resistor frequently blown

[Nigel Goodwin]

Tony Stewart when it is replaced it work for four to five days only. Afterward it burnt with smoke, display disappear and cannot start.

If the resistor is stopping it working, then it's NOT where you showed it on the rough circuit - as that's only a safety component and has no effect on it working.

 

[2PAC Mafia]

Hi,

If the resistor is stopping it working, then it's NOT where you showed it on the rough circuit - as that's only a safety component and has no effect on it working.

Althought I don´t think the resistor is connected to earth as it showed in the schematic, in case it is and the resistor goes in short then AC goes to earth so usually it should trip the earth leakage protection device at main electrical box, if you don´t have the earth derivation protection the chasis is with AC so you can get an electrical shock. In case the resistor is open then you don´t have that problem.

Tony Stewart when it is replaced it work for four to five days only. Afterward it burnt with smoke, display disappear and cannot start.

May be some component is out of range and if you can´t find it you can increase the wattage from the resistor and check if it works more days or also is damaged.

 

[ngzek]

Here I tried and reconstruct the damage circuit

 

[Nigel Goodwin]

Here I tried and reconstruct the damage circuit

Assuming the red line accurately shows a PCB track, then CY101/102 are safety capacitors, and the resistor is a high value safety resistor - just checked a few satellite receiver PSU's and they all use either 4.7M or 10M, with capacitors varying from 1nF to 4.7nF.

But this resistor won't stop it working, with it removed the unit will still be 100% functional, it only provided a high resistance static path back to the mains, and thus to earth.

If it doesn't work with the resistor removed (and it shouldn't be a low value anyway!) then you have a fault somewhere preventing it from working.

 

[ngzek]

Nigel Goodwin when it start burning sound got distorted, displaying white lines and colors become black and white like tv without signals. As you said above I need service manual and its components data which i have been looking for so long but cannot find till date. If cannot find I'll try with high value range(4.7M to 10M, with capacitors varying from 1nF to 4.7nF) suggested by you. Let me return to this page. Thank you Nigel Goodwin

 

[Nigel Goodwin]

Nigel Goodwin when it start burning sound got distorted, displaying white lines and colors become black and white like tv without signals. As you said above I need service manual and its components data which i have been looking for so long but cannot find till date. If cannot find I'll try with high value range(4.7M to 10M, with capacitors varying from 1nF to 4.7nF) suggested by you. Let me return to this page. Thank you Nigel Goodwin

It's unlikely the circuit is available, you're probably supposed to just replace the entire PCB - for the short time that replacements are available.

You don't need to fit a high value resistor, just leave it out (for fault finding purposes), and the two capacitors as well if you want - none of them affect the operation of the set in any way (they just provide a leakage path to earth for any static build-up on the chassis).

 

[Les Jones]

The service manual is available from here https://www.electronica-pt.com/esquema/func-startdown/14805/
but it does not contain the schematic of the power supply. It does say that the leakage to earth from the chassis should be less than 0.5 mA. (So the resistor that is burning out should be at least 500 K assuming 240 volt mains.) If the component CY101 which connects to the other leg of the mains (See picture in post #23) was short circuit or leaky it could explain why the resistor is burning out. (I think CY101 and CY102 could be spark gaps.) As others have said this failure should not stop the item from working. There must be another fault somewhere. The fact that this resistor is burning out is potentially dangerous as the antenna connector may be connected to the chassis. (It could also be isolated from the chassis with capacitors.) Due to the potential danger from the fault I think the OP should either get someone with more knowledge to look at the fault or replace the power supply board.

Les.

 

[Nigel Goodwin]

The service manual is available from here https://www.electronica-pt.com/esquema/func-startdown/14805/
but it does not contain the schematic of the power supply.

Like I said above, it's unlikely to be available - even on sets that give circuits the PSU (and also CCFL inverters) usually aren't given as they are commonly 'bought in' parts.

A useful technique in either of the cases is to google the IC's used, often the datasheet will include a sample circuit - which at least gives you a vague idea.

It does say that the leakage to earth from the chassis should be less than 0.5 mA. (So the resistor that is burning out should be at least 500 K assuming 240 volt mains.) If the component CY101 which connects to the other leg of the mains (See picture in post #23) was short circuit or leaky it could explain why the resistor is burning out. (I think CY101 and CY102 could be spark gaps.)

They are capacitors, although they 'may' have spark gaps built in the top of them (it's something you see occasionally - and also on tube bases).

