
Try this link:
How youdoing,i hope everything is going well.
Yes I”m fine thank you.
Jestine,i need your help on three monitor problems that i tried to repair but i could not.
Here is their model and problems:
No.1-SAMSUG syncromaster Model no.700IFT.This monitor problem is one horizontal line,the line is not sharp narrowline it is little wide and the desplay is shown.
Check the vertical section-check for supply voltage, corresponding components and replace the vertical output IC and retest.
No.2-PANASONIC MONSTOR,Model no.P70.This monitor problem is color there is only one strog red color.
Compare the red circuit with the green and blue circuit in term of voltage and signal. Any different in the voltage and signal is the clue for you to trace from the circuit point.
No3.-Aopen,Model No.A50V.This monitor problem is power,there is no stundby light,no rely clicking and no B+ voltage to the HOT,but when i measure in the secondury output i fuond three vltages that they do not go further from the secondury filter capacitor,their rate is 32DCV,10DCV AND 9DCV.THANKYOU!
It could be primary power side problem or the secondary side components shorted that had pulled down the voltage. please visit this link to isolate the problem.
Thank you so much. I have question, What is the function of an IC
SE130 (3 pins) Can you give me its pinouts. Thank you so much
Here is the link:
Second problem , what causes when a relay in a power supply wont
work or power pilot light wont light, Your help would be a great help
and much appreciated. Happy Valentine’s Day in advance and more
Power side problem and you need to test out all the components in it. It can be a shorted diode, transistor, open resistor, bad cap and etc.
Happy Valentine’s day!
I have this lcd screen 19 inches. I plug it in the ac outlet and it will not come right away. it takes about ten minutes to start. once it is started..it will go very normal. I replaced all the capacitors in it but still the same problem. any ideas? thanks
Sometimes the power IC could cause such problem. Try replace and retest.
I have a odd question for you. I have tried replacing back
lights in 17″ pannells up untill today with no luck but
my competion from
caps on motherboards and fix lcds gave me a 17″ Phillips
on Saturday to fix for him. I did find 1 popped cap right
where the back lights plugged in,replaced it and tested
it ,came on and showed screen for about 1 min then black
so I decided to take apart the pannell and found the top
light was burnt after carefully getting it apart and replaced
it with a good one. I then pieced it back together and the pannel now works fine. My question even though this my first successfull one how come whole screen goes black when only one back light is burnt out. Have you any
answers to that one. Now that I got 1 working nicely
I think I will attempt more tries at it.
It is because of feedback circuit that it sense something that had gone wrong with the backlight thus shuting down the light thus it will look black. Hope you will have more success!
i have gone through the smps repair and the testing electronic components books, and i found them as the best that have ever been written on both electronic theoretical basics and practical troubleshooting. indeed they are books that every electronic repair technician must have. thanks for those wonderful and useful work.
Please i have three questions:
1. in the isolation method, before conneting the bulb in the B+ line, should other secondary diodes be left intact in the circuit? if so if there is fault in those other secondary loads, wont it cause the bulb to go off or blink making one to wrongfully suspect the smps?
Yes all the secondary diodes have to be left intact otherwise if you remove it the SMPS will not work. Usually only one of the secondary section that have problem and i have not seen two different sections shorted together at the same time.
2. in the stand-alone power unit, those ones that require a load to run, if one uses a good mainboard to test it, should the power unit has a serious fault like higher than normal output voltages, wont that affect or burn components on the main board?
If you are using back the same board then it should not be a problem. If you use other type of mainboard for example when you repair the printer stand alone type of power supply and you connect it to LCD TV mainboard then it will not work and may burn the component. Once you have the original mainboard then you are safe.
3. if one decides to install a stand-alone smps to a CRT TV or monitor so as to by-pass the irrepairable on-board smps what are the technical procedures and disadvantages?
It would be difficult to achieve because usually the CRT TV do not have a standard output voltages from the SMPS. Some set could have 4 outputs and some may have 6 outputs. Besides, the feeback pulse signal from the flyback transformer have to be fedback to the SMPS circuit otherwise the display will look wavy. The stand alone type of power supply do not have such circuit to take in the pulse signal.
However, it can be done on LCD Monitor because generally the output from the SMPS are quite standard of 12v and 5 volt.
Hello there , please can you help with this technical question ? , yesterday a electronic teacher in the London Electronic College told me that in reality the PSU dont really need that much of airflow to cool the inside of the PSU , the main function of the fan installed inside the PSU is to cool all the other components inside the computer and therefore is possible to remove the fan of the PSU if there are other fans to cool the other components inside the computer , I was complaining about such statement explaining to the teacher that if there is no fan inside the PSU , the heatsink inside the PSU need to be much much bigger to compensate the lack of a fan inside the PSU , can you please tell me your opinion about this question ? , thank you
regards Enrico Napolitano
It is better to have a fan in PSU. Not only it need to cool down the heatsink, it also need to cool down the power transformer. In modern LCD Monitor power supply that do not have fan, i found that lots of capacitors bulged due to heat. The power supply covered by a metal shielding thus it is even harder for hot air to be removed.
by the way, about my sony tv, big filter capacitor is good! i check smps primary winding with ring tester, 8 leds lit.
pwr supply board is separate, when i switch on the pwr supply without load, 470ohm resistor burned besides the posistor, i change the resistor but same thing happen. is posistor have problem?
