Part identification. Odd value resistor in a dead SMPS? - Page 1
Forum section: electronics / repair

author: Robert A
author_rank: Contributor
timestamp: September 11, 2019, 10:31:12 am
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 11, 2019, 10:56:23 am
content: Please do NOT double post!

author: Robert A
author_rank: Contributor
timestamp: September 11, 2019, 11:10:36 am
content: Sorry. New to all this stuff. Have deleted other post. 🥺

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 11, 2019, 11:15:08 am
content: 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?

author: Robert A
author_rank: Contributor
timestamp: September 11, 2019, 11:23:55 am
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 11, 2019, 11:30:53 am
content: 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.

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: September 11, 2019, 05:18:38 pm
content: 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.

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 12, 2019, 01:33:35 am
content: 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, 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.jpghttps://ru.gecid.com/data/power/201712180800-50586/img/16_cooler_master_masterwatt_lite_700.jpg

author: Chris56000
author_rank: Frequent Contributor
timestamp: September 12, 2019, 11:47:11 am
content: 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

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 12, 2019, 04:38:36 pm
content: 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.