Electronics Repair Questions/Answers and Testimonials- Part 84

By on August 2, 2011



Dear Jestine Yong, 

Thank you very much for your help regarding the Dell E198PF 19" LCD monitor, what I do is replaced the buldged e-cap 1000microFarad and resoldered all the dry joints of transformers.  

I have another the same model monitor, I also replaced/resoldered the said parts. Now, both of the monitors are now working. 

Thanks again,

Dexter

===================================

HI Jestine,

You are amazing thanks for your effort and dedication, your teaching is so perfect .Since i got the books i do not sleep.

I will come back for the rest. Again i am planning also to budget for all the necessary tools from you

Thanks again,

Samuel

============================

Gud evening,Mr.Jestine Yong,I have downloaded your ebooks LCD MONITOR REPAIR and HOW TO KNOW THE VALUE OF BURNT RESISTOR together with bonus books.I’m glad I had the fantastic books wherein I can get the scientific and proven approach in electronics repair. In the next few weeks I will buy your other great books. 

Thank you,

Jimmy V

=============================

Hi Jestine,
Thanks for the books they are more valuable than i thought. They are a mine of wealth to me.
Evaristo M.

==============================

Thanks for the response to my email Jestine and thanks for the advice.
Since I have so much time invested in troubleshooting my LCD TV, I may have
to try swapping the T-Con board before I give it up as a bad screen.  I’ll
let you know my results.

I’m impressed with the accuracy of your information and the helpfull
trouble shooting technics displayed in your manual along with the great
pictures.  For a young man you are a cut above and I really appreciate your
assistance.  I’m a 69 year old retired Electronic Technician and thank you
for your help.

Philip M

==============================

HI Herminio,

How are you?  It’s been a while since our last communication.

I’m fine thank you.

By the way, i have received all the newsletters that you have sent me. Thank you.

I have encountered error w/ my BENQ SD3731 again and below are the problems

that i have noticed

1.The display is completely messed up in the color department.
2. The settings menus are also all wrong in colors.
3. Switching to an input with  signal gives also also has the same problem.
4. The colors of video are all messed up as seen in the picture
5. Color settings were reset to default, and any other mode doesn’t make it better.. just different.

I have narrowed down the possible problem with the LCD controller PCB but still it did’nt

work. Really need your expertise here. Appreciate your help as usual. Thanks.

This problem is either the mainboard or the LCD panel have problem. Since you said you have narrow down the problem to the lcd controller board then that’s mean most probably the lcd controller ic is at fault. Before that you need to make sure that all the output voltages are good and stable. The problem is it is difficult to get lcd controller ic. Usually if i come across such problem i will buy over the unit from customer since i could not get the parts and atleast i can salvage some of the parts for future use like the power/inverter board, mainboard and even the backlight.

Jestine

===============================

Hi Jestine,

 

I checked manual again and found out some details. Please see the attached,Is these zener voltages are correct or not?    

I like to learn Electronics and always log on your web site. I can not do this full time with my job. But I do some repairs when I am free.

Thanks,

 

 

Hi Pradeep,

Yes this is a zener diode and it should be 22 volt because if the VCC supply voltage 14.3 volt increase more than 22 volt the zener diode will conduct and this will shutdown the ic. In other words the zener diode is use for protection purposes.

Jestine

==============================

HI Lito,

thank you sir for the july updates.

You are welcome!

i have a question sir, since i am also repairing desktop computers and with regards to atx power supply, do we have any codes or software or tricks on how to directly know if the real culprit is the power supply?

..what i mean is sometimes the monitor in blinking, so  i pressume videocard, signal cable and powwer supply. what i did is to replace video card and nothing is happen, then next is i replace power supply the pc back to life, but what if i don’t have a back up pwr supply and i will advice my customer we need to buy new one if things get to worst that after installing the ps nothings happen?..so i did the wrong isolation?..i need to tell the customer to buy video card then let say the pc back to normal..so the customer double his expense..any idea sir? thanks.

Try power on the atx by referring to this link:

http://www.jestineyong.com/?p=267

another thing sir..do you have idea where suppliers of desktop, peripherals and laptop computers on right prices?

