Friday, November 5, 2010

Solving power supply problems (s.m.p.s)

Most problems with equipment using switch mode power supply (s.m.p.s) like television and monitor are power related, this is because power supplies runs under considerable stress due to high voltages and current involved around these circuits.


In order to understand how to solve s.m.p.s problem I am going to show you how to analyze common failure mode in CRT television, you can use this principle in repairing CRT monitor too.


Case One: CRT Television Dead

Here dead I mean the set does not show any sign of life, power ON LED is not lighted and nothing happens even after power is switched on.

First confirm the television power cable is not broken inside, you can check this by measuring the voltage across the AC power input connector on the circuit board.




If the voltage is reaching the circuit board, then look for the fuse and see if it is blown, if the fuse is okay check also the surge limiter is open or not.

If these two components are okay then most likely there is no short on the primary side of the power supply.

Note:Short in the primary side of the power supply usually cause the surge limiter or the fuse to blow.

From now on we shall be using the main capacitor negative as the Ground for all the measurements of the voltages on the primary side of the power supply.

I have modified my meter ground probe with a crocodile clip so that I can attach it to the ground point of the equipment I am repairing and therefore I use only one hand to probe the circuit.

This is safety precaution because as you know for there to have a potential difference there must be a connection between the live and the ground.

So if you are using your two hands and incidentally touch the live and the ground then the current will flow through your body and this can be fatal. But if you are using one hand it is not possible.




One thing I have learn in electronics is that if you master doing your troubleshooting using voltage tests you will have an added advantage because in electronics it is not always the component that fail but it could be just a crack on the circuit board that is preventing the voltage to flow or even dry joints and therefore if you concentrate on looking for the bad component you are going to waste a lot of time and end up not repairing the set.

Therefore I encourage you to narrow down to the faulty circuit (area) by using voltage testing only. This one is very fast and valuable method I have come to learn.

Now set your meter to DC range of 1000VDC and use the main capacitor as your ground.

First check the voltage across this main capacitor and if you get around 300 vdc on 220vac outlet or 150 vdc on 110 vac outlet then it is assumed the supply is okay up to the main capacitor.

If there is no voltage at the main capacitor then check backward looking for open component or circuit board cracked or dry joint on the power path.




Be sure this main DC(300vdc or 150vdc) is reaching the power regulator ic collector/drain pin, Now still using the same ground move the positive probe and measure the vcc-IN pin of the power regulator ic.



Depending on the regulator used you can check the correct vcc-IN Supply (start up Voltage) from the data sheet for the ic used from the internet.

These two voltages are very important and if any is missing the supply will appear dead, if the vcc-IN is missing this means there is a open circuit or start up resistor is open.

Follow backward and find what is preventing the start up voltage from reaching the vcc-IN pin.

Another hint: if you see this vcc is less than normal and pulsating there is a possibility that there is a short on that pin, to confirm just lift up that pin and if the voltage increases then it means there is a short on that pin internally and the ic must be replaced.

There is also a filter capacitor for this source usually 100uF/35V, please check the ESR of this capacitor or directly replace it if you don’t have an ESR meter.

There is also a resistor linked to the source pin of this ic called the current sense resistor which sometimes open or change value and this can cause the power supply not to start. Usually it is a very low ohm resistor, less than 2 ohms and around 2 watts so it is a big one.

If up to here you have checked and everything is okay, then you should suspect a short on the secondary side of the s.m.p.s.

First measure for short of any of the secondary diode using analogue meter set to X1, when you measure across any diode on the secondary you should not have two reading and if you get two reading lift up one leg and test again. If you still get two reading then you can conclude that diode is shorted.

Also when using this method and find that the diode has two reading in-circuit and when lifted up you get one reading, it could also mean there is a short on that source (line).

You can follow that source looking for the shorted component; usually the most common components to short are transistors, ics, diodes, capacitors.

Remember when doing voltage testing on the secondary circuit you should be using the COLD GROUND of the set.


The best cold ground to use is the turner ground (out part) or the CRT ground return.




If you find still there is no voltage at the secondary output or the voltage is low, it is the time to substitute for the main B+ Load with a dummy load.

You can make a dummy load by using a 40 watts bulb/250 vac, a bulb holder, crocodile clip and a wire(read and black) and connect them as shown on the picture below.




Now identify the main supply to the fly back called the B+ and disconnect the supply just before the fly back B+ vcc pin. Don’t cut the circuit board to do this just lift up one side of a resistor( high wattage) in series with this B+ voltage or sometime they use a jumper wire just before the B+ vcc pin of the fly back and attach your dummy load between this point and the cold ground.

If the bulb light steadily and you measure between 90 Volts dc to 140 dc depending on the size of the television then you can assume that the s.m.p.s is okay and the problem is on the secondary side.



Full report is available in pdf format, 

 Download for free NOW!!!





By Humphrey Kimathi
Author CRT television repair course





126 comments:

  1. thanks for sharing this information. Waiting for more :)

    ReplyDelete
  2. Keep up the good work.