Did you connect the degauss cable?
smps x’former have regulator ic STR-S5941 but all voltage drop at all output diodes and i change already the regulator ic but still humming sound coming from the smps x’former.
Have you check all components and isolate the power supply?
when checking HOT onboard in crt monitor is the same also in checking on crt tv?
Yes it is the same. Try isolate the section first.
should no reading blk prod to collector(center pin) and red prod iether way?
Yes at x 1 ohm. If you are not sure you can remove it and retest it again.
i check primary of flyback x’former, 8bars lit!
and when i check HOT onboard of crt tv, it has reading, but when i check HOT offboard, its good. can you give me a little advice for this jestine? thanks and god bless…
Try pull out the yoke coils cable and remove the flyback and see if the HOT still have reading or not when test on board. Sometimes a shorted secondary winding to primary winding in flyback could cause such problem.
This is a power regulator, it has 3 pins, but the collector pin is cut . but interestingly, when I unsoldered it, I found that one of the pins is only soldered and not connected to any part, so I think it is used as a diode.
I have not seen my fault yet, still trying to find it. The set comes on for about 2 seconds and goes to standby.
Cpu first have to receive 5 volts supply and the crystal must have sine waveform. When you press the remote control, the cpu either send a signal to trigger a relay so that thr AC can be supply to the Main power supply and start the TV or it can send a signal through optoisolator to trigger the Main power supply to output full power. If the CPU have problem or the signal did not reach the optosisolator or the relay circuit then the LED will become standby.
Reading your reports/newsletters and the interviews granted by both Steve French and Don Farlow,
to me is like having a sweet dream and I don’t want to be waked up for now.
Am begining to imaging the amount of efforts and resources that were involved in these great works,
I dont know why I or anyone for that matter,that is involve in electronic repairs should miss any of such materials,be it in the past,present or future.
I thank God for your life.
AFOLABI John Adebayo.
: I am about to start into the repair of a power supply. I was wondering, since electronic components are so fragile are you suppose to use a regular electric wire cutter or is there a special one so as not to damage anything. I don’t want to start on the wrong foot. Alan
I usually use a good quality small wire cutter as a cheap one would not last long.
Just wanted you to know how much I appreciated your personal reply to my comments…
I have been sorting out some of my resistors, and I have been constantly refering back to your calculator for the values…. I am getting so I mentally make my calculation, then go to your page to verify my answer.
I have found most of the items to start working on my little police siren, I am just waiting for another order of those transistors to arrive.
Thanks again for your personal touch..
I trying to fix a 17 Aoc monitor you cannot adjust the vertical size of the monitor I already check the sorounding parts of the vertical defection IC everythings seem to be good I am supecting the IC the original parts is STV9302A I have look to the junk monitor trying to salvage some parts I found out there are two similar IC but the voltage rating is a little bit lower I have two TDA 8172 and TDA 9302H I was wondering if it possible to replace the original with the two that I have found in the junk monitor. Again thank you for your support and time I hope I am not disturbing you.
For ICs, sometimes although have similar spec it won’t run when on load. I have not try that out. Since you got the TDA8172 then put it in and make sure it will not run hot. If it is hot then it can’t be used.
May be you remember me, but no mater, I asked you a question 3 years ago hhhhh,
so I need your advice about an IBM flat monitor (lenovo), the screen power on correctly but the moment I connected it to the PC it gives me a flash screen and went black, i tested my PC with the same kind of monitor (IBM lenovo also) it’s ok, if you have any idea or if you have a schema for this kind of monitor.
thanks and have a nice day.
HI O Brik,
It could be bad e-caps problem or one of the backlight have problem. You need to open up the monitor and test the output voltages from the SMPS and if the voltages measured good then suspect a bad backlight.
I am still trying to fix the Samsung lcd, I found out that I am getting 13 volt out of the power board,there is 10 wires coming off the power board going to the control board board. Soon as I plug the cable into the control board the 13 volts disappears.for some reason the power does not get to the control board .Is there something blocking the power
It is either the 13 volt line itself have problem (can’t sustain the demand of load-it can be a bad filter cap) or the control board have something shorted that you need to check it out.
in a muliple regulated power supply if i increase the value of the capacitor from 100uf to 150uf what will happen to the out put voltages is there any dammage to the components in the circuit?
There will be no problem to the power supply.
sir, what’s the nice brand for smd rework station and how much?
Any brand but not the too cheap one. Get a brand that have a moderate price so that it will last long.
Respected Jestine Sir,
Please provide me Pin and Voltage details of IC TEA1504 Supply regulater. Please sir.
Thanks and Regards
Try check this link:
I unplugged it all and then reattached it but now when it press the power button the monitor will only show a picture for about 2 seconds and then goes blank. The green power light stays on the whole time and if I turn it on and off it will show the screen again for 2 seconds and then go blank.
It could be the problem of bad filter cap (e-caps) at the smps that you need to use ESR meter to check it or one of the backlight already have problem.
Dear and respected JESTINE.
Sir after a gape of few days i m contecting to you for your expert openion.
a TV set LG model no CF-21d30R came to me in dead condition. on replacement of STR s-5707 set was ok but after 2 weeks TV set again brought to me with complaint that after few minuts TV goes on stand by position.
In this regard your expertitions are required at periority.
I guess you may need to check all the components in the primary side before replacing the power IC. If you do not have ESR meter then just directly replace all the e-caps in the power supply section.