Sorry no info on this.

i have also my customer bring in Yamaha Amplifier with no power, anybody from our erg group taking out amplifiers. i check the main but only the pwer cable that has 220v..and that line is going to linear xformer…the connector on the source of xformer has no voltage, please explain how this circuit goes.

Sorry i do not have this circuit but for any linear power supply, the transformer needs ac voltage and produce lower secondary ac voltage. So in your case, does the transformer is getting the right ac voltage. if no ac voltage then you may need to trace backward to see at where the ac had gone missing. If there is ac voltage to transformer but no ac voltage out then the transformer have problem.

Jestine

==========================

 

Regarding this months repair on the “No signal” monitor.  When you checked these SMD devices did you use a standard DVM and did they show an accurate short and open while in-circuit?  Did any of the other devices that checked OK require removal to make sure that they were good?  Consider how difficult it is to remove these things knowing how they check in-circuit is important to me.

 

Thank you

Hi R,

For your information the article was written by Mr Kent but anyway checking SMD devices generally has to be off board. If you check smd resistor on board and you do not get reading then it is indeed has open circuit. If you get lower value then most probably it is parallel with other component.  If you get high ohm then most probably the resistor has turned into high ohm. In order to remove smd component you need a smd rework station.

Jestine

============================

 HI Ross,

I have attached a couple of photos of the power supply I am trying to repair.  IMG_2996 shows the PCB — I have removed a number of heat sinks from around some of the FETs and rectifier to aid clarity.  IMG_2997 shows the FET I am concerned about. 

There are four components on the 12V side — the K2611 FET, which is the one getting hot and could have something to do with my output issue, two 20N60S5 MOS Power Transistors and a diode R1560P2.

I have the same symptoms when I connect up to the original load (a Cisco network switch) as I do when I connect up a 5 Ohm test load.  When the PSU does eventually give 12V (after about 1 minute — should be instant!) it draws around 2.5A when connected to Cisco switch.  The 5 Ohm test load will draw 2.4A.

Once again, many thanks for your help so far, and if you could offer any further advice on what I could check, it would be most welcome. 

Thanks for the photos. Since the FET is getting hot and drawing up amps, i suggest that you check all the components connected to it. Before that try power up the power supply and wait till a minutes, remove the power cord, quickly discharge the big filter capacitor and use your hand to touch on all the components. Besides the hot FET and if you could detect another hot component that means that particular component is the cause of the problem.

Another reason why the FET is hot was because the the gate signal may have problem. Try trace from the FET gate pin and see if there is any bad components.

Jestine

=================================         

Dear Jestine

I have found two ecaps on one board that have these values – 35V   680uF .

When tested with the blue ESR meter give 0.00 on the meter which, I guess, suggests that they are shorted. I have ordered some replacements which was very cheap and we will see if this will improve the picture.

I will keep you informed as to the progress.

Regards

Jeff

HI Jeff,

You can confirm if the cap is shorted or not by using your analog meter set to x 1 or x 100ohm. Sometimes the blue esr meter probes cable too long also could give such reading.

Jestine

=================================

Hi Jestine.

Remember I talked to you about an lcd pannel 22.8 from a Dell to be exact with lines in screen. Well I had another 22.8 that had back lights burnt out and I knew back lights in bad screen with lines in it were good. So I just prayed as I started to pull both screens apart and swap their back lights and now I have accomplished my first back light replacement on black & silver 22.8 Dell monitor and everything went together quite well on the screen with burnt out back lights. Now I have a good working 22.8 Dell LCD after rebuilding inverter board also. It’s very tricky lining up all the plastics inside the display but it worked and I am very happy about it. This is my first accomplishment in doing that.

Gary

====================================

HI Jay, 

I was repairing a Sony 29" TV at a customer site, cannot switch on.  Found the HOT and some components failure, changed the HOT and the components of the same value, now the TV turns on and the picture and sound are coming  okay, except that the picture color is very dim and scanning lines can be seen on the screen.  I set the brightness, contrast, color, etc of the TV and after a few minutes the picture colors dims by itself.