    ReplyDelete
  3. Hi my two friends without names...thank you for your kind words and you are both most welcomed to humtech electronics 24/7.. kindly leave your name next time you comments...here everybody is somebody and we like addressing one another by their names...pls comply.

    kind regards

    Humphrey

    ReplyDelete
  4. Great work, very useful informations,
    Keep going.

    ReplyDelete
  5. hi nameless...thanks for your encouraging words.. wish you the best.
    Humphrey

    ReplyDelete
  6. good article. thanks for sharing.

    ReplyDelete
  7. Thank you for visiting us & comments mr Nugroho...
    Humphrey

    ReplyDelete
  8. hi i have panasonic tv there is no audio and if i have to turn on the tv it will work but in a second it goes shutdown..will help me for this problem.

    ReplyDelete
  9. let me have a detailed behavior of this TV via my email given elsewhere on this blog.

    Humphrey

    ReplyDelete
  10. hi sir,can i have your email add please so that i will send u details regarding in my panasonic televesion...

    ReplyDelete
  11. thank you to your blog. many information about your electronics made easy is my very best guide in my work as a beginner's in electronics. may be soon , you can teach me how to perform about voltage reading.

    ReplyDelete
  12. Halo Friend, most of my troubleshooting method i use voltage testing and therefore if you have been following me then you are on your way up of becoming a pro in Voltage testing and analysis. watch this space.

    Humphrey.

    ReplyDelete
  13. Nice e-book; one of the bests of TV repairs I got in my hands, no more need to order complex books in library or thru internet.

    Thank you very much for sharing your works.

    Patrick M.
    tahiti-french polynesia
    south pacific

    ReplyDelete
  14. Hi Patrick, Thank you for your encouraging words and buying my ebook..hope you will continue to find it a valuable resource at your work bench.

    kind regards Humphrey

    ReplyDelete
  15. What a nice article on tv repair...it's good to see a tv repairman that wants to share his knowledge with us. Sometimes I start by first checking the HOT (Horizontal Output Transistor) as this often blows and can also blow out the Power Regulator as well.
    Thanks again for your article, I have been doing tv repair for some years but I am still learning and found this article to be really helpful.

    ReplyDelete
  16. Hi Friend, Thank you for your nice comment. Again happy to note that you are keeping yourself updated by continually learning which is synonymous with sharping the tools for fast diagnosis and repair. Kind regards humphrey

    ReplyDelete
  17. hello sir, i have JVC model AV-20NT11
    symptom: power comes on, but after 3-4 secs, it will turn off and standby led continues blinking

    any idea about this?


    resolder cold soldered joint on power supply section and near flyback section done but no luck


    i found out that: before it turns off i measured B+ it has 125 volts, secondary regulator ic BA51w12st input 14 volts (pin2)output of pin1 9volts and pin4 5 volts meaning ok, but after 3 -4 secs it will drop to B+ 85 volts, input of BA51w12st drops to 10 volts, pin 1 =0 volt, pin 4 0 volt

    jungle ic has 9 volts before 3-4 secs after 3-4 secs become 0 v
    system control ic has 4.8-5 volts --

    for BA51W12st is a dual out put reg
    pin 1 out 9v
    pin 2 input 10-25v
    pin 3 grnd
    pin 4 out 4v
    pin5 control from system control IC

    i already replace the following:

    jungle IC,primary reg STRW5753a, hor Transistor D2627, and vertical IC AN5522

    pls help

    doodz

    ReplyDelete
  18. Hi.. use the dummy load described above to isolate if the problem is on the primary or secondary side of the supply and come back to me.
    regards Humphrey.

    ReplyDelete
  19. btw, i didnt found any defective components yet, but i did replaced those components mentioned above but still no luck..

    doodz

    ReplyDelete
  20. thanks for reply sir Humphrey
    as i hung the coils to going to the other section like B+ it reads 125 v and the other supply voltage 14 volts

    and when return the coils to its connection B+ drops to 85v. on the hand, input of secondary regulator drops from 14 to 10 v and no outputs

    ReplyDelete
  21. email me at: humtechelectronics@gmail.com for details of this repair. if possible include pic and let see how it goes.
    Kind regards humphrey

    ReplyDelete
  22. i had repair sharp tv 21inch but the problem theres a sound but no picture can yuo give an idea of this trobol sir humphrey

    ReplyDelete
  23. Hi..is HV present? heater is lighted? screen voltage 300 vdc? is there something on the screen of just blank screen?
    see this link for more info...
    http://humphreykimathi.blogspot.com/2010/12/lg-tv-14-no-picture-audio-ok-blue.html
    kind regards
    Humphrey

    ReplyDelete
  24. Another great, well written, & very practical, "how to" article from a very helpful person.
    Thankyou Humphrey.

    My last TV repair (by professional tech not myself) revealed multiple failed solder joints, the repair chap resoldered about 230 odd joints, not all were faulty but he suspected they might soon become faulty.
    The TV was a CRT 34" Mitsubishi about 15 years old.
    My question is why do good soldered joints in a reputable brand TV not known for problems develope & where do you look fore these "most likely candidates". I ask because I gather its a a common problem.
    Can you also please explain what a "cold ground" is. I have never before heard this term.
    Again thanks for a great article & your obviously willing help top readers.

