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.
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.
For those who want to be expert in Switch mode power supply(S.M.P.S) repair i personally recommend this book by Jestine Yong...i have personally read it and added a few tricks to my arsenal..click on the book for more info on how to have it on your workbench.
thanks for sharing this information. Waiting for more :)ReplyDelete
Keep up the good work.ReplyDelete
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.ReplyDelete
Great work, very useful informations,ReplyDelete
hi nameless...thanks for your encouraging words.. wish you the best.ReplyDelete
good article. thanks for sharing.ReplyDelete
Thank you for visiting us & comments mr Nugroho...ReplyDelete
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
let me have a detailed behavior of this TV via my email given elsewhere on this blog.ReplyDelete
hi sir,can i have your email add please so that i will send u details regarding in my panasonic televesion...ReplyDelete
My email is on my profileReplyDelete
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
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.ReplyDelete
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.ReplyDelete
Thank you very much for sharing your works.
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.ReplyDelete
kind regards Humphrey
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.ReplyDelete
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.
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 humphreyReplyDelete
Thanks and welcome kind regards HumphreyReplyDelete
hello sir, i have JVC model AV-20NT11ReplyDelete
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
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.ReplyDelete
btw, i didnt found any defective components yet, but i did replaced those components mentioned above but still no luck..ReplyDelete
thanks for reply sir HumphreyReplyDelete
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
email me at: email@example.com for details of this repair. if possible include pic and let see how it goes.ReplyDelete
Kind regards humphrey
i had repair sharp tv 21inch but the problem theres a sound but no picture can yuo give an idea of this trobol sir humphreyReplyDelete
Hi..is HV present? heater is lighted? screen voltage 300 vdc? is there something on the screen of just blank screen?ReplyDelete
see this link for more info...
Another great, well written, & very practical, "how to" article from a very helpful person.ReplyDelete
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.
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.ReplyDelete
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)
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
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.ReplyDelete
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
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?ReplyDelete
For the flyback to work it will require the two circuits mensioned above to be working otherwise it will not work.
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.ReplyDelete
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.
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.ReplyDelete
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.
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 bestReplyDelete
I dont have an ESR meter. I only use my multimeter to test capacitors. Would this be enough?
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?
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.ReplyDelete
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.ReplyDelete
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
Thanks for your positive feedback, May God bless the work of your hands too.
I need more example with pics on cold and hot areaReplyDelete
For more info on this and much more consider investing on this book on CRT Television repair course.Delete
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...ReplyDelete
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?
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.Delete
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
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?Delete
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.
James from Philippines
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 icsReplyDelete
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).ReplyDelete
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
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?Delete
I have learned a lot while reading this.
Thank you very much.
Hi Chris, Thanks for your feedback..you are most welcome.Delete
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?ReplyDelete
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?
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..
from the philippines
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.Delete
thanks for your fantastic repair
Hi Beh, Thanks for your input on this report..God bless you mightily.Delete
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.
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.Delete
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.
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.
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…
Hi again sir Humphrey!Delete
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?
let me have the model of this TV asapDelete
All i know it was a 32inch LG CRT TV.
In My sansui tv , the LED in the power supply is ON. when I click the remote button to switch ON the tvReplyDelete
within a few seconds, the screen gets opened and closed . what will be the problem, please give suggessions.
Hi there, the info given is not enough to make any conclusions...Delete
hi humphrey I need help on my TCL TV 21ReplyDelete
- 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!
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.ReplyDelete
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
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?
Check for leaky/capacitors with high esr on the secondary side especially the B+ filter capacitor.
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:Delete
160V/220uf reading 19.5 v on +ve leg
25V/2200uf reading 1.9v
2 x 35V/ 1000uf reading 3.1v & 0.9v
And 3 non polar caps rated 473k across the secondary diodes.
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 helpReplyDelete
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?Delete
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
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.Delete
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 :
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
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.