Make sure the heater supply to the tube is good. If you could see a bright orange light then you will roughly know that the supply is enough otherwise check the heater circuit. Next it could be the problem of weak picture. Before that make sure all the voltages at the CRT board pins like the G2, R, G, B, G1 (if have) are good.

Jestine

=====================================

Dear jestine,

(5 volt line)voltage reach to the main board but i don’t know reach or
not to lcd.How can i test lcd voltage?How many voltage will reach to
lcd?Can i test lcd voltage without connecting lcd?

Thank a lot for your reply.I will looking forwards your reply.

Best Regards,
Linn

HI Linn,

Usually 1.8v, 2.5 v or 3.3 v depending on the model. Some lcd panel have a small smd fuse and if it blow then there willbe white display. You can test the lcd controller ic voltage in the lcd panel using your dc voltmeter . Just carefully place the probe in one of the pins and it should show the voltage (1`.8, 2.5 or 3.3v).

Jestine

=====================================

dear justin

I happened to visit you website,and wonder you could help me:
I have a SONY TV(kv2092) the problem is with the power supply section
when powered ON the fuse blows along with the chopper FET C3679,( the costliest part and hard- to-get
in my country).Bad /cold soldering was suspected and all the critical points was resolidered (using good quality lead)
suspected leaky capacitors and power diode/zenners replaced, there is nothing short in the HORIZONTAL&VERTICAL sections,
if this set powered with an external 115V power supply salvaged for another TV the sets works fine….my efforts to assemble a
115v power pack for this set ran into rough weather, I seek your FREE expertise and if you can help me to troubleshoot this  power-supply
I shall be glad. It is not understood why SONY has provided short circuit and overload protection in their power supply design,
pls be kind enough to send me a reply, also help me design a 115V B+ (14v,7v) power pack for this set which will be sincerly appriciated

yours truly

Abraham

Hi Abraham,

FET part number should start with "K" and not "C". Perhaps the FET could be K3679. In your case, you need to check all the components in it which include the transformer primary winding and also all the secondary diodes. If all check to be good then you may need to replace the power IC and retest. Generally when the power FET shorted the power IC will give way too.

As for the power supply design sorry i do not have the diagram.

Jestine
http://www.JestineYong.com

==================================

i have my customer crt monitor who is 1/2 ic clear picture and 1/2 is dark at the bottom please assist me sir.

lito

HI Lito,

Make sure the 2 supply voltages are good to the vertical ic. If all check to be good then direct replace the vertical ic and retest.

Jestine

====================================

I have a dell e151fpb flate screen that needs a 2n7000 fet replaced. where can I buy the right. i tried googling it and it seems some are 200ma and some are 500ma

I went to radio shack and they have the n channel

HI David,

 Try this link:

http://www.utsource.net/2n7000.html

Jestine

===================================

Hi Jestine,

        I’m sorry for delay to reply your mail,because I could not get internet before.I like to study any new technology base on mechanical and electronic.Now,my professional job is mechanic,also,I like to repair electronic like a professional job.

        When I was in childhood,want to know about why lighting the bulb when we switch on.After that I want to know how come out the sound from radio,so,I asked to my parent,they just answered that is converted from radio frequency in air to sound.I asked how to convert?They was answered by electronics and nothing more.so,I want to know what is in inside.One day,no bodies at home,I was opened and checked inside,what are these?Never see before.When I was about ten years,I saved money and bought "how to work radio and repair book".And then,I read that nothing understand to me.But I got once thing need to study how work electronics component.During summer school holiday,I went to electronics repair shop of friend of my uncle.He told about name of the parts and troubleshooting,I asked about how is working each part,he said that he’ll teach me later.That time I not like to study about troubleshooting.So,I did not go to him,after few weeks.

         When I was in end of secondary school,I was found a book of basic electronic course.I’ve satisfied after read that book.When I was in high school,I was start studied about applied electronic course by reading the books and building the some electronic projects like as transistor switch,scr switch,triac switch,preamp.Almost of projects were successed.But so many parts were burnt cause by I tested by changed bias volt.I remembered when I built first transistors amplifier not worked,It was troubleshooting about 3 days,after 3days some components were useless because their legs were broken mostly on transistors.So I bought some parts again and rebuilt.After that,I started to fix some things from my home.Some things were easy to fix and some things were very difficult for me even on minor case.And then I repaired free of charge every not worked things from neighbour.