    Peter O

    ReplyDelete
  25. You are most welcome Peter...Usually electronics equipment age like human being...so we can't really blame the manufacture really..In your case 15 years in case of your TV was job well done by Mitsubishi company...most of the new Tvs start this problem in less than 3 years of continuous use.

    This is usually good news to technicians but sad news to the owner.

    Usually the problem of dry joints is very common around big component like the transformers like smps transformer, flyback transformers and surrounding components, also capacitor pins and Big transistor pins and on cathode pins of crt neck board

    "Cold Ground" is a ground which is isolated from the live side, usually refers to all the ground on the secondary side of the switch mode power supply(smps)

    Kind regards

    Humphrey

    ReplyDelete
  26. Hi Humphrey,

    I need help on my dead TCL-2111 TV. Here are my observations:

    - power LED blinks
    - CRT no power
    - B+ voltage measures only about 50V and pulsating.
    - No High Voltage

    I have already done the following:

    - replaced the Horizontal output transistor
    - replaced the BUZ91A Power MOSFET switching transistor
    - replaced the TDA16846 SMPS IC.
    - tested the flyback OK
    - tested the horizontal driver transistor OK

    I need your advice on what to do next. Help

    Glenn

    ReplyDelete
  27. Hi Glen, i suggest you use the dummy load outlined on this article. if the bulb is stable and you are able to measure around 90+Volts then you can conclude that the power supply is ok and you should concentrate on the secondary side of the supply.

    Regards Humphrey

    ReplyDelete
  28. Hi Humphrey,

    Here is an update on my troubleshooting:

    - I replaced a leaky filter capacitor (220uF/160V) in parallel with the B+ supply
    - Now the B+ is normal (112V) BUT....

    -The CRT still has no power
    -The secondary/auxiliary windings of the flyback has ZERO volts.

    I suspect an open or shorted auxiliary winding on the flyback...

    Am I right? Please advice before I buy a new flyback...Thanks for the quick reply

    Glenn

    ReplyDelete
  29. Hi Glenn, Now that the B+ is steady, check if the horizontal drive circuit is working ok,any voltage at the collector of the drive transistor and at the base of the drive transistor?

    For the flyback to work it will require the two circuits mensioned above to be working otherwise it will not work.

    regards Humphrey

    ReplyDelete
  30. There is a voltage 112V at the collector of the drive transistor (the same as the B+ I suppose). But there is no voltage at its base.

    The base is also directly connected to a horizontal drive IC (large one with 56 pins) so I suppose the horizontal drive signal comes from this IC. How do I confirm if the IC is faulty? By the way the IC is TB1238N.

    Thanks

    Glenn

    ReplyDelete
  31. Hi Glenn, lift up the base leg of the drive transistor and see if the voltage at the base appear. usually there is a resistor in series with the base of the driver transistor..test the voltage on both sides of this resistor with the base of the driver transistor dis-connected from the circuit and see if you get any reading. also i suggest you change the driver transistor and filter capacitors for this circuit directly not forgetting to check for dry joints.

    Regards Humphrey

    ReplyDelete
  32. Hi Humphrey,

    here is an update:

    I replaced a leaky capacitor on the horizontal drive IC. Then to my surprise, here are my new observations:

    - after I press the power on switch, it takes about 2-minutes before the TV powers up.
    - the picture is compressed from top to bottom or is about only 3 inches in height so I suspect a vertical deflection problem
    - no sound can be heard
    - no video can be seen except for the MENU selection display
    - i cannot control the TV/Video selection

    It seems there is a problem with the EEPROM controller IC or the vertical IC or its associated components.

    Any advice? By the way, thanks for the previous advice. I almost bought a new flyback.

    Glenn

    ReplyDelete
  33. Hi Glenn, thank you for the update, i suspect a lot of leaky capacitor in this set, if you have an esr meter use it to the maximum...so far i don't suspect any ic. also be sure to re-solder all dry joints in this set. all the best

    Regards Humphrey

    ReplyDelete
  34. Hi Humphrey,

    I dont have an ESR meter. I only use my multimeter to test capacitors. Would this be enough?

    Glenn

    ReplyDelete
  35. Hi Humphrey,

    I also noticed that after about 10-minutes, the TV would suddenly power off by itself.

    Could you show me a tutorial on how to spot dry joints?

    Glenn

    ReplyDelete
  36. Hi Glenn, To accurately test the health of a capacitor the best test equipment is the esr meter. if you don't have one by now you are missing something great..to make one follow the link below for more info.

    http://humphreykimathi.blogspot.com/2011/06/make-your-own-esr-meter.html
    regards Humphrey

    ReplyDelete
  37. Hi Glenn, Dry joints basically refers lose connection on the PCB, the best test equipment is your eyes...just check from the underside of the board and whatever joint you are not happy with should be re-soldered again. you can also use magnifying glass if need be.

    regards Humphrey

    ReplyDelete
  38. Thx vry much. The spirit of Yahweh led me to this web, after sleepless nites of trying to find a faulty on a westpoint tv. Tomorrow i will be printing out these notes, for there are straight forward to understand and good illustration. My God reward you.

