# HELP! Burnt Resistor For LED Smart Bulb

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#### Jujudragon

##### New Member
Hello! I am no pro at electronics but I know basic on soldering. Here is my problem. I have a burnt resistor. Looks like it has 5 bands but it's really hard to tell what colors they are. I'm just wondering what kind of resistor I need to order.

The smart bulb has a wireless card.

Thank for the help!!

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#### Nigel Goodwin

##### Super Moderator
Assuming it came out of the area marked F1/MOV1 then it's not a 'resistor', it's either some kind of fusible resistor or a MOV (varistor) - in either case it's difficult to know what 'value' it might be, and even if that is the only issue with the board. It's there as a safety device, and will blow if something serious goes wrong on the rest of the board, which would be more likely than it just randomly failing.

#### Jesse18

##### New Member
Use a multimeter in mA mode to take the place of the fuse. power up the unit with the lights plugged in. The multimeter will tell you the mA used by the driver board. Then find a fuse that is rated 30% higher than the readout on the multimeter.

#### Nigel Goodwin

##### Super Moderator
Use a multimeter in mA mode to take the place of the fuse. power up the unit with the lights plugged in. The multimeter will tell you the mA used by the driver board. Then find a fuse that is rated 30% higher than the readout on the multimeter.

If this before or after you've picked the smoking ruins of your meter from where it's splattered round the room?.

You don't randonly connect your meter to the mains set to mA in the blind hope that there's not an actual fault - the most likely reason for failure of that component is something else far more serious having failed, which will destroy your meter by doing what you suggest (just the meter fuse if you're lucky).

#### Jujudragon

##### New Member
Assuming it came out of the area marked F1/MOV1 then it's not a 'resistor', it's either some kind of fusible resistor or a MOV (varistor) - in either case it's difficult to know what 'value' it might be, and even if that is the only issue with the board. It's there as a safety device, and will blow if something serious goes wrong on the rest of the board, which would be more likely than it just randomly failing.
Hi Nigel. Thanks for the response. Well I guess I would have to buy a new bulb? I already own another 5 of the same make and brand. I was going to buy a 'resistor' pack just in case any other bulbs fail. I could replace the part and have it on a separate safe outlet just to test it. And yes, it came from the F1. the MOV1 varistor is still there and it's blue and it's not burnt.

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#### Jujudragon

##### New Member
Use a multimeter in mA mode to take the place of the fuse. power up the unit with the lights plugged in. The multimeter will tell you the mA used by the driver board. Then find a fuse that is rated 30% higher than the readout on the multimeter.
Hey thanks for the response. Would one of these do the job?

Thanks again!

#### Les Jones

##### Well-Known Member
DO NOT TRY the suggestion in post #3 of using a multimeter as a very expensive fuse. I you want to see if there is another fault on the board (Which I am almost certain there will be.) that caused the original fusible resistor to fail the try connecting an old fashioned filament lamp (Not a halogen bulb.) with a voltage rating equal to the mains voltage in your country and a wattage rating of about 20 to 40 watts. in place of the fusible resistor. If it lights at full brightness then there is a major fault on the board.

Les.

#### Jesse18

##### New Member
DO NOT TRY the suggestion in post #3 of using a multimeter as a very expensive fuse. I you want to see if there is another fault on the board (Which I am almost certain there will be.) that caused the original fusible resistor to fail the try connecting an old fashioned filament lamp (Not a halogen bulb.) with a voltage rating equal to the mains voltage in your country and a wattage rating of about 20 to 40 watts. in place of the fusible resistor. If it lights at full brightness then there is a major fault on the board.

Les.

He posted an $11 multimeter with a 10cent fuse in it. Not a big deal. Not everyone runs around with a$500 Fluke on their bench.

#### Nigel Goodwin

##### Super Moderator
He posted an $11 multimeter with a 10cent fuse in it. Not a big deal. Not everyone runs around with a$500 Fluke on their bench.

So?, it's still a silly think to do, regardless of the cost of what you're destroying - and the cost of a meter is relative to what you can afford.

#### Jesse18

##### New Member
I disagree, I don't think it is a silly thing to do at all. I will grant your point about a short. He will still need to perform this procedure in order to determine the fuse that he needs to buy for the replacement. How do you think he can determine the fuse rating? The schematics for that PCB is more than likely not available. The cheapest wall socket amp meter on Amazon is \$16 and is probably not very accurate.

#### Jesse18

##### New Member
In fact, I would argue this procedure is exactly what the multimeter ampmeter function is designed to do, testing current in a live circuit.

#### Nigel Goodwin

##### Super Moderator
In fact, I would argue this procedure is exactly what the multimeter ampmeter function is designed to do, testing current in a live circuit.

You appear to be ignoring the entire point - which is that the bulb is almost certainly faulty, and short circuit - hence blowing what it did.

That is why everyone, except you, considers it a VERY bad idea to connect a meter in that way - without first ensuring the bulb is indeed NOT faulty. Once that is dpne, there's no isuue whatsoever about measuring the current - if you wanted to?.

Measuring the current only gives an extremely vague idea what size of fuse might be required, fuse sizing is an extremely complicated procedure, and is partly governed by surge requirements.

No reason to measure it anyway, it's a bulb - you already know it's wattage rating, which is more than accurate enough to give a clue as to what fuse you might like to 'try'.

Les Jones suggestion of using a 60W bulb as a current limiter is a good one, and standard procedure in service departments for many faults. Assuming you can still get a60W bulb of course?.

#### Jesse18

##### New Member
You are making an assumption that there is a short in the board, in that case he should just toss the thing in the garbage. I don't think there is a short (my assumption) because I have replaced a number of these types of fuses in the past on everything from wire feed welders to CD players. This type of fuse is a slow blow fuse that wears out over time. It is not a quick blow fuse like a typical glass fuse.

Again, telling him to use a bulb for testing is fine but that doesn't tell him what type or rating of fuse to use. I have a wide range of those fuses in my parts bins and would gladly send them to him.

I am not here to argue, I am here to help answer his question.

#### Nigel Goodwin

##### Super Moderator
You are making an assumption that there is a short in the board, in that case he should just toss the thing in the garbage. I don't think there is a short (my assumption) because I have replaced a number of these types of fuses in the past on everything from wire feed welders to CD players. This type of fuse is a slow blow fuse that wears out over time. It is not a quick blow fuse like a typical glass fuse.

In almost 50 years professional experience I've found that most glass fuses are anti-surge, and in fact we stocked else but antisurge fuses, with the exception of a few 'special' fuses for specific applications. Plug fuses (all UK plugs are fused) are fast blow, but are ceramic rather than glass.

I'm also not 'assuming' the board is short, I'm saying it's a good possibility - and it's utter stupidity to destroy a meter for no valid reason whatsoever. If you want to measure the current (and there seems no reason to?), then make sure the lamp works first - don't just stick the meter in circuit and see if it goes BANG.

Again, telling him to use a bulb for testing is fine but that doesn't tell him what type or rating of fuse to use. I have a wide range of those fuses in my parts bins and would gladly send them to him.

It really doesn't make that much difference, and the minimum rating is easily calculated from the wattage of the bulb - no need to measure the current at all.

#### Shoa

##### New Member
Take one of the other bulbs apart if they are the same, see if you can see the colours properly, you can test the other parts for reference to see whats shorted in the one that might have a short.

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