        After finished high school,started to prepare for marine engineering,that time,studied about mechanical theories and principles.By the way,I compared between electronic and mechanical,mechanical is easy to study than electronic if understood theories and priciples,that is my opinion.Because all machinery parts are we can observe physically.When I’ve been in India,I bought many books of mechanical,electrical and electronic,and studied on at sea.I prefer to read theory and caculation than troubleshooting.Then,I bought some electronic components and tested some circuits when I stay onboard.

        When I vacation at home,some of my friends came and asked to me about troubles of some electronic,they are repair electronic as proffessional job.Mostly,they can solved according by my answers.So,they thought I can repair more than them,but one day,one of them brought one of TV circuit board,he said that no +B volt,if got +B just enough.That time,I got start problem,because cann’t fix without schematic diagram.I asked to him about diagram,he said that they never use these.He said if possible to repair time is not problem.So,I’ve found and bought schem: from book store.And I was fixed it.But I spent about 8 days.That time,I understood theory and troubleshooting are difference.But i’ve confidence about repair the PA amp.Because they said that some pa amp repaired by others,burnt again a few minutes use and could work like as original after repaired by me.Because I changed not only burnt components but also checked other stages. 

         When I saw your burnt resistor value book in 2009,I was very interested and tried to buy this book but I’ve not paybal card.So,I asked to all of my friends,who use credit card?Nobody use.So,when I arrived in usa,I requested to seamen mission to buy this book,then I read immediately.I sastisfied after read,because i never think so that we can find by this way.I though so we’ve to caculate by electronic theory before read this book.So I believed you,then I bought smps repair book and lcd repair book continously,after read the smps repair book,I understood clearly and I’ve believe myself,I was been repaired smps difficultly before.Now,I can be repair any smps easily.I’ve read several books of smps,these are not so much supported to repair.

         If I srart repair electronic as a proffessional job,I need much your help and I’ve to learn about troubleshooting and repair by your books.Tell me,please,do you have any idea for improve to me.

Mr S

HI S,

Nice to know about your background in electronics and it was so interesting! Thanks for the support on  my ebooks. If you have any questions on electronics repair just do not hesitate to email me. By the way, to improve your repair knowledge one need to read lots of book on electronics, visit repair forum and most importantly repair as many electronics equipment as possible. Practical works really count!

Have a good day!

Jestine

=================================

Hi Jestine,

 
Jestine i would like your advice on a matter that i want to ask for some time. While doing voltage test on crt monitors and televisions is it safe (ok) to remove the board completely from the case and the connectors from the tube including the high voltage wire and do the tests as long as i take care to stay clear of the big red wire (HV) ?

 Thank you.

HI Eric,

If possible do not remove it because in certain circuit some components will blow if there is no load and to some, the circuit will shutdown. The best is to have all the connectors connected.

jestine

===============================

Hi Lito,

i did it sir, i made back to life the vertical problem, it just a cold solder on the IC…thank you so much. I have the voltages but i dont know why after i have solder the ic terminal where the voltages are..back to life  AOC 15" crt monitor.

Ok congratulation! You have soldered the right pins thus the picture came back.

 

sir beyond the SMPS of your e-book where do I can find problems/solutions of CRT monitor as my guide to repair?….there’s a lot of crt here they declare beyond repair. please help me.

Try this link:

http://www.repairfaq.org/sam/monfaq.htm

Jestine

============================

HI Richard,

i will buy your books as soon as funds are available.they seem to be prety good books.

Thanks for the support!

i have a panasonic tv and this is what it does.at times it shows normal picture.but then

most of the times it shows half pictures the top cliped and has many small horizontal lines i.e the half top.then at times the screen goes

black with only a sharp line in the midle of the screen .please assist me this is irritating i have tried to soder on components on the board thinking maybe it could be due to dry joints but to no avail.help my family wants to watch. mambwe

Check the vertical ic and make sure the supply voltages are good and no dry joints in this vertical ic and the corresponding area.

