How to choose replacement resistors

[ChrisV]

Hey guys. I've recently purchased a replacement Y-Main board for a Vizio VP50 HDTV10A. This is the 2nd Vizio that I've been able to repair by repairing the power supply and then replacing the Y-Main and buffer boards. Although it felt good to see the TV's up and running, it would be much more fulfilling to repair the broken Y-Main. I've carefully inspected the board and found 2 burnt resistors. After checking all of the other resistors, there were several others that were out of the tolerance. In fact, only 2 of them on the board were good. I spent some time researching and understanding the color coding system and was able to determine that the 2 resistors in the photo are a 10ohm resistor.
What I don't understand is how to determine the correct wattage. I made a trip to Radio Shack and they had some 1/4W 10 Ohm resistors but they were physically smaller in size. I have a few different resistors and don't want to buy the wrong ones.
Any advice for a NOOB?

[Ltank]

Re: How to choose replacement resistors

Red Black Black is 20 Ohms Gold for 5%. Appears to be Flame proof 2 watt resistors,
hard to tell phsical size to be more accurate

[tom66]

Re: How to choose replacement resistors

Usually those resistors fail if there is a short on the buffer board.

[LLLlllou]

Re: How to choose replacement resistors

Red Black Black is 20 Ohms Gold for 5%. Appears to be Flame proof 2 watt resistors,
hard to tell phsical size to be more accurate

Definitely 20ohm 5%, looks flameproof, impossible to tell wattage with so little to go by, but definitely way over 1/4 watt.

OP, how'd ya get 10ohms out of red black black gold?

First and second color:
Black=0
Brown=1
Red=2
Orange=3
Yellow=4
Green=5
Blue=6
Violet=7
Grey=8
White=9

Third color (multiplier):
Silver=.01
Gold=x.1
Black=x1
Brown=x10
Red=x100
Orange=x1000
Yellow=x10000
Green=x100000
Blue=x1M

Fourth color (tolerance):
none=20%
Silver=10%
Gold=5%

(Red=2 Black=0) = 20 x Black=x1 = 20 ohms

[budm]

Re: How to choose replacement resistors

It looks like they are connected in parallel, the top ends of both resistors are connected to the large copper plain, the bottom end of both resistors has copper trace connected to the both resistors. One looks damaged. You should lift one end up and take the measurement.

[ChrisV]

Re: How to choose replacement resistors

Definitely 20ohm 5%, looks flameproof, impossible to tell wattage with so little to go by, but definitely way over 1/4 watt.

OP, how'd ya get 10ohms out of red black black gold?

First and second color:
Black=0
Brown=1
Red=2
Orange=3
Yellow=4
Green=5
Blue=6
Violet=7
Grey=8
White=9

Third color (multiplier):
Silver=.01
Gold=x.1
Black=x1
Brown=x10
Red=x100
Orange=x1000
Yellow=x10000
Green=x100000
Blue=x1M

Fourth color (tolerance):
none=20%
Silver=10%
Gold=5%

(Red=2 Black=0) = 20 x Black=x1 = 20 ohms

I guess that picture is a little deceiving. The colors are Brown black black gold.
The brown color on the first band would indicate a 1 for the first digit. I've attached a better photo. The resistor is about 12mm long

[ChrisV]

Re: How to choose replacement resistors

It looks like they are connected in parallel, the top ends of both resistors are connected to the large copper plain, the bottom end of both resistors has copper trace connected to the both resistors. One looks damaged. You should lift one end up and take the measurement.

Yes. They are in parallel. I've removed them from the circuit to measure them. My main concern is understanding how to order resistors after I've determined the resistance value. Just not sure about everything else. I have a few more resistors to replace and want to get it right on the first order.
Thank you for the reply!

[ChrisV]

Re: How to choose replacement resistors

Red Black Black is 20 Ohms Gold for 5%. Appears to be Flame proof 2 watt resistors,
hard to tell phsical size to be more accurate

Thank you for the reply. How can you see that they are 2 watt flame proof?

[ChrisV]

Re: How to choose replacement resistors

Usually those resistors fail if there is a short on the buffer board.

Both buffer boards were shorted out. Trying to determine the cause of failure.....
There were 10 blown capacitors on the power supply of this TV. Do you think the failed power supply caused erratic voltage to the Y-Main, which caused the buffer boards to short out? The shorted out buffer boards ultimately fried the resistors on the Y-Main???

[Alastair E]

Re: How to choose replacement resistors

Physical size and that matte green colour indicates wattage and flame-proof types. One pictured would be a 2W Metal-Film Flameproof, 10 ohm, 5% tolerance.

They are probably there--designed to fail-- in the event of a circuit failure elsewhere to protect against possible fire and other damage, basically doubling as a fuse--Such resistors are often marked on schematics with a 'Hazard' symbol, a ! in a triangle....

Often, they are used in the source connection of MOSFETS for current-monitoring in PSU's etc, so should always be replaced with exactly the same value--and type!

[ChrisV]

Re: How to choose replacement resistors

Thank you for the answers. That tells me everything I need to know to replace these.

[ChrisV]

Re: How to choose replacement resistors

Sorry. I thought I had this figured out. I'm checking all of the resistors on this board. This one has me stumped. It's a 5 band resistor. The #3 gold band in the resistor is confusing me. Any thoughts on the ohm rating?

[goontron]

Re: How to choose replacement resistors

i think that's an inductior, not a resistor

[budm]

Re: How to choose replacement resistors

I say 1 Ohm flame proof MOX resistor. Just measure it.

[selldoor]

Re: How to choose replacement resistors

Why dont you just test it and see what your meter comes up with?

EDIT
I agree with budm

see here test for 5 reports as 4 =1 ohm

http://www.hobby-hour.com/electronic...calculator.php

[goontron]

Re: How to choose replacement resistors

I say 1 Ohm flame proof MOX resistor. Just measure it.

if it is its only 2% tolerance, which seems odd for a telly.

[ChrisV]

Re: How to choose replacement resistors

It measures @ 1.2ohms. According to chart, the tolerance is 2%. So the upper limit would be 1.05 ohms. Is that correct. This is outside of the tolerance and should be replaced?

Thank you guys so much for the replies.

[goontron]

Re: How to choose replacement resistors

i would say its ok.

[budm]

Re: How to choose replacement resistors

That is probably sensing current resistor connected to the Source pin of the MOSFET so they use 2% instead of 5% for more accurate current sensing.
You have to add your meter probe wires resistance to the value of the resistor you are measuring.

[LLLlllou]

Re: How to choose replacement resistors

I guess that picture is a little deceiving. The colors are Brown black black gold.
The brown color on the first band would indicate a 1 for the first digit. I've attached a better photo. The resistor is about 12mm long

"A picture is worth a thousand words" - my ASS!

First pictures you posted show the first band as RED, second pic is definitely brown. Just goes to show, you can't believe every thing you see. :0

As Dennis Rodman once said to Carmen Electra after her finding him in bed with another woman - "are you gonna believe me, or you're lying eyes?"