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Is it necessary to power on in order to diagnose failure IC of CRT TV?

bshi02

Mar 7, 2024
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Hello.

A few days ago,I stumbled on A slimCRT TV(21fu1r-ns of 220 voltage) in a recycling bin.

But,Unfortunately It is impossible to power on this slimCRT TV.

So I dismentled this slimCRT TV,and found that its fuse never have been blown and Voltage of big capacitor(main filter capacitor) is 315v

But I have little experience and knowledge about electronics repair,So I searched for any information about repairing "Not turning on CRT TV"

I found that it is necessary measuring voltage of drain and source pin in STR power regulator or measuring voltage of diode anode and cathode with power on.

But I really really dread that If I power on PCB of this slimCRT TV and If there is something wrong with measuring method of digital multimeter,It would cause burst of cathode-ray tube or catching fire or electric-shock accident..

So I want to measure any doubtful diode or power regulator or any IC with power off.

Is it really necessary to power on this slimCRT TV in order to diagnose failure IC of this slim CRT TV?
 

Martaine2005

May 12, 2015
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Don’t run before you can walk!.
CRTs are very dangerous in the wrong hands!.
 

Delta Prime

Jul 29, 2020
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So I want to measure any doubtful diode or power regulator or any IC with power off
You have to know how to solder and desolder the individual discrete components and check them out of circuit.
So I dismentled this slimCRT TV,and found that its fuse never have been blown and Voltage of big capacitor(main filter capacitor) is 315v
Capacitors can hold a very large charge over time. You must discharge these main filter capacitors using a power resistor with the value of 100 to 1000 ohms whose power dissipation is no less than 10 watts connecting the power resistor in parallel with the positive and negative terminals of the capacitor effectively shorting out the charge transforming the stored energy into heat through the power resistor before you even touch it with the soldering iron. I have made this procedure clear and if you cannot follow it that's okay it means you should not proceed simple as that. So if you're going to do it anyway do it like this cuz eventually you have to power it on.
1684430580872_1709792793598.png
I really really dread that If I power on PCB of this slimCRT TV and If there is something wrong with measuring method of digital multimeter,It would cause burst of cathode-ray tube or catching fire or electric-shock accident
You forgot implode the tube is a vacuum tube it won't explode it'll implode sucking you and everything else in the room inside of it,
You will be trapped inside the TV like a genie in a bottle! They won't tell you that anywhere online....
 
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bshi02

Mar 7, 2024
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I'd advise since you know zero, throw it back in the bin and automatically extend your expected life span up to 10x.
Don’t run before you can walk!.
CRTs are very dangerous in the wrong hands!.
Is it somewhat safe, if I desolder randomly transistor or power regulator and test it by multimeter or LCR-T4 and If I found failure IC then resolder it with new IC?

Although I have little experience and knowledge about electronics repair,I have experience microsoldering(successfully soldering jumping wire to broken mainboard trace which thickness is 0.06mm)
 

bshi02

Mar 7, 2024
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You have to know how to solder and desolder the individual discrete components and check them out of circuit.

Capacitors can hold a very large charge over time. You must discharge these main filter capacitors using a power resistor with the value of 100 to 1000 ohms whose power dissipation is no less than 10 watts connecting the power resistor in parallel with the positive and negative terminals of the capacitor effectively shorting out the charge transforming the stored energy into heat through the power resistor before you even touch it with the soldering iron. I have made this procedure clear and if you cannot follow it that's okay it means you should not proceed simple as that. So if you're going to do it anyway do it like this cuz eventually you have to power it on.
View attachment 63011

You forgot implode the tube is a vacuum tube it won't explode it'll implode sucking you and everything else in the room inside of it,
You will be trapped inside the TV like a genie in a bottle! They won't tell you that anywhere online....
Thank you very much for reply!
Infact I have two 2.5k ohm 5w ceramic resisitor,Is it dangerous to discharge this main filter capacitors by connecting either one of 2.5k ohm 5w ceramic resisitor with the positive and negative terminals of the capacitor?

and Is it safe to make use of DIm Bulb Tester of below link when I replaced doubtful or failure IC and have to test with power on slimCRT TV's PCB?
And Is It possible to use any watts of bulb for testing this PCB?
 

Delta Prime

Jul 29, 2020
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What about the genie in the bottle part didn't scare you one bit huh!
You did your homework.
You cannot use in any way shape or form that link you provided https://www.instructables.com/DIm-Bulb-Tester-Current-Limiter/

If you try that with you're CRT you will have a blob of burning plastic and it will catch fire I'm not trying to scare you when you deal with the AC never use anything soldered together they're all done with hardware with screws and wire nuts things of that nature and very thick heavy solid copper wire 10 gauge.
But forget about that for right now you're like 2 days away from assembling a current limiter.
I believe you're a competent and cautious most of all I'm going to tell you this and this is the truth. Have somebody there by your side observing who is older than you.. As for the capacitors.
Infact I have two 2.5k ohm 5w ceramic resisitor
Connect your power resistors in parallel twist the ends together. That'll be safer than just using one and you will safely quickly discharge that capacitor. Your digital multimeter if capable of measuring voltages over 350 volts DC measure the voltage across the capacitor only after you've shorted it with the power resistors tell me the results. Do not touch any of the traces on the bottom side where you're going to short the capacitor grab the board by the edges if you have rubber gloves wear them they could be the thin ones in .
 

