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Help identifying a burnt resistor WB27X10438

  1. Jul 2, 2014 #1
    Hi guys,

    I was wondering if you could take a look at a resistor that burnt from my microwave pcb. I've had good luck in the past with replacing capacitors and other failed components but I am having a hard time seeing the colors of the resister.

    http://postimg.org/gallery/38ombk4a/
    [/URL]

    The board part number is WB27X10438 when I googled the part number I am able to see other boards on ebay with the same burn spot where the resistor burned on my board.

    The microwave was a ge spacemaker xl1800. Let me know if you need any other information that could help.

    Here's the ebay link looks like the same spot.

    http://www.ebay.com/itm/GE-General-Electric-Microwave-Oven-Circuit-Board-WB27X10438-/321444863512?pt=LH_DefaultDomain_0&hash=item4ad79b5e18

    Here's a link of someone selling a remanufactured board.

    http://www.ebay.com/itm/GE-Maytag-Whirlpool-Microwave-WB27X10438-/171320917216?pt=LH_DefaultDomain_0&hash=item27e385bce0

    There is one on amazon that looks like it might be dark in the same spots as well.

    https://www.amazon.com/Part-Number-WB27X10438-PCB-ASSY/dp/B001E0G6QM
    [/URL]

    I really appreciate any help you guys can provide.

    Thanks,
    Jason
     
    Last edited by a moderator: May 6, 2017
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  3. Jul 2, 2014 #2

    jim hardy

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  4. Jul 2, 2014 #3
    Hi Jim,

    Thanks for the reply I am going to look over the websites you've linked I've already been on digikey but I am having a tough time identifying the color bands. It's 5 bands but how do you know what side to start from?

    Thanks again,
    Jason
     
  5. Jul 2, 2014 #4

    jim hardy

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    I have that same problem,, which end is which.
    You have to treat it like a multiple choice question....
    Usually one direction deciphers to a non standard value or something like an impossible multiplier stripe that lets you rule it out.

    That last site, digikey's stripe decoder, will decode stripes that would represent nonstandard values , so you have to cross check what it gives you against the standard values from the middle link.


    Good luck !
     
  6. Jul 2, 2014 #5

    AlephZero

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  7. Jul 2, 2014 #6

    davenn

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    considering that the resistor doesn't look overly damaged ( yes it has got hot, but it may not have failed yet)
    why do you think it's faulty ?

    have you actually tested the resistor with a multimeter using the resistance ranges ?
    if so, what did it test ?

    You would be surprised how cooked looking they can get but still read their correct value

    cheers
    Dave
     
  8. Jul 3, 2014 #7
    Here is the info that ge has on my model - http://genet.geappliances.com/search/search?site=gea-litlib_collection&ou=utf-8&tlen=150&client=gea-litlib_frontend&output=xml_no_dtd&proxystylesheet=gea-litlib_frontend&filter=0&getfields=*&q=jvm1860sd&actualquerystring=jvm1860sd001 [Broken]

    Hi Dave I have to get the multimeter from my shop and I'll report back. You might be right it might still work what had happened was I started smelling smoke so I immediately turned it off. When I first took it apart I didn't see the burn mark on the board (I think I just over looked it) so I thought maybe the smell was from the metal shelf possibly touching the side and when I ran the microwave again everything seemed to work fine but I wasn't satisfied with my my shelf theory so I took everything apart again and sure enough I saw the burn mark this time. So maybe it would still be functional I will know more after I get my meter.

    Thanks guys! I'll be reporting back shortly!
     
    Last edited by a moderator: May 6, 2017
  9. Jul 3, 2014 #8

    davenn

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    if you are going to do electronics of any sort on a regular basis, a multimeter should be at the top of your tool list. Its almost impossible to do proper diagnostics without one.

    If the resistor has failed, and by the sounds of it its a common thing for it to get quite hot on this particular board
    The you need to consider why its getting hot and burning out.
    The most obvious/logical reason is that this is just a symptom of a fault further "down the line". Some other component has/is failed/failing and the excessive current through this resistor causing it to cook..

    This may well be a safety feature .... that is ... its better to sacrifice a 10c value resistor than to risk major component failure or risk the appliance bursting into flames under fault conditions


    cheers
    Dave
     
  10. Jul 3, 2014 #9
    I totally agree I actually have over 10 multimeters at home but they're the free harbor freight brand ones they give out for free and would not give me a reading.