    ReplyDelete
  39. Hi Kesa,
    Thanks for your positive feedback, May God bless the work of your hands too.

    Regards Humphrey

    ReplyDelete
  40. I need more example with pics on cold and hot area

    ReplyDelete
    Replies
    1. For more info on this and much more consider investing on this book on CRT Television repair course.

      http://www.humphreykimathi.com/crt.html

      Regard Humphrey

      Delete
  41. earlier i repaired a JVC tv it was white screen then blurred then after 30 mins people are visible and has normal color, not blurred anymore but has blue lines on the right side and fine black horizontal lines...

    i changed crt socket, bec. its corroded, screen not anymore white and or blurred but the last problems are the blue and black lines, what do you think should I do next?

    ReplyDelete
    Replies
    1. Hi Teleg, This Tv sounds like it has a lot of dry joints...please consider re-soldering all dry joints on that set and see if things will improve. if that doesn't make things to improve kindly send my the screen shot of that TV.

      regards Humphrey

      Delete
  42. Hello sir, i have a problem with LG CRT TV. My problem is that when i pressed power switch, red LED at the front light about 2 seconds, but tv shows no sign of life. At a good LG TV, red LED at the front ligh during the TV set is on. Please tell me what to do?

    ReplyDelete
    Replies
    1. I suspect a short on the secondary side(overload),what is the situation when you substitute the B+ with the dummy load as described on this lesson?

      Regards Humphrey

      Delete
  43. Hi Humphrey,

    My 21" TV is cycling on and off (every seconds interval), what is the possible fault of this?
    At first, when I power on (switch on) the unit, it seems ok, but after a couple of minutes, it turns on and off.
    Please advice.thanks

    Regards,
    James from Philippines

    ReplyDelete
  44. Hi James, this could point to a component which is getting overheated. power on the tv with the cover off and wait till the symptoms presents again. power off the set and remove the power cable from the outlet and touch components around the primary and secondary power supply and whatever in getting very hot should be replaced...start with capacitors then ics
    regards Humphrey

    ReplyDelete
  45. hi I have a crt tv lg cp29m30 model there is no power but the lamp indicator is lit. i have change already the main capacitor and the switching ic (str f6456).
    could you please help me and give me some hint on how to fix this problem. also I have change the flyback transformer.
    thank you in advance

    ReplyDelete
    Replies
    1. Hi there, if the power on indicator was on,, this means the primary power supply is working well and therefore there was no need to change the STR F645 and the main capacitor. So you need to concentrate on the high voltage circuit and the RGB circuit…is the HV present? Screen voltage? Heater bulb lighted?
      Regards Humphrey

      Delete
  46. Hi Humphrey,

    I have learned a lot while reading this.
    Thank you very much.

    Regards,
    Chris

    ReplyDelete
    Replies
    1. Hi Chris, Thanks for your feedback..you are most welcome.

      Regards Humphrey

      Delete
  47. I am troubleshooting a power problem with a 1988 35" Mitsubishi CRT. There is sound but no picture. I think the problem is with the rectifier diodes or caps. I have 33.4 volts on the supply side of the standby and main bridges. The standby has -2.5 volts and 73 volts, the main has 0 and 86. All of the large resistors around the main power supply are cold making me think that it is doing nothing. Voltage on the standby IC 3 pin is 0 when it should be 174, Main IC pin 3 is 82.3 sb 166. Does this give you enough information to head me in the right direction?
    Many thanks,
    KA

    ReplyDelete
    Replies
    1. Hi KA.
      The fact that there is sound but no picture is enough evidence that the power supply is working well and therefore you should not waste your time there.

      You should now concentrate on the horizontal output….is high voltage present? Is the heater lighted? Screen voltage present? RGB amplifier supply present?

      Regards Humphrey

      Delete
  48. Hi Humphrey,

    Thanks for your untiring support to everyone who needs your helpful tips and advise.Almost everyday i visit this blog never get tired of reading all problem and solution.Any l have also a problem to share with you mr.humphrey about sharp crt tv cinemaborg that i'm troubleshooting for 3days and yet still looking for the culprit.The problem for this tv power on the primary and secondary and measure the b+ is 150vdc but base on schematic it should only be 115v b+.Notice also a no voltage reading @the primary winding of the Horizontal driver transformer.I try to lift up one leg of the resistor in series to the base of horizontal driver transistor from the jingle ic and measure the collector of the horizontal drive got a 150vdc same as to the b+ of flyback.Resolder the base resistor and hang the horizontal pin drive of the jungle ic voltage still present at the collector of the horiz.drive. does it mean that the jungle IC has a problem?Check the horizontal vcc found 0volt.what voltage supply need to be check for jungle IC to function?Is it possible that the ic casuing short?pls advise..

    thanks,
    jojo
    from the philippines

    ReplyDelete
    Replies
    1. Hi Jojo, Thanks for your feedback, regarding the Sharp tv with B+ of 150 Vdc..this point to a problem on the feedback circuit..this include the Opto-isolator, the error amplifier and the related components.first check for dry joints around this circuit.that where you should focus on. for now don't worry about the jungle ic.