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
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..Delete
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 helpReplyDelete
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..Delete
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
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 helpReplyDelete
HI Samuel, this could point to problem on the secondary side(a shorted component)Delete
I'll bookmark this site..ReplyDelete
Really helpfull for a newbie like me..
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
Hi Don, try to Google this error code****blinks 4 times*** for Sony and see what this error means...Delete
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.
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.
hi sir..i have a question my TV have a noising sound what is possible cause?ReplyDelete
your article is big help for me god bless you im chacha from tanzaniaReplyDelete
Hi Chacha, Thank you for your feedback and glad to hear from TZ. God bless you too...Delete
HI humphrey...thanks for your post, ive found it so helpful....do you offer any courses on electronis or something?ReplyDelete
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.Delete
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.
Hi Tobgay, i suggest on check for faulty capacitors first in this set, both on the primary side and secondary side. regards Humphrey.ReplyDelete
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 :>
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.
hi, hunphery thanks for nice articleReplyDelete
Thanks for your positive feedback and you are very welcome here...
Hi, hunphery I am turely bless for your informationReplyDelete
Glad to note that have been blessed by the information shared here. welcome..
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
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.Delete
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
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)ReplyDelete
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
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.
Hi Peter, i suggest you change all the filter capacitors for the vertical circuits.ReplyDelete
Hi Humphrey,i have samsung TV 21" model ct21a530f.The problem is when i turn ON the set it displays picture at about 4" long,BUt have a sounds after 5 sec it turns power off and ON repeatedly...i check Pri and Sec power supply voltage is present (300VDC) @ main CAP...Can u help me with this?Delete
Hi Humphrey,i have samsung TV 21" model ct21a530f.The problem is when i turn ON the set it displays picture at about 4" long,BUt have a sounds after 5 sec it turns power off and ON repeatedly...i check Pri and Sec power supply voltage is present (300VDC) @ main CAP...Can u help me with this?Delete
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.
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.Delete
For now concentrate on the primary side as you rightly put it
by the way my name is Humphrey
All the best
Hi Humphrey, i'm still struggling with this LG-TV, so please bear with me. the reason why i didn't get back after your answer, is because i was disgusted, i got discouraged and left it without repair, after a while i did some recherche and tried some tricks and finaly i got the B+ 110 Vdc(btw it was the photocoupler, i changed it and B+ was there), but now the TV still dosn't work and i don't know what to do next so please help me out. PS:when i put the chassis back on tv, i mesure the FBT there are neither -14 Vdc nor +14 Vdc, and sometimes the breaker goes off (no electricity in the room).Delete
If nothing is happening at the flyback maybe there is a problem with drive circuit...Delete
thank you for your quick reply, last time i was reading one of your excellent tutorial and i got this rule: "if the filament is lit than the FBT is working", in my case it is. but the other voltages are absent (28, -14, 14.. ), and there is another problem in my investigation i opened the socket and the screen wire came out i put it back but it is loose i don't know if it is important to put it back and make it stand because inside the socket this wire touches nothing and the same goes for the focous wire( i mean it doesn't came out but it touches nothing)Delete
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
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...
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?
This can point to lots of dry joints and capacitors faulty.
Whay a nice article!ReplyDelete
Hi Humphrey please help me with my China Board for CRT TV model. Standby LED only ..ReplyDelete
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:
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!