    I got my Klein from the shop and when I set it to auto it gives me a reading of 30.10k - 30.12k ohm

    I get what your saying something maybe causing the resistor to fail.... Since this is the first problem I've had and it has worked fine for over 10 years do you think it's crazy to just try replacing the resistor and watch it carefully?

    Thanks,
    Jason
     
  11. Jul 3, 2014 #10

    davenn

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    30k isn't a standard value, BUT it would fall within the range of a 33k resistor with 5 or 10% tolerance

    the visible colour bands don't give an indication of that value, but because of the mix of overheating and photography light its difficult to determine the value visually

    33k Ohms = orange, orange, orange

    It would be worth trying a 33k at 1/2W rating and carefully observe what happens
    switch off as soon as some discolouration starts

    the other thing you could try and do to help us it trace some of the circuit out that leads to and away from that resistor.... maybe give us an idea of what other components the resistor is connected to


    cheers
    Dave
     
  12. Jul 3, 2014 #11

    jim hardy

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    You posted this photo
    http://postimg.org/image/3w3v1njmh/
    which could pass for left to right,
    brown violet grey silver red = 1.78 ohms 2%, which is a standard value


    or could pass for right to left
    red grey white red brown = 28.9k 1%
    which i dismissed as nonstandard value until you reported measuring 30.1k , only about 4% different.

    maybe you can make out the colors better in daylight with a loupe ?
    By the time i see them they've been through your camera and my screen and my old eyes.

    And here's a better stripe decoder that tells you whether a value is standard. I bookmarked it as "a handy reference to know about".
    http://www.searchingtabs.com/rcolor/deccolor.htm

    Dave's advice to look a little ways into the circuit is good. Knowing what it does would help make a SWAG as to likely resistance value. Or even whether it could be an inductor...

    Can you tell from the circuit board traces what its ends are connected to?

    Sometimes a low ohm metal film resistor is used for a fuse . That's to prevent somebody from replacing it with a bigger fuse instead of finding the trouble. Look for bulged electrolytic capacitors nearby.
     
  13. Jul 10, 2014 #12
    Hope everyone had a happy 4th!

    I had some time to play around with the resister when I have it hooked it stays constant at 29.9k and the more I look at the strips I am thinking it might be either Red Gray Violet Red Brown or Red Gray White Red Brown

    This link should take you to the full sized image if that helps http://postimg.org/image/3w3v1njmh/full/

    I am going to see if I can get some better pictures on the board later today. I looked closely at all the capacitors on the board originally thinking that was the issue since in the past on other projects they seem like the main culprit.

    Thanks again for the the help!
     
  14. Jul 10, 2014 #13

    jim hardy

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    Full size picture sure looks to me like a 28.9k 1%.

    i wonder if the middle white looking band was purple before it got overheated.
     
  15. Jul 10, 2014 #14

    davenn

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    definitely a difficult one


    it really boils down to what that very discoloured centre band was ??


    Here's a table showing all the different resistor ranges

    attachment.php?attachmentid=71210&stc=1&d=1405050614.jpg

    the closest is 287 xOhms


    Dave
     

    Attached Files:

    Last edited: Jul 10, 2014
  16. Aug 2, 2014 #15
    Just wanted to follow up I bought a replacement 28.7K resister soldered it in and everything seems to be working great so far I'll keep an eye on it to watch for any signs of trouble but I think I am good.

    Big thanks to everyone for all the information and insight!

    Jason
     
  17. Oct 18, 2015 #16
    Hi Jason/Abtar,

    I'm also facing exact same issue with my GE microwave?

    What is the wattage of the replaced resistor (28.7k ohms with 1% tolerance)?

    Thanks,
    Sandeep
     
  18. Oct 18, 2015 #17

    davenn

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    going by his photo, it looked to be a 1/4 W
     
  19. Oct 18, 2015 #18
    Thank you for you help Davenn-
     
  20. Aug 1, 2016 #19
    I just fixed my GE Microwave XL 1800 for $2.95. I purchased the 1/4W, 30k Ohm resistor and a 220uf 50V capacitor. Soldered them in, put the WB27X10438 control
    board back into the unit and it works perfectly. The large black power relay is not manufactured anymore so I figured I would replace the capacitor and resistor, if that didn't work I would have to spring 150-160 for a new power control board.

    3.jpg

    9,jpg.jpg
     
  21. Aug 2, 2016 #20

    NascentOxygen

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    If a ¼W resistor is overheating, I'd be tempted to replace it with a higher wattage, say, 1W, but keeping the same Ohms, providing the board can accommodate the bigger size and heavier gauge leads.
     
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