lenovo smps repair , trouble identify the resistors - Page 1
Forum section: electronics / repair

author: BeetleJuice
author_rank: Contributor
timestamp: November 25, 2019, 12:45:14 pm
content: hi there ,i try to repair that smps , these two resistors (R10/R15) show 0.2ohms when desoldered from pbc.i try to decode the colors but i am confused ! that silver in the middle doesnt make sense at all..the smps had a mosfet burned , you see the x in the HS (IRF740).the other mosfet far left is K3934 and in the middle is a B129N diode.thank you for the help in advance!

author: BeetleJuice
author_rank: Contributor
timestamp: November 25, 2019, 01:29:54 pm
content: I believe its:brown black gray gold green = 10.8 ohm 0.5%black purple gray gold green = 7.8 ohm 0,5%can someone verify this? it looks more like silver band but probably its gray.

author: PKTKS
author_rank: Super Contributor
timestamp: November 25, 2019, 02:26:38 pm
content: Quote from: BeetleJuice on November 25, 2019, 01:29:54 pmThe first one should be OK - in doubt I would measure itThe second one makes no sense.Paul

author: wraper
author_rank: Unknown
timestamp: November 25, 2019, 02:36:17 pm
content: 0.1 OHm and 70 mOhm. These are not 5 band resistors. Green band should indicate resistor type, nothing to do with resistance. FYI resistors don't fail short.

author: PKTKS
author_rank: Super Contributor
timestamp: November 25, 2019, 02:45:44 pm
content: Quote from: wraper on November 25, 2019, 02:36:17 pmHmmm they look like old style classic wire wound typein something like a "new" 2Watt rating..Do you have some table for these color codes?Paul

author: wraper
author_rank: Unknown
timestamp: November 25, 2019, 03:12:44 pm
content: Quote from: PKTKS on November 25, 2019, 02:45:44 pmMost likely it's not power rating or any parameter. Say you can find in datasheet that this particular resistor series have green band. Consider this band non standard.

author: wraper
author_rank: Unknown
timestamp: November 25, 2019, 03:25:48 pm
content: Here is examplehttp://www.farnell.com/datasheets/87422.pdf.Quote

author: BeetleJuice
author_rank: Contributor
timestamp: November 25, 2019, 11:16:27 pm
content: Quote from: PKTKS on November 25, 2019, 02:45:44 pmomg how is this possible! since I don't have a milliohm meter I guess the 0,2 ohms i read with my multimeter shows that these resistors are ok.they drive the two mosfets I think, I am not sure I should make a schematic to see the wiring.i cant understand why these are not 5 band resistors, i mean what tells us that these are not? maybe the silver band that makes no sense?you must be right, cause its impossible to have 2 resistors short to 0,2ohms the same time, so the most logical explanation is that they are sub-ohm resistors so my multimeter and the resistor table i am looking is wrong.thank you for the reply!

author: BeetleJuice
author_rank: Contributor
timestamp: November 25, 2019, 11:21:15 pm
content: Quote from: wraper on November 25, 2019, 02:36:17 pmany idea what these resistors are doing with so small value?

author: wraper
author_rank: Unknown
timestamp: November 25, 2019, 11:28:10 pm
content: Quote from: BeetleJuice on November 25, 2019, 11:21:15 pmLikely current sense at MOSFET source.