Hi Rey, use a remote control to fire the TV on...seems like just sleeping.Delete
thanks for sharing the information.ReplyDelete
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 meReplyDelete
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
sir my onida 20" (xs dlx) tv is dead by a thunder, so i replaced transistor "D1802" and main capacitor "220/450V" on main power section area but no use, so i changed the horizontal output transistor "D1426" also but still no use. after changing all these i checked the volts in main capacitor and its reading is 300+ VDC. what i want to do now? in this circuit i searched for power regulator ic to measure the vcc-IN volt (as you said) but i dont know which one is power regulated ic in this circuit! there are 3 ic's in this circuit and they are 1) AN5522 (7 pin, i think it is vertical ic) 2) TDA2616 (9pin i think its for audio) and 3) 24c16w6 8pin, is it was the power regulated ic?ReplyDelete
Check out his article on how to solve power surge problem...Delete
Hi sir humprey I have learned a lot while reading this.thank you.and please help me sir with my 14inches crt tv model TCL-14276 standby led only B+ =90vReplyDelete
What happen when you switch on the set using remote? let start from there...Delete
very nice circuit pic....thanks for the post.ReplyDelete
Thanks and welcome DavidDelete
Hiiii sir I have LG CRT TV 21'' & thats tv is power LED is not ON & I am checking fuse will be blown I have change this but this is again blown . What is defect is created in tv on primary side ?ReplyDelete
Please help me
Hiiii Amit, Rarely does the main fuse blow alone, there must be a cause which is usually a shorted component on the supply, the most likely culprit is the switching component on that supply(eg control ic) all the best.Delete
Hi Humphrey good day! Please help me with my CRT Universal China Board i'm trying to put into 21 inches picture tube tv because its original 14 inches tube is broken. So I was planning to put the board into 21 inches because its the same CRT socket. After I installed picture is OK but i notice that the vertical size not complete. I'm trying to repair the remote control of this board but i failed because its totally damaged . Where can i start here? This universal China Board is using LA 78040 vertical Deflection IC. How can I buy your ebook? Thank You and God Bless!!..ReplyDelete
Hi Adonis,To set the height you will need to use the remote which came with that universal board, but still it will not fill the whole screen height wise since the board is 14 inch...all my books are instant download upon payment and therefore you can go ahead and order.Delete
Hi Humphrey, I am Sumith, Please help me to sort out the over oscillation problem in 21'' flat Onida Black TV.Once I have changed Horizontal out put Transistor which is already in shot condition, new H out transistor also blown.I have noticed that B+ voltage is 144v. Is it normal,i think its B+ is 135v. But it don't have any 135 v regulator in secondary side of SM Transformer.its LOT is ok. If B+ voltage is problem,how can i rectify this plz help me ..ReplyDelete
Hi Sumith, that sounds like regulation problem, check the feedback circuit and the place to start with is the opto isolator.Delete
I need the chopper transformer employed in Sharp 29FN1 TV. I have not been able to source this part locally here in Nigeria. Kindly assist.ReplyDelete
Hi Joe, i don't have this fbt, besides even if i have it, sending it to Nigeria will be very expensive and therefore not economical.Delete
hi sir.please help me troubleshooting sanyo 21inch.the problem is that when i press the volume,the channel change.sometimes its ok but mostly not.also when i press the channel the volume goes down or up.ReplyDelete
please help me sir
First do first aid on this tv by re-soldering all dry joints.Delete
Thanks for this amazing article.
My LG Flatron Tv doesn't get ON through main supply, the led is On.., but when I power the tv through the Tv's front end power switch, it works. In between, If somehow the main supply is disturbed, I have to power the mains then wait gor like 5-10 mins then pressing the same power switch provided at the front end, then it works. Please help me
Hi Kumar, sounds like the power ON switch has a problem.Delete
Thanks and welcome AshokDelete
Hi Humphrey, how can i buy your e book CRT TV REPAIR COURSE. I don't have any bank cards. ThanksReplyDelete
You can contact me at my email firstname.lastname@example.org
For my details so that you can use western union agent near your home town
there sir , it is very fine post ,please publish the blog in "bangla" thank you so mouchReplyDelete
Checkout google translate toolbar on the right side of this blog to translate this page.
I am learning in CRT TV repair. I have been read many discussions in your site from start to the end. I got various information about of CRT TV in your sharing discussions.
Thank you very much to Humphrey and all.
Thanks for your feedback and glad you find my blog useful..all the best Neglay.