Jestine
http://www.JestineYong.com

===========================

HI Roger,

You need to check if there is supply to the video pre-amp ic and if possible try direct replace the pre-amp ic and retest. I don’t suspect the vertical ic because you already get full screen.

Jestine

sir good day to you,,,,pls advise me sir,,,,,i have check 14inch crt acer monitor,,for the first time,,,,the problem is,  one bright horizontal line at the center of the screen,,,i open the cover,,and i head straight to vertical section,,,i scan dry joints,,,i resolder the vertical ic,, and re test,,,the one bright horizontal is gone,,but only blue display appear on the screen,,,i re solder also dry joints at the crt neck board,,,no lack,,,,so i perform voltage checking at the 3 cathods,,,,it reads 53v,,56,,,57,,,i noticed the supply voltage is not level,,,all secodary volts is ok,at the smpt,,,the 75v supply at crt neck board is slighly low to 73v,,,i scan the e-caps at the crt neckboard,,,rated 1uf/100v,,2 were reads high,,,so i replace,an test the voltage at the3 cathods,,,all rated 57v now,,,but the sreen is blue display again,,,i check the esr of 75v rails e-cap,,its high reading 25 ohms,,so i need to replace also,,,,maybe my analysis,,,it is possible the vertical ic itself is gone sir?i try to chek the pins of vertical ic voltages,,,many pins reads 5.36 something volts,,,one pin read 41.5v,,maybe some pin of vertical have short,,am i right sir?pls..advise me sir,,,,thanks,,,,by the way i pull out the whole board to acces my repair,,,because its very hard to chek the components inside the board,,,,,,thanks ,,roger

==============================

Hi,
Sir, how are you.

  1.  I have Sony KV-TF21M90 TV with A51LPT70X Picture Tube.The green and Red Gun    Colors are very good but the Blue Gun Color is very low.how to repair it.&
  2. How to repair TV Heater-Cathode Blue gun Shorts. thanks

 

HI Masuri,

I suggest that you check on this link and the related articles:

http://www.repairfaq.org/samnew/tvfaq/tvbrightcrt.htm

Jestine

==================================

hello jestine, saya ada 2 atx pwr supply dan saya mahu modified untuk di gunakan pada radio amatur saya.but i have 1 problem here.ampere dari atx pwr supply tak cukup untuk transmit.bagaimana cara hendak menaikkan ampere power supply tersebut.saya berharap agar sir dapat membantu saya to settle this problem. regards mic

HI Michael,

Sukar untuk naikkan ampere output krn biasanya ampere ditentukan oleh switch more transformer dan transformer ini tidak boleh ditukar.

Jestine

==================================

HI Abraham, 

thanks for the mail, with the fuse blown and the switching power transistor burnt/shorted how to test the voltages?

What i meant was you have replaced the components and it did not work, in order to do the troubleshooting one can power on the unit and compare the readings/measurement base on the schematic and hopefully to locate some bad components.

I am afraid repowering the unit again may  further damage the other components (which are hard to get in my country,)

I seek your expertise in this regard ,my faithful friend is my old  Analog Multimeter, the transformer was removed from the board

and the ohmic test was conducted on the windings with the meter that is all as I don’t have any other tools to test it more than that…..kindly guide me what other test to be done on a switching transformer, I value your expertise with immense regard and  appriciate the time and patience to reply to my quiry

If you have check all the components (i mean really have tested all the components) and it still did not work then the transformer is the suspect. Transformer can only be tested by using a
Blue Ring Tester because a shorted transformer winding, analog meter will not be able to check it. Analog meter is to check for open circuit only in the winding.

Jestine

================================

HI Abraham, 

Thanks for the mail, so the transformer is the culprit, So I have to replace the transformer(T603)

If you have check all the components then the only component left are the transformers. But you really have to make sure that you have truly check all the components.

can a short in the driver transformer (T602) damage the power transistor?

