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    My CRT TV IS TOTALY DEAD, THE fuse is blown

    Dear Friends,

    Good Morning, My CRT TV is fully dead, I checked the fuse is burned, I checked the two diode using multimeter, from after removing the motherboard, that is shorted (I got beep sound, other two is not shorted), I checked the power capacitor there is no any voltage, now what to do ? How to check the power IC ? how to check other components ? please help me in this case ........

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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    With a CRT, there there are two high power units, one is the line output from which the EHT is derived (say 50W) and the frame output (say 20 W). Normally the line output stage is fed by at least 100V. So your incoming mains could be rectified to produce 200V and a transformer used to get 12V for the small signal stages. Or the mains could be rectified and used to power a switch mode power supply which has a transformer and diode bridges to supply all the various voltages. This is the most likely. So you must identify what sort of power supply is fitted.
    Frank



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    I found there two diode was shorted and fuse was burnt, there is no any other burnt components... if i change all diodes and EHT (power IC D5038) then I'll check with series bulb in fuse place.... Is there any other way to get ON my CRT TV ? please help me, and i have schematic diagram, Mr brian Sir was given me last time.....



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Dear Electronic Experts, I change the power IC , DIODES, CAPACITOR and a transistor but still the bulb is bright, What to do? please help me.....



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    It could be many things, including that it may not be able to start up with the bulb instead of a fuse. Which TV is this, the same one as in your other thread?
    Please tell us the model number again.

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    When an old CRT TV dies today most people throw it away and buy a wide screen LCD TV.
    But I still use two CRT TVs that are not even high definition.

    They are selling 4k Ultra High Definition TVs now. I do not know any local stations that transmit it. Maybe a movie on a DVD might be in 4k Ultra HD. My cable TV provider has 4k Ultra HD now.



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Dear Brian Sir,
    Thanks for your help, Your given me LA76931S 58Y4 schematic diagram, I was changed Power IC, Power capacitor, Posistor and 4 diodes. I connect an series bulb in fuse place, but still the bulb is bright...



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Connecting a light bulb instead of the fuse will not help. The CRT has a deguassing circuit that requires high power for a few seconds before it goes to standby. By wiring a light bulb you are limiting the current it can draw and keeping it in high power state.

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    A bulb is a PTC device like Polyfuse (PTC) but may be not enough current to charge up Caps and degauss coil.

    Use a bigger/more bulbs instead or get proper rated Polyfuse and disconnect circuits that load main supply until stable. Then check main power DC sources after reconnect and turn on.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Click image for larger version. 

Name:	LA76931 schematic diagram-page-001.jpg 
Views:	14 
Size:	466.8 KB 
ID:	123434 , Thanks Brian and Sunny Sir, Then how to connect the bulb? Where to connect? Still I am not installed fuse and I am not getting standby also, Please help me...... (I have attached schematic diagram, Mr Brian Sir Given me last time, the same TV) .



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    A bulb is not part of a TV technicians repair kit! You cannot use it instead of a fuse. I'm not sure why you are using one but wherever you connect it is wrong!

    Lets go back to basics:
    There is no 'power IC' so what was it you changed?
    Which two diodes were shorted?
    Which capacitor are you saying "has no voltage across it"?
    I can't see a "D5038" on the schematic, where is it?

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Dear Brian Sir,
    You gave me the model schematic, but it's not same like my TV, But it was very useful for me. I changed the Power D5038 Transistor, Transistor C3807 and posistor, I have attached the images, will you please help to get ON my crt TV again..... please.......... help me Sir, Thanks in advance . (Click image for larger version. 

Name:	1n4007_1_.jpg 
Views:	2 
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ID:	123467Click image for larger version. 

Name:	capacitor discharge.jpg 
Views:	3 
Size:	36.4 KB 
ID:	123468Click image for larger version. 

Name:	d5038.jpg 
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ID:	123469Click image for larger version. 

Name:	posistor_69-2.jpg 
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ID:	123470Click image for larger version. 

Name:	5pcs-Low-Frequency-AMP-Transistor-NPN-2SC3807-C3807-NEW.jpg 
Views:	2 
Size:	40.8 KB 
ID:	123471

    - - - Updated - - -

    Dear Brian SIr,
    I have only basic knowledge in electronics, I don't know much about electronis. I would like to learn electronics but there is no way, But I would like to learn electronics from websites like edaboard and etc., at least I would like to learn our home product repair, like TV, DVD player, Mixer Grinder, Grinder, CFL and more..... This is my hobby, but I was studied electrical only, not electronics, But I love electronics ...... That why I am asking some doubt's in this forum. Thanks for this website and friends....
    Last edited by SHIVAKUMAR K; 25th November 2015 at 07:42.



