Dead CRT TV brought back to life and how it snubbed my nose!
I got one Nikai NTV2102 with the complaint that it went dead after seeing only a vertical line on the screen, subsequent to which even sound went off.
So, no light and sound! As usual, I opened the set and did a thorough cleaning of inside, keeping it out on the Car Porch, with a blower and set of brushes. I noticed that one 220uF/160V was bulgy on the top in the B+ line that goes to FBT (LOT) and HOT. Took it out and see, what it measured:
Replaced the capacitor. Since the fuse was intact, and there was no further visible damages, except burnt dark marks in CRT PCB as well as around FBT and SMPS areas, where dropping resistors are used, I connected the TV to mains and switched it on. It came on but with a 1″ gap at top and bottom, indicating problems elsewhere.
So, disconnected the PCB after discharging the anode cap, and started probing for the ‘culprits’! (I did not suspect anything wrong with the vertical IC, though the CTV was reported to have died after a vertical line, as the SMPS was starting, LED light was glowing, no fuse was blown, and there indeed was a raster though slightly narrow and further I had checked for any shorts using my analogue multimeter. The ring test on the yoke also showed no fault)
Checked ESRs of capacitors in the SMPS, around FBT and CRT PCB. Changed all capacitors which were found with its ESR value crossing the limits. Did a thorough dry solder patch up and board cleaning. Removed the jumper wire that goes to the Horizontal Output Transistor (HOT), and connected a 100W bulb as a load, connected to mains and switched on. Nothing happened! The set was now completely dead! By trying to be a very ‘smart’ technician with a lot of confidence and handling things so easily, with varieties of testing gadgets and methods with me, I got a snub on my nose, perhaps the CTV would have smirked, if it could!
So, after taking a break to play some games in the computer, I turned back my attention to the TV. Checked fuse and then ensured that B+ voltage at the Tank Capacitor was there. Yes, it was reading almost 280VDC. This set was using a 330uF/400V capacitor in its SMPS. Discharged the capacitor. Used my Ring Tester on the SMPS Transformer and noticed that it was lighting upto the yellow LEDs and not full. Well, that could happen as all the Transformers would not show all LEDs lighting up due to its load on the secondary, and the feed back circuit on the primary. This SMPS was using IC TDA16846P as its PWM controller, with IRF840 mosfet as driver. So, checked all components in the SMPS primary one by one. Noticed that one resistor was showing a funny reading! The colour band indicated Brown, Green and Red, for a 1.5K resistor. But see the reading, it was showing 7.46K.
Checked all the diodes and other resistors and capacitors by pulling out one end of it! (I had already replaced all electrolytic capacitors except the Tank Capacitor in the SMPS primary and secondary section) All else were OK! So, replaced the resistor, and with the feeling of a Police Inspector, who caught the thief, I switched the CTV on, but, again, nothing happened! It remained dead, or shall I say, deader? Another chance for the CTV to smirk! Another vexed snub, and another round of games in computer!
I continued my probe for the fault on the next day, starting fresh. Removed the SMPS transformer this time. Checked it with ESR meter as well as Ring Tester. It was ok. Checked all the secondary diodes and components by pulling out one end. OK. So, removed the mosfet, and connected an Universal Module and switched it on:
This proved that the Secondary side and the SMPS Transformer primary winding were all ok. Removed the PWM controller IC and placed a 14 pin socket in its place. Replaced the Run DC diodes, as suggested by Jestine Yong in his SMPS repair book. Replaced a few resistors and capacitors in the primary side, doubting probable failure in load. Connected the SMPS transformer and put back the IC, checked again. Same result, CTV’s smirk darkened further! While checking live again, wrongly shorted the IRF pins and the fuse blew and mosfet got dead short! Got new IC and mosfet and put it in. Switched on, nothing happened, it remained dead. Looked like it got habituated in it! But see my plight, every time I have to discharge the capacitor, disconnect the mains and continue to probe, by tilting the board to both sides, causing strain on the LOT and CRT wires and board. After some time, I got accustomed to this process, and it looked like some sort of exercise for me and I was rather amused in it and enjoying!