There is a possibility. In electronics circuit if a components is located in the same area then there is chances the particular components can cause other components (in the same circuit) to go bad.

 kindly enlighten me on this ….SONY has discontinued this model years back and  getting the original transformer is tough,

Is it advisable to rewind the transformer?

It will be tough to rewind such a small transformer. Many rewinder usually only rewind bigger transformer.

is there any way to protect the power transistor,I have tried additional fuses in the B+ circuit but it did not work as the transistors burn to protect the fuse, I seek your valuable expertise in this regard, I thank you again for your prompt reply

The only way to protect the power transistor is to replace the main fuse with a 100 watt bulb. If the bulb very bright you know that the circuit still have problem. If the bulb went off then you can place back the main fuse and power on.

Jestine

=================================

HI Drax,

Am just enquiring about the schottky diode if  how many types of schoottky diode.

There are many few types (physical package) of schottky diode and each type is depends on the part number.

2. Do you have any example in using oscilloscope wave form to identify the faults in the circuit or even the werbsite so that we can easilly access for reference.

This is a big subject- Sorry i do not have such example. I suggest that you search from amazon.com for using scope on how to troubleshoot electronic circuits.

3.About the data sheet for electronics components like IC and so we can compare the Schooty  diode and a normal diode.


The best is to replace a schottky diode with another schottky diode. Please do not replace with a normal diode as it can go shorted easily.

4.Do you have any online for electronic forum in case for asking some question regarding repair and trouble shooting.


There are many. Just type in Google " electronics repair forum" and you can see a list of them.

Jestine
http://www.JestineYong.com

=============================

I have NEC lcd monitor which goes blank in seconds and when you switch it on again it comes up AND GOES BLANK AGAIN. I have checked the power section and found some swollen capacitors(470uf, 25v) and one 220uf 25v capacitor which I changed with the same spec. but on trying it the problem repeats with the exception that the monitor no longer goes hot. Kindly assist me

thanks,

HI Nelson,

Make sure the inverter ic is getting supply voltage and no dry joints in the high voltage transformer. If all check to be good then suspect one of the backlight have problem.

Jestine

============================

I just bought a second hand oscilloscope airon 2channel but dont know how to use it any idea u can advise me.

Hi Jamaludin,

Using scope is a big subject and there are many books at amazon.com that can fully explain how to use a scope. However in electronics troubleshooting, we just use either DC or the AC setting depending on what type of signal you are testing. If you want to test on DC then set to DC and place your scope and look at the waveform and the setting of the volt per division. A good dc voltage should be a straight line. For checking signal then you need to set to AC. Place your probe at the test point and look at the waveform by adjusting the volt and time per division. You must know what type of waveform you should expect before placing the probe. If you expect a square wave and get no waveform then you know that particular point/circuit have problem.

Jestine

 

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4 Comments

  1. Chandrei

    August 2, 2011 at 9:53 pm

    Hello Jestine,

    I was repairing a dead TV set and found out that the HOT transistor was shorted. I replaced it and also replace the snubber capacitor. When i turned it ON it just worked for about 5 minutes then the HOT get shorted again. I suspected the FBT, i removed it from the board and brought it to the nearest shop for testing but the result was the FBT is good. So I soldered it back to the board. Tried replacing all filter capacitors sorrounding the HOT transistor but when i turned ON the set, again the HOT get shorted after a couple of minutes.

    Can you help me in fixing this trouble? what are the other causes of this failure?

    thanks in advance!

    Chandrei

    Likes(0)Dislikes(0)
  2. admin

    August 3, 2011 at 6:41 am

    HI Chandrei,

    Please visit this link:

    http://www.jestineyong.com/?p=403

    Jestine

    Likes(0)Dislikes(0)
  3. rahim

    July 5, 2012 at 2:17 pm

    hi
    i use ATX Power Supply for my design power unit
    i must cancel ATX powers overload protection please hellp me
    i jast want know how its work
    thank you and excuse me for my mistake full English
     

    Likes(0)Dislikes(0)
    • Jestine Yong

      July 6, 2012 at 7:47 am

      HI Rahim,

      It is not easy to cancel such protection if there is no schematic. Even with schematic one has to do some test or research to cancal and this will take time.

      Jestine

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