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    I have boxes of those components here so photographs of them don't help!

    What I need is an accurate schematic so I can suggest places to measure voltages. Every TV model is different but most use the same R,C, L, TR... prefixes so the references for one model could be to something completely different in another model.

    Please tell me the exact manufacturer and model number from the label on the rear of the TV so I can trace the correct diagram (if that's possible).

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Thanks Brian Sir,
    This is china Model,
    " CTV - 14" -KSA
    SERVICE DATA SANYO UOC MONO WITH FS TUNER SOUND O/P: 6.5W RMS
    BRAND: BPL
    SYSTEM IC - LA76931S-7N 58Y4
    CRT - SAMTEL- A34LEX10X, & DY - V TYPE "

    Like this written on the TV,



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    We have 4k Ultra High Definition TVs available now. Of course they use an LCD display, not a CRT. Some are very thin and I saw one with a curved screen that partially wraps around you.



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    I've searched but can't find a schematic fitting that description I'm afraid.

    Try looking on the circuit board for a part number, it may be surrounded by a box or something distinctive so it isn't confused with component references. There is a good chance the number will be on both sides of the board, possibly written in copper (like circuit tracks) on the bottom side.

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Ok Brian SIr,

    I'll will give you that NUMBER, How to check the power supply ? how to check diodes, resistor, capacitor and transistor in circuit board ? what I need to check that items good or not (i don't have oscilloscope please) how to repair SMPS ?



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    I'm lost as to where this thread is at but I'll give my analysis. My experience with a 4 diode bridge rectifier is generally two diodes short, fuse blows but other components ok. Changing all 4 diodes is the best fix. If the SMPS output also shorted then likely a ground fault occurred which cause large current from hot ground (power supply primary side) to cold ground (neutral). Components fail in shortest path to hot ground which is thru the diode rectifers, obviously thru the 2SD3058 and I'm assuming 2SC3807 is the driver connected to 2SD3058? You will need to use ohmmeter to check for low ohms (typically < 500 ohms) short between all leads of each diode, transistor. If low ohms then desolder to confirm short is in component. Unplug the degauss coil to eliminate surge then use a fast acting fuse, go by operating wattage rating on TV label divided by 120 (or 240) unless amperage is given. Do not over rate the fuse amperage. Have plenty of fuses

    PS - you can also diagnose by watching the fuse when you power on. If it bends or glows then opens then it's slight over current or under rated fuse. If it flashes bright instantaneously then there is a hard short circuit.

    Larry G
    Last edited by retrogear; 30th November 2015 at 19:08.



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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Half the problem we have had Larry is working from the wrong schematic! The one I assumed to be correct doesn't have the same part number as SHIVAKUMAR K has replaced so some of my advice may have been misleading. The TV he has is from an obscure Chinese manufacturer but may be re-badged in a more recognizable name if we can find one.

    There is also the rather worry aspect of "how to check diodes, resistor, capacitor and transistor in circuit board" while dealing with SMPS. Far from it being my wish to be obstructive but based on your previous posts I would guess that like me, you have a heathy respect for SMPS, and would agree they are not for the inexperienced to repair.

    The light bulb instead of as fuse is a bad idea, I would expect it to light on most CRT televisions while holding the degauss circuit active and possibly burning it out - without power even reaching the rectifiers. Randomly changing parts is equally unlikely to fix the fault or learn why the fault occurred in the first place. I'm concerned that replacing two diodes which seem from the description to be in a bridge configuration (but without a schematic they could be something else) and still not seeing any voltage at what is assumed to be the reservoir capacitor could mean an open circuit thermistor or a broken PCB track or even a faulty EMC filter. We really need more information to give a reliable diagnosis. Fixing TVs in front of you on the workbench can be hard enough sometimes, telling someone half way around the World what to do is near impossible - but we will keep trying!

    Brian.
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    Re: My CRT TV IS TOTALY DEAD, THE fuse is blown

    Yea I realized the schematic didn't match the part# 's he displayed. I think we have a language barrier also. SMPS are difficult to service and not just a matter of
    replacing a few obvious shorted parts and applying full power. Years ago I had factory training on specific models which gave a procedure to bring up on a variac to a specific AC level and check for certain waveforms before bringing up to full power. I remember one waveform in particular was the base of the output transistor should have a certain length of on-time but again, that was specific to that particular design. Without a matching schematic, it's going to be tough.

    Larry G



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