As others have said this failure should not stop the item from working. There must be another fault somewhere. The fact that this resistor is burning out is potentially dangerous as the antenna connector may be connected to the chassis. (It could also be isolated from the chassis with capacitors.) Due to the potential danger from the fault I think the OP should either get someone with more knowledge to look at the fault or replace the power supply board.

It would be EXTREMELY, EXTREMELY rare to have a capacitor isolated aerial socket, I don't think any flat screen TV ever has?, and CRT's hadn't for MANY years before that. In general, if a TV has a SCART socket (or any other form of external socket other than the aerial) then it's almost certainly an isolated chassis set - there were an incredibly small number of exceptions, the only one that springs to mind is an Hitachi 20 inch one (it used opto-couplers to isolate the SCART socket).

I'm somewhat baffled how replacing this resistor with a low value one makes it work?, and how he came to discover this? - the original high value resistor wouldn't have burned up, so presumably it had already been replaced with an incorrect (and dangerous) low value before the OP got the set?.

 

[Tony Stewart]

If the resistor is burning up, that can mean several things.

1. The unit is drawing more current than it should for some reason, such as aging CCFL tubes which usually trigger shutdown of HVDC supply.
2. The resistor is too large a value and is overheating.
3. The resistor was replaced with an undersized for the nominal current and I^2R = Pd .

A PTC can be added in contact with the power resistor so that it can prevent over current and shutdown safely without burning out any parts, but will shutdown until cooled but the problem may be 1 above , so CCFL's need to be replaced with same.. Clues to aging are warm white in the corners or ends of the CCFL tubes.

Turn down the brightness may help.

**broken link removed**

 

[Nigel Goodwin]

If the resistor is burning up, that can mean several things.

1. The unit is drawing more current than it should for some reason, such as aging CCFL tubes which usually trigger shutdown of HVDC supply.
2. The resistor is too large a value and is overheating.
3. The resistor was replaced with an undersized for the nominal current and I^2R = Pd .

I suggest you try reading the previous posts, as not a single thing you posted here makes the slightest sense?.

 

[tunedwolf]

Yup, I agree with Nigel, those should simply be a static bleed resistor and low value caps. Looking at the first photo though, that blue "cap" thing looks a lot more like a varistor to me than a cap, which if that turned out to be the case, would be causing bad things to happen

 

[Tony Stewart]

Considering there is no power between Neutral and ground and maybe 0.5mA, a schematic error is the only thing that makes sense as suggested in #22

Pls explain how this burns up a resistor unless Line and Neutral are reversed,


EDIT

After reviewing photo.
It is clearly only for line filter caps & safety Y2 cap and bleeder R (10k)

Is reversed Line Neutral possible?

 

[Nigel Goodwin]

Considering there is no power between Neutral and ground and maybe 0.5mA, a schematic error is the only thing that makes sense as suggested in #22

Well you can usually draw considerably more between earth and neutral than 0.5mA, but it's only a small voltage.

Pls explain how this burns up a resistor unless Line and Neutral are reversed,

That wouldn't do it either, live and neutral are unlikely to be fixed, particularly in the USA with two pin plugs . Nor would totally removing the resistor and Y2 capacitor stop the unit working, as they are just safety components - to prevent static build-up.

Presumably there's a fault elsewhere?, and someone has somehow bodged things so badly that it's somehow passing current through this resistor, and they changed it for a massively lower value for that reason.

But I'm pretty bemused as to what you could do to cause that, and how someone could do something so badly wrong?.

 

[ngzek]

The service manual is available from here https://www.electronica-pt.com/esquema/func-startdown/14805/
but it does not contain the schematic of the power supply. It does say that the leakage to earth from the chassis should be less than 0.5 mA. (So the resistor that is burning out should be at least 500 K assuming 240 volt mains.) If the component CY101 which connects to the other leg of the mains (See picture in post #23) was short circuit or leaky it could explain why the resistor is burning out. (I think CY101 and CY102 could be spark gaps.) As others have said this failure should not stop the item from working. There must be another fault somewhere. The fact that this resistor is burning out is potentially dangerous as the antenna connector may be connected to the chassis. (It could also be isolated from the chassis with capacitors.) Due to the potential danger from the fault I think the OP should either get someone with more knowledge to look at the fault or replace the power supply board.

Les.

