Author Topic: Part identification. Odd value resistor in a dead SMPS?  (Read 503 times)

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Offline Robert A

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Part identification. Odd value resistor in a dead SMPS?
« on: September 11, 2019, 10:31:12 am »
Hi, I need help identifying this resistor. It’s in an SMPS and has let the magic smoke out. The bands look like they are black, white, silver, gold and green but that doesn’t calculate to anything sensible. Also I think it’s in a 1W case. Any help is appreciated.
 

Online PA0PBZ

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #1 on: September 11, 2019, 10:56:23 am »
Please do NOT double post!
Keyboard error: Press F1 to continue.
 

Offline Robert A

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #2 on: September 11, 2019, 11:10:36 am »
Sorry. New to all this stuff. Have deleted other post. 🥺
 

Offline MagicSmoker

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #3 on: September 11, 2019, 11:15:08 am »
You're right - the color code doesn't make sense. So how about posting a picture showing more of the surrounding area and/or any of the circuit you might have reverse-engineered so far from following traces and components?

 

Offline Robert A

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #4 on: September 11, 2019, 11:23:55 am »
This is the only other photo I’ve got at the moment but I haven’t started to reverse engineer yet. If it’s any help it a Coolmaster 700W PC power supply, model number mpx-7001-acabw.
 

Online PA0PBZ

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #5 on: September 11, 2019, 11:30:53 am »
Since neither silver or gold are valid value bands I can only assume that silver is the multiplier and gold the tolerance, giving 0.09 Ohm 5%.
The green band could indicate that it is a safety resistor or it has a 20ppm/K tempco.
« Last Edit: September 11, 2019, 11:35:26 am by PA0PBZ »
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Online 4thDoctorWhoFan

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #6 on: September 11, 2019, 05:18:38 pm »
Since silver is not a normal third band on a 5 band resistor, perhaps instead of silver, it's gray.  If it has smoked, the coloring could be off also.
Assuming it's gray instead of silver, that would make it a 9.8 ohm 1% resistor.
 

Offline shakalnokturn

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #7 on: September 12, 2019, 01:33:35 am »
Inrush current limiting (although there is also a NTC).
Even with other photos I can't make sense of the colour code.
Going by the PSU rated output power something in the 5-10 \$\Omega\$, 2-3W range should be reasonable.
Has the PFC stage shorted?

https://ru.gecid.com/data/power/201712180800-50586/img/21_cooler_master_masterwatt_lite_700.jpg

https://ru.gecid.com/data/power/201712180800-50586/img/16_cooler_master_masterwatt_lite_700.jpg

 

Offline Chris56000

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #8 on: September 12, 2019, 11:47:11 am »
Hi!

It's quite common for brown bands on power-oxide resistors to dis-colour to black and light colours dis-colour to white when overheated, so looking at it, me thinks it's coded 0.18 Ω @ 2W rating, so begin with a 0.18 Ω 2W from RS, Farnell or Mouser - from the rating of the power supply you've given, that looks like a reasonable choice to begin with!

I'd order two or three in case you've got another primary-side or PFC fault that you don't catch first go, than you've got one or two spare!

Chris Williams

« Last Edit: September 12, 2019, 11:52:02 am by Chris56000 »
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 

Offline shakalnokturn

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Re: Part identification. Odd value resistor in a dead SMPS?
« Reply #9 on: September 12, 2019, 04:38:36 pm »
Having a second look at the layout it does look like it could be PFC current sense rather than inrush limit, so the above suggestion is much wiser than mine was.
 


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