I m very Impressed with your blog.
I have Lg flatron crt t.v. it was not getting on.led was not glowing.I found blown fuse and burnt main capacitor 330mf 450 v. I replaced it with 220mf 500v capacitor.but when I put my t.v on it trips my main supply cb and blows fuse.
I removed str w6754 but nothing happend.please reply soon.
Change the STR W-6754,Delete
I have problem with Samsung CRT TV.
standby led blinking 5 time n TV not work. what is reason?
Hello sir when I put a new 3amp fuse it blown suddenly just switch on power supply..so how can I check where is the fault..plz reply me ..abhijit from india.ReplyDelete
Hello sir my onida tv oxygen thunder model fuse blown 3.15 amp .,when I changed a new with 3 ampbagain fuse blown already I ve changed 3 times but problem not solved what I have to do nowReplyDelete
my television stops working after lightning stroke.. pls helpReplyDelete
i didnt get how to attach dummy loader..
good eve sir...pwedi magtagalog dito?ReplyDelete
sir pwedi tagalog ang salita?ReplyDelete
Hi sir! I'm troubleshooting china tv . I measured B+ i got 12v but when i lift up resistor in B+ line i got 110v solder back the lifted pin and remove HOT igot 110v .what could be a problem?ReplyDelete
Good day sir humphrey, i have a question about to my friend crt tv 21'' jvc that the red light led is blinking. what is the common component is fault or problem?ReplyDelete
Hi MJ, this point to some overload in the system(overload here mean something shorted in the system) and hence does not point on the actual circuit.Delete
Hello Humphrey, I was wondering if this process would work on our tv as well. We have a toshiba crt tv model cf36g55. For a few years the picture would randomly go out but smack the sides and it was fine for a good bit. Lately it's been turning off and we have to unplug, smack, plug back in and repeat until it turns on. The spot to smack is the lower right hand corner by the power button. I've read that with the blinking light it's going into standby mode and the power supply is going. I don't want to replace the set if it's a fairly easy fix. This is the only site I've come across that has the diagrams even slightly close to the set we have. Any info or feedback is appreciated. Thank you!ReplyDelete
The tv seems to have lots of dry joints, open the set and re-solder any joint which look loose and there you go...no spare part required.Delete
A great article that emphasizes on the most important testing points on switch mode power supplies! I'm impressed by this long comments section. Humphrey, you're a gem among the stones of electronics repair industry. Wish you a long and prosperous career!ReplyDelete
Crt sanyo dead where to goReplyDelete
I'm job. hi Hamphrey,my lg TV is showing many thin horrizontal lines at the top of screen about 1and half inch thick.what could be the course.ReplyDelete
Im job.my lg CRT TV shows thin horrizontal lines at top of the screen about 1 1/2inch thick.what could be the cause?ReplyDelete
hello,there is horizontal white line when tv is turned on,but i have a problem locating the horizontal ic on my board.the name on the tv board is tehlikeli canli bolge,please can you helpReplyDelete
My crt 21inch tv blows fuse and power transistor seconds after switching it on.what could be causing this?please show video of what to check or change.thanks in advance.ReplyDelete
A 14 inches sharp CRT TV indicates red light when I switched it on but does not show anything on the screen. Pls what do I do?ReplyDelete
Hi Sir I have a sansui crt tv when I put it on it just show a vertical line . I changed the vertical IC, 25v 1000uf capacitor, 35v470uf but still no change. What can your advice on this one?ReplyDelete
Vertical line? That is caused by failure on horizontal circuit. Obviously something is open.Delete
EHT number kato?ReplyDelete
Hello sir how do I join this page? Or am I there already ? Thanks GeorgeReplyDelete
Hello sir.my 14"crt tv b+ 110 ok but, heater not growing,l have already changed vertical transistors and horizontal ic . But there is no 180v on fbt.please I need your assistanceReplyDelete