The service manual is available from here https://www.electronica-pt.com/esquema/func-startdown/14805/
but it does not contain the schematic of the power supply. It does say that the leakage to earth from the chassis should be less than 0.5 mA. (So the resistor that is burning out should be at least 500 K assuming 240 volt mains.) If the component CY101 which connects to the other leg of the mains (See picture in post #23) was short circuit or leaky it could explain why the resistor is burning out. (I think CY101 and CY102 could be spark gaps.) As others have said this failure should not stop the item from working. There must be another fault somewhere. The fact that this resistor is burning out is potentially dangerous as the antenna connector may be connected to the chassis. (It could also be isolated from the chassis with capacitors.) Due to the potential danger from the fault I think the OP should either get someone with more knowledge to look at the fault or replace the power supply board.

Les.

Thanks Les Jones for the service manual and your help. Now I can have the right value. Yes the main AC line volt is 133v and there is dangerous current with the antena

 

[ngzek]

If the resistor is burning up, that can mean several things.

1. The unit is drawing more current than it should for some reason, such as aging CCFL tubes which usually trigger shutdown of HVDC supply.
2. The resistor is too large a value and is overheating.
3. The resistor was replaced with an undersized for the nominal current and I^2R = Pd .

A PTC can be added in contact with the power resistor so that it can prevent over current and shutdown safely without burning out any parts, but will shutdown until cooled but the problem may be 1 above , so CCFL's need to be replaced with same.. Clues to aging are warm white in the corners or ends of the CCFL tubes.

Turn down the brightness may help.

**broken link removed**

This LCD tv is 4yrs old and its aging ccfl may be the cause. This reristor had blown thrice and I used to replace with 47ohms as suggested by local tech. Thanks for your informative help. I'll turn down and see

 

[Nigel Goodwin]

This LCD tv is 4yrs old and its aging ccfl may be the cause. This reristor had blown thrice and I used to replace with 47ohms as suggested by local tech. Thanks for your informative help. I'll turn down and see

None of what he posted was in any way relevant, as he was still assuming it was a surge limiter resistor - for that matter, ageing CCFL tubes wouldn't cause any such effect either.

 

[ngzek]

None of what he posted was in any way relevant, as he was still assuming it was a surge limiter resistor - for that matter, ageing CCFL tubes wouldn't cause any such effect either.

Nigel Goodwin according to your suggestion i fixed up without the resistor and the blue component, its working fine without any problem! but there is strong current with the antenna. should i replace with 500k ohm resistor?

 

[Tony Stewart]

I stand by my original comments. This is not a power resistor, but it will blow with a lot of power if Line and neutral are reverse wired in house. even if TV is correct with 3 pronged plug.

Well you can usually draw considerably more between earth and neutral than 0.5mA, but it's only a small voltage.

Not according to UL requirements. it is 3.5mA at 60Hz leakage to ground MAX per stationary unit.

That wouldn't do it either, live and neutral are unlikely to be fixed, particularly in the USA with two pin plugs .

They curbed using 2 pin plugs since VGA ports were added to TV's and monitors to reduce emissions.
This unit is 3 pin, unless a cheater cord was used.

Nor would totally removing the resistor and Y2 capacitor stop the unit working, as they are just safety components - to prevent static build-up.

It wasn't clear if the unit stopped working or it just started to fizzle. Nor was it clear what R values were originally there and replaced with same value and power rating and if in close proximity to a PTC which will regulate at 85'C during protection.


Burnt R can be 200K 1/4W

Presumably there's a fault elsewhere?, and someone has somehow bodged things so badly that it's somehow passing current through this resistor, and they changed it for a massively lower value for that reason.

As I indicated as CCFL's age they draw more power which would only affect series power drop Resistors.

But I'm pretty bemused as to what you could do to cause that, and how someone could do something so badly wrong?.

Putting 120V across a 10K R used to bleed a Y2 Cap would certainly do that and still work as a TV unit with SMPS isolation but noise interference. This could only happen if Line & Neutral were reversed unintentionally. ( DIY wiring by someone)

This is how I would show schematic. Feel free to correct any assumptions.

NOTE: CX101 means it is an X rated Cap line to line.
CY101 means it is a Y rated cap. Common mode to ground

Burnt R can be 200K 1/4W
Cap must be film Y rated for the Y rated position.

CY101 makes the antenna slightly hot ( < 3.5mA)
edit... ( but only if you got no safety ground and a miswired AC outlet. )

 

[ngzek]

Is my house line and neutral reverse? There is current in our metal body cooler and it stop when I break the ground pin and reverse the two pin connection.

 

[Tony Stewart]

Are you saying you don't know which pin is line or neutral and how the CM filter works or how to ensure a safety ground is on a metal container cooler?

yet you are trying to repair this?