      Regards Humphrey

      Delete
  49. HI HUMPHREY
    thanks for your fantastic repair
    beh

    ReplyDelete
    Replies
    1. Hi Beh, Thanks for your input on this report..God bless you mightily.

      Regards Humphrey

      Delete
  50. Hi Humphrey,

    I have a CRT TV which when plug creates a whistling sound like time bomb.
    I checked on power supply board and here are the observations:
    1. voltage label that says 12V--> no voltage
    2. voltage label that says 5V --> OK
    3. voltage label that says 30V --> very low, like 12V
    4. voltage label that says 120V --> reads 40V.

    I double checked on (1), i found out that the input to the regulator that outputs 12V reads 3.5V.
    All voltage readings are referenced to the GND connection to where all the other voltage labels were located.

    ReplyDelete
    Replies
    1. Hi There. First I like your introduction words*****(whistling sound like time bomb)***** in electronics troubleshooting, human senses like sound, smell, sight, touch comes in handy...I can see you are using them to the maximum. With regard to this noise i recommend you go further and narrow down the actual component emitting this sound...must likely it will be the culprit...This usually point to a component which is at the point of dying or collapsing under full load.
      Voltage analysis: Again you have done a good job here. With regard to No1. I suggest you do further test here…remove the regulator from the circuit…if the voltage increases maybe the regulator is shorted. Voltage reading no:4: I believe this is the main B+ Voltage to the FBT, whenever you see this reading low this could point to a problem with power supply(primary) or the secondary side..To isolate the problem just lift up the middle leg of the H.O.T and power again briefly with you meter positive probe on the circuit board where you have removed the Middle leg of the H.O.T...If the voltage increases this means the primary power is ok and therefore you should concentrate on the secondary…last but not the least usually a FBT failing under load can give such a noise or the related component around the flyback transformer.
      Regards Humphrey

      Delete
    2. Humphrey, thanks!

      haha..yeah the sound seems to come from a transformer (not the flyback).
      yes! when the power supply board is connected--the sound emits, but when i remove the power supply board(main and power supply are in separate boards)--no sound.

      I checked also on switch mode IC (STRS6709), the BASE and COLLECTOR is shorted, evident when i removed the IC and check against datasheet, interchanging polarity of tester reveals same reading and that is zero ohm.

      I believe this is the culprit since, underserving the transformer. AM i right? If so, what are mostly affected by the busting of this IC as a consequence to other components?

      Thanks again. You are very generous of your knowledge.

      Reynel,
      Philippines

      Delete
    3. Hi Reynel,
      1. Something is not clear here…which transformer is making the noise? If chopper transformer then I expect the noise to be present even when the main board is separated.

      2. You said you measured the switch mode ic(str6709) and the base-collector is shorted…usually the base in internally connected and I wonder how you measured this pin.

      3. Again if there was output on the secondary side as per your initial testing then I don’t expect to have any output voltage if the switching ic (str6709) is shorted…

      Regards Humphrey

      Delete
    4. Hi again sir Humphrey!

      on (1)-> I dunno how you call the transformer but it is the one close to the STRS6709. The FBT is located on the main board. Yes, when i removed the connector between the power supply and main board--the noise is not present. And i tried to put my ears closer to the noise source and i think it is on the transformer (not the FBT on the mainboard).

      on (2)--> i measured strs6709 out of the board and using pin configuration on the datasheet. Reversing polarities of the Ohmmeter at x1 ohm range.

      on (3)--> do you think there are other culprit?

      Delete
    5. let me have the model of this TV asap

      Delete
    6. Hi sir!

      All i know it was a 32inch LG CRT TV.

      Delete
  51. In My sansui tv , the LED in the power supply is ON. when I click the remote button to switch ON the tv
    within a few seconds, the screen gets opened and closed . what will be the problem, please give suggessions.

    ReplyDelete
    Replies
    1. Hi there, the info given is not enough to make any conclusions...
      regards Humphrey

      Delete
  52. hi humphrey I need help on my TCL TV 21

    - Standby power (OK)
    - B+ voltage measures about 115 volts
    - high voltage (115V) reach to HOT collector but no voltage at the base
    - I check IC driver (115V)voltage on Collector but 0 Volt on the base
    - I replace all Leaky Capacitor in the power supply, (Pri & Sec) flyback circuit up to HOT
    - I also fix all dry joints on the PCB

    Here are my observation:

    - CRT NO POWER
    - IC TA8403K Vertical NO INPUT and VCC out
    - If i switch on the tV I heard a static voice the same with the normal one but no action
    - No sounds
    - If I push PTT Channel swich, I heard sound in the fly back

    I need your advice sir. thank you and god bless!

    ReplyDelete
  53. Not able to follow up the event happening here..did you say you hear chaa(static noise) when you switch on? then maybe High voltage is generated..therefore check if the screen voltage, RGB amp voltage, heater voltage is present.

    Regards Humphrey

    ReplyDelete
    Replies
    1. Thank you very much for helping sir. Theres a dry connection on the circuit of transformer on the secondary and primary side. so the tv now is working.. Thank you very much sir!