Forgot to mention that when things were going out of control, I had downloaded the datasheet of the IC, studied the function of each pin and the minimum voltages that should be present for proper functioning. I even drew a circuit of the SMPS by looking at the board on both sides, and noted the minimum and maximum of voltages at various pins of the IC:
Continued my work on the CTV on the third day! Well, was I getting fatigued by the tough fight by the CTV? Well, perhaps! This time, I rechecked all the capacitors replaced with the one on the board. I do this by putting a mark on top of the capacitor on the board, when a matching removed one is found and finally count both replaced and removed to tally. Traced that I had put in 4.7uF/25V in the SMPS primary, in place of a 47uF/25V!!! This was to pin 14 of the IC, where the + power supply is fed from the start up resistor and then from the second primary winding of the SMPS. (Incidentally, this circuit does not use an optocoupler and no feed back goes from the secondary to the primary. So, during my failed attempts in the earlier rounds, I had tried keeping only the bulb load to the 110V B+ and disconnecting the other two diodes from the secondary side.) Replaced the capacitor. With no hope, switched the CTV on, with the same result, but no disappointment for me this time, as I was seasoned now! Bought two more ICs from different shops with different batch numbers, thinking that the one bought by me could be a fake. Replaced the IC. This time there was a change! The output pulsated slowly on, off, flip-flop, and though this is an improvement on the situation, the efforts were a flop! So, resorted to replacing the tank capacitor with a new one, replacing the run DC diode once again, as suggested by Jestine Yong in his book. Same result! Replaced the IC again from a different batch! Same result! Rechecked all the components in the primary side once again for a possible failure again! Nothing at all! What to do now?
Continued my work on the CTV for the fourth day! By this time, I was like a warrior whose energy is all used up and continuing his fight for the sake of it! Look at the defective as well as suspected components replaced by me! All these look like soldiers who lost their life or given compulsory retirement, in a battle! The cover you see is that of the Universal SMPS Module that I used for checking.
Finally, on the 5th day, I decided, this is it, no more nonsense! So, I concluded either it is due to fake ICs or the problem in the second feed back winding on the primary of the Transformer. So, decided to take off the IC and Mosfet and connect the Universal Module in its place. Temporarily connected it and after restoring all open jumper wires and other connections, connected the board to the CRT and switched on. It worked just fine! So, discharged the anode, disconnected the board and fixed the universal module firmly on the heat sink of the mosfet, and reconnected the board to CRT.
Switched it on, it worked well. Adjusted the brightness, contrast, colour and sharpness to a pleasing level. See the pictures below:
I tested the CTV for 5 hours continuously on that day and again for several hours today. It worked very well! So, did I win the battle, but lost my pride in a truce? Well, it is for you all to decide the climax of this CTV story!
This article was prepared for you by Parasuraman Subramanian from India. He has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company and presently working as Consultant Manager, Purchase & IT, in Irinjalakuda Cooperative Hospital.
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https://www.jestineyong.com/ac-power-adapter-repaired/
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Merlin Marquardt
November 30, 2015 at 12:03 pm
Big repair! Great work!
Yogesh Panchal
November 30, 2015 at 2:49 pm
Sir, Salute to your patiance and Passion Congratulations!
Albert van Bemmelen
November 30, 2015 at 3:57 pm
Thank you for this nice repair with almost biblical proportions. As you only left out the "on the sixth day... and seventh day". Anyway you really deserved the resting day after this successful repair!
joop
November 30, 2015 at 7:31 pm
Hell of a job. But fine article.
Thanks
Robert
November 30, 2015 at 7:49 pm
Wow Parasuraman! As well as your comprehensive electronics knowledge, this is also a study in determination, patience and resolve.
Well done that man!
Kind regards
Robert
Bernie Scott
November 30, 2015 at 9:32 pm
Wow...Fantastic job there.....These tough ones can really ruin your day...keep up the good work.....
Amendar
December 1, 2015 at 12:12 am
Good job,
Happy you made it work.
Would you supply specification/datasheet of this "Universal Module".
It will be great if include some explanation.
Thank you
Parasuraman S
December 3, 2015 at 10:35 am
Unfortunately, there are no specifications. This is available in the local market and costs only Rs.110/- per piece. The manufacturer has scraped the number of the mosfet in order to prevent copying! The module is built around 3842 PWM IC. It has a small smps transformer for run DC. In a couple of cases, I have found that this IC fails after a few days of working. So, I replaced all the 5 electrolytic capacitors while replacing this IC. Then it never failed again!
Lawrence Pina
December 1, 2015 at 12:20 am
In my experience, technician-induced problems on CRT TV/Monitor boards generally indicate a solder pad which has lifted and separated from its trace. The joint looks good, even under magnification, but the track is open. Pressing with test probes (while checking for continuity) generally reconnects the pad to the trace, so the only way I've ever been able to find and fix these things is to vacuum desolder everything I've touched (and anything anyone else has touched) and physically nudge each solder pad with a toothpick to see if it moves. This method doesn't always find a disconnected pad but I do remember several cases where that was the problem.