Delta Prime

Jul 29, 2020
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Forgive me it is past my bedtime I have to go now. I know resources are limited they're limited everywhere just don't rush into anything if something happens to you I couldn't live with it.Because you would be dead. Good night.
One more thing, take photos please.
 
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Bluejets

Oct 5, 2014
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Thank you very much for reply!
Infact I have two 2.5k ohm 5w ceramic resisitor,Is it dangerous to discharge this main filter capacitors by connecting either one of 2.5k ohm 5w ceramic resisitor with the positive and negative terminals of the capacitor?

and Is it safe to make use of DIm Bulb Tester of below link when I replaced doubtful or failure IC and have to test with power on slimCRT TV's PCB?
And Is It possible to use any watts of bulb for testing this PCB?
Do you know how to discharge the crt tube????
I'll wager not....
 

bshi02

Mar 7, 2024
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Thank you very much for reply!
I took pictures of PCB of this slimCRT TV and upload it to imgbb site.


I found that The biggest capacitor(main filter capacitor) is 400wv 220uf samwha capacitor and Its voltage is 280v.
I assume that its voltage must be measured less than 10-20v, If bleeder resistor(there is 8w large ceramic resistor which is adjacent to main filer capacitor) correctly works.
But two days ago, Its voltage was 315v and Now It is 280v.
It means that there is only 35 voltage drop during two days...

And I found below link which inform me of the way how to calculate total energy stored in the capacitor.
So I calculated total watts using below formula.

1/2C⋅V^2=1/2*220*1/10^6*280^2=8.624Joules.

I conclude that It would be somewhat dangerous to discharge main filter capacitor with 5w ceramic resistor.
So I put off slimCRT TV's PCB examining until I purchase 10w ceramic resistor.

And As for discharging the crt tube, I always follow guide of below link(You can translate this guide(korean) to english by using Chrome or Edge's built-in translation)

 
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Delta Prime

Jul 29, 2020
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Don't think we'll be hearing from the blue origami airplane maker.
Well done... if you get stuck, come on back.
No need for translation. On the link you have provided. I speak and read 4 separate languages one day I will Master one of them. :):cool:
 
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Bluejets

Oct 5, 2014
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Think you'll find somewhere that this is an English based language only.

Irrelevant for me really as I already know how, point is, as I said, do you.
 

bshi02

Mar 7, 2024
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Don't think we'll be hearing from the blue origami airplane maker.
Well done... if you get stuck, come on back.
No need for translation. On the link you have provided. I speak and read 4 separate languages one day I will Master one of them. :):cool:
Thank very much for your reply!
Infact,There is no site or forum in my nation where I can learn how to repair electronics..
So,I have no choice but to throw out questions on this maker pro site.
I hope that I accustom myself to repair any electronics including CRT TV like you! :)
 

Delta Prime

Jul 29, 2020
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As a fellow member of this community I believe you can be a great assistance to another member who's planning on visiting your county.
Be warned I have made a comment about barbecue pork.I developed trichinosis and a bad bacterial infection but that was my fault I'm a total carnivore I asked them to lightly cook it (I did not include that part in my statement). The last time I visited your country . I found out you have excellent physicians.
You'll understand if you click here. Thank you.
 

bshi02

Mar 7, 2024
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I'm sorry that I delayed too long in replying, Frankly speaking a few weeks ago, I came across another CRT TV(anam ck-29p8lt) in a recycling bin,And When I have brought it to my house, I just found that Its ac power cord already have been cut by someone,So I replaced its broken AC power cord with AC power cord of slimCRT TV(21fu1r-ns of 220 voltage) which I have tried to fix,and It seems that this 29 inch CRT TV flawlessly works!
But I'm still interested in fixing this slimCRT TV(21fu1r-ns of 220 voltage).
So I made primitive and clumsy capacitor discharge tool which made use of 2kohm 10watts ceramic resistor, So I discharged the biggest capacitor with this clumsy discharge tools,But To my surprise, This biggest capacitor still had 260 voltage before I discharged it...anyway I finally successfully detached PCB of this slimCRT TV.

IMG_20240319_152718.jpg

IMG_20240321_094227.jpg

And I luckly found MC059C diagram of below screenshot which which seems to be the same with 21fu1r-ns excepting for part of ic501 and ic661,ic751 and ic701.