      Delete
  54. Hi Humphrey

    I need help on my dead 74 cm china TV set. HOT transistor was shorted and I have replaced it. Now b+ is only 19v and pulsating. Tested Secondary diodes nd are all ok . Voltage at the chopper collector is about 311v and pulsating . Replacing flyabk with a dummy load didnt change anything . Do u think the high frequency transformer could be the culprit? What is the expected voltage at the base of the chopper transitory?

    Thank you
    THOMAS

    ReplyDelete
    Replies
    1. Hi Thomas.

      Check for leaky/capacitors with high esr on the secondary side especially the B+ filter capacitor.

      Regards Humphrey

      Delete
    2. Thanks for your response sir, I don't have an esr meter so I replaced the following caps and checked new voltages on +ve leg of each:
      160V/220uf reading 19.5 v on +ve leg
      25V/2200uf reading 1.9v
      2 x 35V/ 1000uf reading 3.1v & 0.9v
      220v/47uf
      And 3 non polar caps rated 473k across the secondary diodes.

      Delete
  55. Hi sir I have a problem with the tv JVC14FTG . when i power on no power indicator lighted.I checked the mains cord,main cap,fuse they are ok.pls help

    ReplyDelete
    Replies
    1. Hi renjith, is the 320/155 v dc present at the main cap? is start-up voltage present? the above lesson is enough to get your tv up?

      Regards Humphrey

      Delete
    2. Sir i check the regulator BA51W12ST in JVC14FTG all pin measures 10vdc each except ground why? and i have a doubt of checking the start up volt is absent or present.and i noticed a white resistor 2W,27nj highly heated while power on.

      Delete
    3. This BA51W12S maybe may be shorted...replace it directly..for the white resistor 2W,27nj which is getting hot...i think there is no issue here, that is rated 2watts to take care of the heat.

      Regards Humphrey

      Delete
  56. Hi Humphrey

    I found a shorted zener diode on the secondary side along the +27v line and after replacing it the TV turned on but it was showing a single horizontal line at the center of the screen . I then checked the the voltages on the legs of the vertical I.c ( LA76141) and obtained the following readings :

    Pin1: 3.4v
    Pin2: 26.1v
    Pin3: 4.1v
    Pin4: ground
    Pin5: 0.09v
    Pin6: 27.1v
    Pin7: 2.8v

    I have replaced all the capicitors around this I.c and still nothing happens. I also noticed that's this I.c gets very hot quickly. How to test I this I.c is faulty?

    Thank you for your kind assistance
    Thomas

    ReplyDelete
    Replies
    1. Hi Thomas,

      First you have done a good job,Congratulations. If you have replaced all the capacitors related to this vertical ic...the next suspect is the actual I.C...unfortunately the best test for ics is direct replacement..further more you said it is getting very hot..another clue that this ic is gone.

      Regards Humphrey

      Delete
  57. Hi Humphrey

    Thank you for sharing your knowledge to everyone, may God bless you. Your blog is very useful indeed. Anyway I also have problem here that I would like to share with you. I tried to follow your method in an attempt to repair a dead 54cm tedelex EC2109i that I have at home. I managed to get the primary powersupply back on, courtesy of your volatge testing method. Here are my observations on the secondary side:
    - B+ is steady at 117v and is reaching HOT collector leg and the HOT is good
    -Primary transformer derives 117v, 18v & and they are all present
    - 5v , 9v & 24v are derived from FBT but all are very low at 0.09, 1.82 & 0.11v respectively
    -LED power light is flickering
    -RGB voltage is 117v & zero for heater
    -Volatge at the collector of horizontal drive transistor is 117v but this should be 49v
    according to schematic
    - Ohmmeter tests good on primary windings of the FBT.


    I dont know what to do next .Please advice

    Many thanks
    Bafana

    ReplyDelete
    Replies
    1. Hi Bafana, Thanks for your feedback,from what you have said you are doing very well. Now regarding your tv it seems the drive circuit is not working otherwise i would have expected the voltage at the collector of the drive transistor to go down to 49Vdc as you rightly put...but before i make this conclusion i have noted the power led is flickering...now this could point to shorted components and the most likely culprit from the story given here is the fbt...the bad news is that you can not be able to tell a good or bad fbt by using ordinary meter(ohmmeter)...in your case i advice direct replacement..

      Regards Humphrey

      Delete
  58. hello Sir I have a problem with my tv JVC14FTG that is it doesnot power on.I checked the mains cord,switch,relay,main cap,secondary diode, they are ok.I measure volt across main cap is 300vdc and i try the dummy load volt measured 110vdc .volt reaches the base of HOT. I measured volt in regulator BA51W12S.I found that there is only 10Vin but other leads shows 0 volt measure except gnd pin.why? is this is the reason for system doesnot turn on.......pls help

    ReplyDelete
    Replies
    1. Hi there, Besides this I.C.BA51W12S being a regulator it also act as over current protection, therefore if there is any short on the secondary side it will shutdown the tv...so i suggest you continue checking for sorted component on the secondary side..

      Regards Humphrey

      Delete
    2. i noticed the IC 78LR05 gets too hot why. is this ic short or the remote controller IC mn1873287 short which one is wright.and I also noticed vertical ic AN5539 has no input and out volt why?plss help sir.......

