Resistor ID help

Discussion in 'Datasheets, Schematics, Manuals and Parts' started by Rastus, Jul 16, 2017.

  1. Rastus

    Rastus

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    1. Hello all...I am hoping someone can positively identify this component. It is from the control board of an ONAN generator (Mod# 5BGMFA26105D). It is 1cm square, and marked MCI 2-0 (or maybe MOI 2-0). It is reading 0 ohms. The location screening on the board is RS1. I think it may be a metal film resistor, but the RS designation makes me wonder. There are a couple of "regular" resistors on the board and they are denoted R1 & R2. I haven't been able to find a schematic for the board. It looks like this to connected from 12V to a run-time meter and "on" indicator lamp when the generator is running

    Onan Resistor.jpg
     
    Last edited by a moderator: Jul 16, 2017
    Rastus, Jul 16, 2017
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  2. Rastus

    Harald Kapp Moderator Moderator

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    Your photo has not enough resolution to allow identification of the component.
    From the size and the marking RS I take it this may be a shunt resistor used to measure current. Usually such a shunt resistor would have a value less than 1 Ω, more in the range of a few mΩ, depending on the current being measured.

    Would this page be of help to you?
     
    Harald Kapp, Jul 16, 2017
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  3. Rastus

    Rastus

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    Thanks Harald for the response. I have that bookmark and it is useful for getting the gist of how Onan's control boards work, however none of the schematics presented show my control board and/or this particular part of the circuit. My meter is pretty accurate and the resistor looks like a dead short. So do you think the MCI 2-0 marking on it could indicate something like .2 ohms or even .02?
     
    Rastus, Jul 16, 2017
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  4. Rastus

    Harald Kapp Moderator Moderator

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    A resistance of 0.2 Ω or 0.02 Ω will look like a short to most inexpensive multimeters. You'd need a rather precise instrument, preferably with a Kelvin connection to measure such a resistance relialbly.
    The resolution of yur photo is too low to allow me to judge the lettering on the component. Give it another try and make a macro shot which shows the marking as clearly as possible, then upload the new photo.
     
    Harald Kapp, Jul 16, 2017
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  5. Rastus

    tedstruk

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    I make it a habit not to mess with control boards unless absolutely necessary.
    The placement of this component on the control board will probably give some hint as to what it is supposed to do. Its hard to tell what a component is even with a schematic, unless some poor sap (lmao) took the time to label all the components...
    That looks like a switching cap. I wouldn't put any resistor in there until you are sure
     
    tedstruk, Jul 16, 2017
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  6. Rastus

    tedstruk

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    tedstruk, Jul 16, 2017
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  7. Rastus

    Rastus

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    RS1_a (2).jpg
    View attachment 35207

    Hope these shots are are a little better...the marking is extremely faint. My Fluke is pretty accurate down to 0.00 ohms. I'm going to try to find a couple of low value resistors in my bone pile for comparison.
     

    Attached Files:

    Rastus, Jul 16, 2017
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  8. Rastus

    Rastus

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    @tedstruk ... thank you for your replies. The control board part number this part came from is 300-3764. The link you provided has no info on this particular board. You show me an accurate schematic, I can take it from there:D. One side of this "doohickie" is connected to 12V (off of the run relay), and the other supplies the Hobbs meter and a lamp that indicates the genset is running. I doubt that it's a cap.
     
    Rastus, Jul 17, 2017
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  9. Rastus

    Harald Kapp Moderator Moderator

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    This photo is so much better!
    Unfortunately it doesn't help me identify the component. I'm sorry. A schematic would be really helpful. Funny that there are schematics for many other generators from this company but none for your specific model :(
     
    Harald Kapp, Jul 17, 2017
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  10. Rastus

    Richard9025

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    The model 5BGMFA26105D leads me to the ONAN MARQUIS 5000 series
    I was able to find a looong service manual, featuring schematics, wiring diagrams and much more for the marquis series of these generators
    See if it looks like your unit:
    http://www.twinslan.net/~n0nas/manuals/onan/965-0531B Onan BGM NHM Marquis series RV Genset Service manual (02-1991).pdf
    Even if it is not your unit, maybe it helps