Parasuraman S
December 3, 2015 at 10:40 am
As you might have noticed from my elaboration, I had indeed removed all components from the primary side, which means the solder was sucked and removed. Then I had checked for any track cuts, though this was done earlier after seeing no component failure, using ESR Meter, which is a very reliable and accurate low ohm tester. Used X10 Magnifying lens also to check the track! But never tried the toothpick method, as this is new to me. I have a PCB poker and I looked for any strained contact joints. Many thanks for your valuable suggestion.
Andre Gopee
December 1, 2015 at 2:39 am
I Must say your determination is something to desire. As I always say if at first you don't succeed, Try and try again and every once in a while take a break. it always helps. Thanks for sharing your experience.
ifa
December 1, 2015 at 5:10 am
sir, in your busy schedule i think you've done a great job. god bless you.
Robert Calk
December 1, 2015 at 10:46 am
Good job getting the TV working, Parasuraman. I was thinking the problem was a broken track somewhere also as Lawrence Pina mentioned.
vishn.b.vijay
December 1, 2015 at 12:56 pm
You were don a Perfect job.and thankyou to sharing.
Kosta
December 1, 2015 at 7:07 pm
Great repair and case studie! Thank you!
Paris Azis
December 4, 2015 at 3:12 am
Hello Parasuraman
I am impressed with your dilemma about the final result, at the end of your text.
I’d only like to reassure you that you certainly won the battle (the set is already repaired and that’s all what’s needed) and what’s more, you didn’t lose any pride at all! I just don’t see any connection between personal pride and a repair anyway…
Best Regards
Parasuraman S
December 5, 2015 at 9:57 am
I am a hobbyist in electronics and am not a commercial guy. I do not depend on earning from my service income and do not aim at it. It is a thrill to service a set and get a successful result. The joy one gets when one has brought back a set to life and more importantly to its 'near perfect' condition, is inimitable and it is a blissful experience. For me, it is always a challenge and I take it that way. I am a typical emotional guy, who feels very happy when a set is repaired and I see a glint of happy flash in the eyes of the customer. This is similar to the satisfaction of a doctor, who feels great after a successful surgery. On the contrary, when I fail to derive this 'complete' satisfaction, it gnaws my heart! There are a few customers who call me even months later to express their gratitude and how their entire family remember me, when their sets work very well! That is the fuel I need to keep me going, and not money! Moreover, I wrote the article with an emotional touch of a melodrama, to break the monotony and make it more interesting to read! So, kindly bear with me!
Paris Azis
December 5, 2015 at 6:29 pm
Hi Parasuraman
I fully understand every single word of your answer which also sketches perfectly your profile and I fully agree with the meaning of it, with only one exception which I see again in your answer, that phrase ending with “it gnaws my heart”. And this was (and is) my point. You must (please take it exclusively as a friendly proposal) drop this notion in the garbage bin. There is no worse obstacle than that when we perform our professional tasks (especially when you state that you are a hobbyist). If you feel that you lost perfection (which is acceptable but nevertheless quite different and in any case irrelevant to personal pride) in this repair just because you used a modification instead of finding what was wrong with the original PWM IC, then, very simply, think about how many “professionals” could bring the result you brought and comfort yourself! This will furthermore eradicate any similar thoughts of your mind. I am also emotional but as much as I can I permanently try to use my logic as a filter about these things.
Finally I have written you my first comment on the exclusive purpose to support the notion of the need for all of us involved in electronics to eliminate this awful thought (which only generates disappointment) and let our imagination to work freely when troubleshooting (which instead effectively leads us to the proper solution we need each time).
All the best to you
Robert Calk
December 6, 2015 at 7:18 am
I agree with both of you. The motherboard that I replaced in my friend Michelle's laptop (that was a pain in the neck) only lasted about 7 months. The after-market suppliers are untrustworthy. So from now on I'm not going to touch laptop motherboards because they are just not worth the trouble - it's cheaper to buy a new laptop.
I replaced the power button board and input power board because they are inexpensive to see if maybe they were the problem, even though I couldn't find anything wrong with the original boards. The ribbon cables were good also.
I'm currently checking individual components on the motherboard, but only just for the experience and fun of it. Of course, It would be a total waste of time if I were trying to make money. She is buying a new laptop, which is what I suggested that she do from the beginning.
Paris Azis
December 6, 2015 at 7:53 pm
Hi Robert
Thank you for your complementary intervention. I think that we have enough stress originated from plenty other really serious and unavoidable causes during our everyday life which we must confront with and we just need to get rid of such additional burdens that we ourselves put on our shoulders… On the other hand all we can control is just our thoughts and nothing else…
A failure in repairing an apparatus (if good will and respect to the customer is always there) is neither the end of the world or a loss of a human life as it happens with surgeon doctors. We are performing similar tasks but in human made machines and this is quite different criterion.