      Delete
  59. Hi, I'm Samuel I have a problem wit 21 inch crt Tv, when I switch on the power It ignite the screen and then go off, I've tried Everything in vain I've even changed the power IC STR W6754 but Still Behave the same It Only shows the power on Ignition and diapers later. The 400V capacitor is not discharging Even after the power is removed. please help

    ReplyDelete
    Replies
    1. HI Samuel, this could point to problem on the secondary side(a shorted component)
      regards Humphrey

      Delete
  60. I'll bookmark this site..
    Really helpfull for a newbie like me..

    ReplyDelete
  61. Hi Humphrey! Please help me, I am repairing a CRT Sony 21 TV, if I turn it on the power is in the standby mode but if I press the PTT Menu and volume the flyback is working for 10 seconds then it shutdown and it blinks 4 times.

    ReplyDelete
    Replies
    1. Hi Don, try to Google this error code****blinks 4 times*** for Sony and see what this error means...

      Regards Humphrey

      Delete
  62. Hi humphrey,

    I am very impressed with your thorough incite ,I am currently working on a faulty telly SEG CT 3250

    The problem is a Power surge.Tv doesn't turn on.
    -When I opened the telly I saw a burned fuse.I replaced it with another and tried tunring the telly and it burned.
    -The second thing I Immediately tested the transister and it showed it was faulty and tested the area around it. nothing else showed faulty.

    -3rd I have replaced the faulty transistor and a new fuse.I tried turning it on and this time the fuse didn't burn but the power Led is off,like there is no power.Then I have checked with the tester And the voltage is 314 on the capacitor(Power supply).Voltage also is on the IC.

    -4th I Changed the IC and the Outcome was now the power led is flickering but the tv doesn't turn on.

    Now I have checked and there is 67 Volt on the (output transistor).Is it a normal volatage?
    What shall I do next?I am running out of ideas.It has been more then 13 years since I've repaired a tv.Kinda forgotten how.

    MAny thanks,

    Ghassan.

    ReplyDelete
    Replies
    1. Hi Ghassan,

      You need to isolate this problem further using the method above on this article. Nb solder out the middle leg(collector) of the HOT and apply power and measure the voltage at that pin on the circuit board..if the voltage now increases to over 100 volts dc(b+) this confirms that the primary side is okay and you should concentrate on the secondary side.

      Regards Humphrey

      Delete
  63. hi sir..i have a question my TV have a noising sound what is possible cause?

    ReplyDelete
  64. your article is big help for me god bless you im chacha from tanzania

    ReplyDelete
    Replies
    1. Hi Chacha, Thank you for your feedback and glad to hear from TZ. God bless you too...

      Regards Humphrey

      Delete
  65. HI humphrey...thanks for your post, ive found it so helpful....do you offer any courses on electronis or something?
    Paul..
    SA

    ReplyDelete
    Replies
    1. Hi Paul, Thanks for your feedback and glad to hear from South Africa...regarding courses i am only offering ebooks on electronics repairs which are on sale on this blog.

      regards Humphrey

      Delete
  66. Hi Sir,
    I have PHILIPS 21" screen witch have problem, while i ON screen its working fine for few second, picture OK, sound OK, But after sometime its going OFF its self, again when i ON from PTT switch ON again and going OFF again, So if sir can kindly advice me in this problem.

    ReplyDelete
  67. Hi Tobgay, i suggest on check for faulty capacitors first in this set, both on the primary side and secondary side. regards Humphrey.

    ReplyDelete
  68. Hi.
    I have an Electrohome television set that makes a high pitched ticking/clicking noise when plugged in. The set does not turn on.

    Any help tips would be highly appreciated :>

    ReplyDelete
    Replies
    1. Hi Ken,
      Sounds like the set is being overloaded due to shorted component in there. i suggest you take it to a technician near your home town.
      regards Humphrey

      Delete
  69. hi, hunphery thanks for nice article

    ReplyDelete
    Replies
    1. Hi Prakash.
      Thanks for your positive feedback and you are very welcome here...

      Regards Humphrey

      Delete
  70. Hi, hunphery I am turely bless for your information

    ReplyDelete
    Replies
    1. Hi Tony,

      Glad to note that have been blessed by the information shared here. welcome..

      Regards Humphrey

      Delete
  71. Hi humphrey, can you help me to locate the possible trouble of my polytron tv 21SF76.I replaced the mosfet FS7UM and the unit is working with normal picture and sound. My only problem is the squealing chopper transformer,this chopper produces sound like cricket,it is very noisy.can you help me what to do for this kind of problem?

    ReplyDelete
    Replies
    1. Hi Jaime, Sounds like there is components around the fly-back which is about to fail, it could be the fly-back itself and therefore i suggest you check all the component around the horizontal output stage.
      regards Humphrey

      Delete
  72. Hi humphrey, can u help me to locate a serious problem with my 14inch crt tv. the problem is, each time i change the switch mode power transistor and fuse with a new one, and turns on the power, both of them keeps blowing out. i checked all the resistors and zener diodes of the primary side, they are all ok, what may be the actual cause, help me please...