    I was looking in it and I found these things:
    vef260-1 - Copy.jpg
    And a schematic featuring RS1 in 4 different ways:
    Look for the A1-RS1 (middle to right), the first schematic doesn't show it, only the other three
    There are many schematics in the service manual (look at the last pages), be sure to read it !
    965-0531B Onan BGM NHM Marquis series RV Genset Service manual (02-1991)-129.jpg
    965-0531B Onan BGM NHM Marquis series RV Genset Service manual (02-1991)-130.jpg
    965-0531B Onan BGM NHM Marquis series RV Genset Service manual (02-1991)-132.jpg
    965-0531B Onan BGM NHM Marquis series RV Genset Service manual (02-1991)-133.jpg


    You can see RS1 in the schematics, (middle) it looks like a resistor.
    There is MUCH more info in the service manual, be sure to look into it.
     
    Last edited: Jul 17, 2017
    Richard9025, Jul 17, 2017
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  11. Rastus

    73's de Edd

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    Sir Rastus . . . .Festus here . . . .

    I'm thinking that is being a 2A Resettable poly switch.
    Can you establish a shorted probes condition on your Fluke . . . .Duke . . . . in its low ohms mode and find the series loop resistance, and then measure the dee-vice and come up with its closest resiatance value and then deduct the error resistance.( COURSE , if you gots the DEE-LUXE . . . . .wun hunna dollah . . . FLUKE, that is being its initial autocorrect /zeroing feature.)
    Then reinstall the dee-vice and fire up ye olde gen unit and take . . . . what should probably be in DC millivolts . . . the voltage reading across it.
    Use your found resistance and compute current value with your just established V and R values.
    Isn't it falling in as being less than 2 amps . . .or ~1 ?
    If so, it is then probably safe to pull the unit again and sub in your FLUKE in DC 10 amps range with the + test lead properly moved and double checking proper switch setting and see what current passage doth lie therein.
    If all of thiis tallies out, me thinks that you just done gots yersefs a "durty" [ Texan au Texan ] (cosmetically that is ) but, probably GOOD, polyswitch .
    To upstage testing, yet one echelon higher, pull and use a 12VDC source that is hefty enough to drive 3 amps through a 4Ω at ~ 40 watt wirewound resistor in series with the polyswitch for about 15 seconds..
    ( 60 somewhat years ago I had to replace a clothes drier heating element, that same unit, along with two allimagator clipped test leads, has since, always been my variable POWER LOAD BANK.)
    [ Some auto tail light/stop/turn bulbs or park lights have current pull levels that also create good power test loads.]

    See if that puppy doesn't go open circuit at ~ 3A, or for sure at a quick 4A and then reset after a proper cool down.

    If so . . . . . . direct your sleuthing elsewhere.

    ADDENDA:
    I see that The Most Honnable Sir Richard the Ist . . . . .has added on here, while I was doing my poking up and researching.
    I have never had any need to use this symbol but . . .voilà

    .[​IMG]


    73's de Edd
     
    Last edited by a moderator: Jul 17, 2017
    73's de Edd, Jul 17, 2017
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  12. Rastus

    davenn Moderator

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    well with the bar through it, it suggests a varistor or thermistor

    Edd beat me to it :)
     
    davenn, Jul 17, 2017
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  13. Rastus

    Rastus

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    Thank you Richard! A schematic!:D Now I can put this interesting little polyswitch back where it belongs and get to solving whats wrong with my generator. I have looked and looked for an online manual for this model, and never came across Twinslan. ...and a big HOWDY from this Texan to you and your Romanian neighbors!
     
    Rastus, Jul 17, 2017
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  14. Rastus

    Rastus

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    FestusEdd, pleased to make your acquaintance! The entertainment value of your reply almost equals the informational content;). I'm glad that Richard came through with a schematic, so I don't need to subject this little fella to all that pokin' and proddin'. Hmmm...a 60 some-odd year old dryer element - I bet your garage looks as bad as mine. Thanks again for your input!
     
    Rastus, Jul 17, 2017
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