Thanks again
Robert Calk
December 7, 2015 at 6:22 am
Hi Paris,
The problem is just that companies selling motherboards are completely unreliable - it's as simple as that. If you read my articles then you know that one company sold me a damaged MOBO, and another company sold me one that was no good at all. Then now, the one that worked, only worked until the warranty expired. All of them claimed their MOBO's were brand new, when I could clearly see that they were refurbished! So all of them I have experience with are liars and crooks.
But, it's not a total waste: I offered to buy the new 1T Hard Drive from her to use as an external backup; and I gained a lot of experience too.
Paris Azis
December 7, 2015 at 9:31 pm
Hi Robert
Unfortunately these things you refer to are happening. Given that we cannot do anything so radical in order to eliminate or even only to reverse this bad behavior, the unique choice we have is to find new suppliers.
However my point was not exactly that. In any case one must remain cool and calm under similar situations and especially as regards repairs I feel that the key criterion about them is if a repair is completed successfully (regardless the possibility for the repairer having been forced to modify the circuit).
In other words if a repairer does all he can do and the final result is a working apparatus, he is already honest against himself first and against the owner of the apparatus as well. On the contrary if the repairer cannot (for any reason) repair the apparatus and he purposely manipulates it in such a way rendering it irreparable by anyone else after him in order to keep intact his pride or reputation or name it as you like, then yes, time will come and he will certainly suffer its loss. This can also happen very soon, if his customer somehow gets informed about what happened, but finally this is all natural to happen and doesn’t surprise me at all.
Greetings!
Robert Calk
December 8, 2015 at 4:00 am
I'm always calm and cool. I'm not wasting anymore of my time looking for a better computer motherboard supplier. It's not worth the trouble. She is buying a new laptop that has better capabilities and features than her old one had for less than $300US.
Parasuraman S
December 6, 2015 at 12:35 pm
Very nice 'peace' of advice and I really appreciate your concern. I usually recover from the sullen mood soon and get back to my work with the vigor and enthusiasm necessary for a trouble shoot. You are very right in your observation and I shall take your advice in the right perspective and practise implementation. Please do correct me like this, whenever I go astray, which will help my self-transformation efforts! Thank you once again!
Paris Azis
December 6, 2015 at 7:23 pm
You are always welcome Parasuraman.
Now you’ve got it! So, no more sullen mood even for a single minute and that’s all and if such a mood insists, just think of those “few customers who call you even months later to express their gratitude”…
No need to wonder about if there is any other “sullen mood extinguisher” more effective than this one and you already earned it! Just let it work for you!
Greetings
Ulises Aguilar Pazzani
December 5, 2015 at 1:20 am
Great Job Sir very nice explain
rasheed
December 17, 2015 at 2:12 am
sir please give me the LOT code number of nikai NTV-2102.
I have one for repair but there is no number on FBT. pls help.
rasheed.
Jestine Yong
December 17, 2015 at 8:09 am
Hi Rasheed,
Sorry I do not have the info. You need to look for the service manual to find out the number.
Jestine
Parasuraman S
December 17, 2015 at 9:00 am
Dear Rasheed:
I do not have the schematic of this CTV. I did not note down the number and the CTV has already gone back to the customer after repair. I can help you only if and when it comes back. First of all do a test with Ring Tester and ensure that the LOT is really gone. Then if it is defective, use Blue ESR Meter and check the ohms between each winding, and make a note. The correct method is always to check the inductance, but you need an accurate test equipment, a cumbersome procedure to do it. Generally, this is what we do. Then go for an exactly matching LOT from the market. Sometimes the guy in the shop may also help you. I am sorry, I could not help you! All the best!
rasheed
December 17, 2015 at 11:14 pm
hi sir.
actually the problem is HT wire sparking all around with cracking noise.
Parasuraman S
December 25, 2015 at 10:59 pm
Dear Rasheed:
For HT arcing from the wire can be solved. First of do a thorough cleaning preferably with denatured spirit from the stem where it goes inside the lot, to the anode cap. Do the same around the stem area also. Then pull the clip side of the wire through the anode rubber cap about two inches. Desolder the clip that goes inside the CRT anode. Remove the rubber cap. Do one more cleaning. Then locate suitable sleeve of any cable or two wheeler petrol tube. Insert the punctured red wire into this upto the stem. If it is not tight enough, you may have to cover the entire wire with a black tape and then insert it into this tube or sleeve. Then cut the tube at the anode side to the extent that you are able to put back the rubber cap and resolder the clip. That is all! There won't be any arcing for sure. I have done this on many TVs!
Ivan
May 20, 2020 at 3:01 am
Congss sir, congs