    ReplyDelete
  73. Hi Purna, check the switching transistor/ic, posistor, main capacitor/bridge diode and any other component which has one leg on the live and the other leg on the ground(parallel)

    Regards Humphrey

    ReplyDelete
  74. Hi humphrey, thanks for the advice. It was really very helpful. The culprit was the main filter capacitor, it showed no meter reading when checked in ohmeter mode. I replaced it with a new one, along with other replacements.The set is all ok now. Thanks once again.

    ReplyDelete
  75. Peter
    Hi sir,I've a21" lg flatsreen tv which goes off after a few seconds.It had brown vertical ice and after replacing it,it goes on for approx 3 secs then goes off but stays on if I desolder the ice.I've tried different ICS but problem persists.please help.

    ReplyDelete
  76. Hi Peter, i suggest you change all the filter capacitors for the vertical circuits.
    regards Humphrey

    ReplyDelete
  77. Ben
    Hi, i think i have to congratulate you on your good blog, because obviously everybody is giving a good review about it.I have

    an issue with an LG MC-049B i did use a lot of good suggestions found on this blog but i'm still unsure about the IC STR-

    W6754 if it's faulty or not. I can't tell if it's it or another component. That's why i took all the courage i have left and

    decided to send you this message, hopping i'd find some helping hand or a good pieces of advise. The last time i checked the

    chassis i did the dummy load trick but unfortunately the bulb didn't light up so i concluded that there is something wrong

    with the primary side and i went investigating, the #4 leg "VCC" had 14.7 VDC which was under the minimum limit of operation

    start voltage, so i lifted it (the #4 leg) and surprisingly i found 74 VDC i'm chocked to say the least and i have no idea

    what to think about it. so what do you think, should i buy a new STR-W6754 or do further investigations. More suggestions are

    much appreciated, thank you.

    ReplyDelete
    Replies
    1. Hi Lalofa, Thank for your feedback, regarding the LG tv first you need to check if the start up vcc is present, in your case around 18 vdc is ok and the voltage at pin 1 should be around 300 vdc or 155 vdc(str-w6754)...you said you got 74vdc with the pin is lifted up...i doubt maybe you used the wrong ground(you should use the main capacitor negative pin as your ground in this case...or maybe you did not change the meet to dc mode and therefore used ac mode..please confirm that.

      For now concentrate on the primary side as you rightly put it

      by the way my name is Humphrey

      All the best

      Delete
  78. hi mr Humphrey! my samsung 14" colour tv audio would suddenly burst to huge noise. i suspected the tuner section. opened it and found that the main soldered point was broken. resoldered it and also resoldered the cold solder joints of two of the yoke coil joints. then turned the tv ON. since then, no raster, no sound! the standby led glows. on pressing the power button from remote, the led turns OFF, but nothing else happens. on further pressing the power button with remote, the led blinks. that's it..where could be the problem?? can tuner section disturb the eht drive?? i measured voltages at various points..B+ 135V (125V printed on ckt board), auxiliary supply, 3, 5, 8V from multi regulator ic. also, 11V from smps to multi reg. ic, sound ic,and eht driver transistor collector.

    ReplyDelete
  79. hi pd

    Sounds like there is something which went wrong when re-soldering the dry joints and you ended shorting a component or a track...just re-trace what you did and undo what you suspect went wrong...
    regards Humphrey

    ReplyDelete
  80. hi Humphrey,
    Thanks for the good job.my TV takes a very long time to switch on nowadays.its an old sony.the sound is good but the pictures take around 20-30 seconds to show.once it shows,it continues ok.the long delay is only there when the tv stays for long when switched off.otherwise if I switch off then on again,it doesn't need warm-up.what could be the problem?
    Simon.

    ReplyDelete
    Replies
    1. Hi Simon,

      This can point to lots of dry joints and capacitors faulty.

      regards Humphrey

      Delete
  81. Hi Humphrey please help me with my China Board for CRT TV model. Standby LED only ..

    Check the following:
    B+ = 110 volts
    Voltage on HOT using D1555 collector is 110 volt
    High voltage reach to CRT Neck: 180 volts
    12 volts on driver transformer = present
    voltage on driver transistor collector = present
    voltage on driver transistor base = no voltage present because the circuit is connected to ground line up to negative capacitor before jungle ic.

    I'l almost change the following:
    Flyback
    memory 24c08
    re solder Jungle IC pin, and all dry joints in horizontal out & try pressing the remote/ key channel up & down to fire up but still not working.

    I am interesting to buy you ebook but how?

    tnx and god bless!

    ReplyDelete
    Replies
    1. Hi Rey, use a remote control to fire the TV on...seems like just sleeping.

      Regards Humphrey

      Delete
  82. sir in my onida tv the power led light is not on i change fuse in tv but there is not working what is the problem please help me

    ReplyDelete
    Replies
    1. Hi Deena,
      The info you have given i not enough for me to make any conclusion, is the fuse blown? did it blow again after replacement? if so change the control ic or switching transistor on the primary power supply also...
      all the best Deena
      Regards Humphrey

      Delete