316c4d974b3efc45356747e16ba4d945.jpeg

I narrowly deslodered large heat sink of STR-W6754 regulator which is in the way for measuring carbon resistor in the HOT area(It was very hard to desolder this large heat sink with my soldering skill), Then I measured ohm value of all of carbon resistor in the HOT area(R801,R802,R820,R805,R804,R810,R812,R807,R805,R809).
and I desoldered some of resistor which seems to need precise measurement,It seems that all of carbon resistor in the HOT area have somewhat same ohm value with each resistor in MC059C diagram.
and I even desoldered DB801(TS4B05G rectifier diode) and test it with LCR t4 meter and Its voltage seems to be within tolerance

IMG_20240328_104949.jpg

IMG_20240328_105427.jpg
IMG_20240328_105510.jpg
IMG_20240328_105353.jpg

I cannot understand why most of stored voltage in the largest capacitor won't be discharged in circuit even after a few weeks.... In the last resort, I desoldered C802 capacitor(pcx2 335m mkp 0.22uf 275v film capacitor) and measure its capacitor with LCR t4 meter and DMM.
IMG_20240328_125522.jpg
It measured 148.9pf in LCR t4 meter and 150pf in DMM.
I think that it is out of tolerance for capacitance of 0.22uf 275v film capacitor,But I wonder whether it is really reliable method to identify defective 275v film capacitor by making use of capacitance measurement in LCR t4 or DMM...

And I always have to throughly look up in internet dictionary in order to write any english sentence.Of course It always take so long time..
But If you have any question about my nation, Feel free to make any question.(But I think that South korea has little attraction for overseas travel,because Now Its market price is extremely high and always witness overfull fly tipping which usually abandoned for months in the street,and frequently have to suffer from severe air pollution which caused by huge yellow dust from China.
 

Harald Kapp

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It measured 148.9pf in LCR t4 meter
The image shows 148.9 nF. That is 70 % of the rated value of 220 nF. Out of tolerance but most likely not an issue that leads to malfunction.
 

Delta Prime

Jul 29, 2020
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I cannot understand why most of stored voltage in the largest capacitor won't be discharged in circuit even after a few weeks
Capacitors and inductors store electrical energy capacitors in an electric field, inductors in a magnetic field.
Capacitors are capable of holding onto charges for long periods of time. Especially if their circuit does not contain a “bleeder” resistor that dissipates the electric charge when the device is powered off, even if the electrolytic capacitors were charged out of circuit and left alone, theoretically they can store that electrical charge forever but impurities in the dielectric material allows leakage current to eventually discharge the capacitor. Manufacturers typically specify a voltage rating for capacitors, which is the maximum voltage that is safe to put across the capacitor. Exceeding this can break down the dielectric material in the capacitor.
Korean:
커패시터 및 인덕터는 전기 에너지를 저장합니다. 커패시터 전기장에서는 인덕터, 자기장에서는 인덕터.
커패시터는 오랜 시간 동안 전하를 유지할 수 있습니다. 특히 회로에 장치의 전원이 꺼질 때 전하를 소산하는 "블리더" 저항기가 포함되어 있지 않은 경우 전해 커패시터가 회로에서 충전되어 그대로 방치되더라도 이론적으로는 해당 전하를 영구적으로 저장할 수 있지만 내부에는 불순물이 있습니다. 유전체 재료는 누설 전류가 결국 커패시터를 방전하도록 허용합니다. 제조업체는 일반적으로 커패시터의 최대 전압인 정격 전압을 지정합니다. 커패시터에 두는 것이 안전합니다. 이를 초과하면 유전체 재료가 파손될 수 있습니다. 콘덴서
 

bshi02

Mar 7, 2024
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Thank you very much for reply!
I read ebook which is called "CRT TV repair course" and It said


All Switch Mode Power Supply have start up resistor,If you follow these resistor they will got to the base of the switching transistor or control IC
when the smps uses IC the start up voltage goes to the Vcc pin of that IC, without this voltage smps cannot start,the supply will appear dead.
If there is a problem on the start up circuit the power supply just stop working,please note that these resistors also act as bleeder resistor for the main capacitor,when you find the main cap is still holding charge long after the set haves been disconnected from the supply,It maybe becasue start up resistor is opened or circuit board is cracked therefore there is no path to discharge the main capacitor.

After have reading this instructions,I concluded that there must have a problem with resistor which is located in HOT area.So I measured all of carbon resistors in HOT area.
 

bshi02

Mar 7, 2024
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After reading through chapter of "Solving power supply problems using control ic" in "CRT TV repair course" Ebook, I realized that In order to discharge main filter capacitor in CRT TV's circuit, Drain pin of power regulator must be connected to Vcc in pin of power regulator which lead to start up resistor(R812 100k ohm,R804 47k ohm,R805 47k ohm,R809 1k ohm).
So It is necessary to test power regulator(STR-W6754) with connecting all of connector and circuit to cathode-ray tubes and switching on power supply. But I still don't have any experience to test any power regulator.
So I'm afraid to test power regulator with switching on power supply.
Is there any method to test power regulator(STR-W6754) without switching on power supply?
 
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