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Dodgy Dishwasher Controller

Discussion in 'Power Electronics' started by Pineapple32, Aug 29, 2019.

  1. Pineapple32

    Pineapple32

    1
    0
    Aug 29, 2019
    Hi Guys,

    Would appreciate some advice, please be gentle!

    Dishwasher stopped working, no lights on controller at all, only thing I could see that had failed on the board was a 100R 5% 3w resistor.

    I since replaced this with another 100R 5% 3w resistor and when I applied power it arced and failed.

    Only difference in the resistors was the existing I believe was wire wound and my replacement was metal oxide, would this make any difference??

    I have attached a photo for reference, resistor in question is R45.

    Image: https://ibb.co/qjQNs5r

    Thanks in advance!
     
  2. Alec_t

    Alec_t

    2,658
    700
    Jul 7, 2015
    Welcome to EP!
    Your linked pic is too blurred to be useful. A sharp png format pic posted to this site would be better.
    The resistor failure was probably due to some other component (e.g motor or heater) drawing excess current.
    Is there any pcb charring/discolouration or other evidence to suggest that R45 has been overheating for a long period?
     
  3. dave9

    dave9

    770
    171
    Mar 5, 2017
    ^ The hosting site is doing something screwy, softening the image after downsampling it.

    Click the link on the pic and it becomes a nice, crisp, 16MP resolution. Unfortunately, I don't see any visual signs of a problem besides the burn mark on the resistor itself... can't even see the traces going to it.

    You could check the wiring going to the heating element in case it has shorted against something, or perhaps the heating element itself has somehow come loose, and the same for the motor wiring.

    If it's a 125V motor you could even apply mains voltage directly to it to see if it works, but I leave it to you to decide if you want to be working with live mains voltage.

    You could check for a shorted pump, solenoids, etc... anything you can leave unplugged while applying power to the board will rule out each item in turn.

    Personally I would put a fuse on the mains circuit to it (make an extension cable with an inline fuse, unless it is hard wired then you need a junction box with a fuse) so you blow the fuse instead of continuing to blow resistors and stressing who knows what else in the process.

    How old is the dishwasher? Any chance of getting a repair manual or schematic? Might it be time to just replace it? IMO they are built to self destruct, seals get worn and hot steam goes everywhere.
     
  4. Alec_t

    Alec_t

    2,658
    700
    Jul 7, 2015
    An internal short in the heating element is a common fault.
     
  5. dave9

    dave9

    770
    171
    Mar 5, 2017
    ^ Isn't the element itself just a large resistive metal rod that can't short out unless there is some other mechanical damage to the assembly causing it to short against something else? I'm trying to understand how it can short out internally.
     
  6. Alec_t

    Alec_t

    2,658
    700
    Jul 7, 2015
    No. It might look like just a rod, but what you see is only the tubular sheath (which is grounded). The resistive part is a thin wire through the sheath core and spaced from the sheath wall by compacted insulating mineral powder. A pinhole in the sheath can admit water, with obvious (and sometimes spectacular) consequences. I once had an immersion heater element blow its sheath apart.
     
    Last edited: Aug 30, 2019
  7. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir Pineapple32 . . . . .

    You say . . .

    I since replaced this with another 100R 5% 3w resistor and when I applied power it arced and failed.

    We l l l l l l l l l l, that is because that there is being one SEVERE (x100) overloading of it in the load circuitry on down the power stream from it.
    The original was a metal film type also.
    Look in the direction of the nearby flexible ribbon cable and note that there is being a " wannabe" 8 pin dip that is centered upon that cable on the close side.
    Come back with that part number which is marked upon it. Possibly being a VI-per number series.

    My eagle eye 20-18 vision has time deteriorated, down to a now mere 20-19.
    But with your vewy-vewy close in inspection, might also reveal that the case of that I.C. has a top side carbon cavity developed within it from a vaporized power FET enclosed internally.

    Get that info and we will continue after my timely departure for being a great great grand Chauffer for a short . . . kiddos . . . . delivery trek.
    Also, another good photo, incorporating a less encompassing view of only that quadrant of the PCB might be helpfull.

    Thaaaaaaasssssit . . . . .


    73's de Edd . . . . .

    Once when I was lost as a " mean widdle " kid , I saw a policeman, and asked him to help me find my parents.
    I said to him, "Do you think we'll ever find them? "
    He then said, "I don't know kid . . . . . . there's s o o o o o o o o o many places they can hide."




    .
     
    Last edited: Aug 30, 2019
  8. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir Pineapple32 . . . . .

    He's ba a a a a a ck . . . . .
    Pick up and deliveries of the rug rats accomplished . . . . .

    MY CONTINUANCE . . . . .

    I can now acknowledge that a LNK305GN is being incorporated, as is now clearly revealed, by using the Hi def viewing option of your submitted photo .

    Lets just use a published manufacturers devices application sheet, in fulfilling the needs of a comparative schematic to work with.

    REFERENCE TO . . . . . . . . .

    http://www.mouser.com/ds/2/328/lnk302_304-306-179954.pdf

    Then, if you will concentrate and " constipate " on page 5 of that reference for the crux of that info, it therefore will then save me tew ' tousand keystrokes of any explanations.
    And you will then be fully Edd-i-cated on how that " power supply " in a chip operates.

    One observational point of contention is being the Resistor Fusible 1 value of resistance . The typical value used for that is being 1/10th of your currently selected value. Although, the photo does ¿ seem ? to be showing a BROWN third color code band.
    BUT is that photo showing the original part or your replacement part ? J ust by the basic grey body color I am wanting to think that is the original board resistor.
    My current finds in metal replacement units, seeem to tend to be having blue or reddish brown or green body colors.
    Your first exploratory task will be to take the ORIGINAL resistor and if being the one in the photo, with the point of failure being in the RED X area.
    Clean the lead ends for getting a good connection and then get DVM and switch into low ohms mode and short the test probes together to get a readout of the total lead and connector contact resistances in that measured loop . . . log it down or commit to memory.
    Then take the lead the most distant from that black burn out mark on the resistor and grip that resistor lead to one of the meter leads.
    Hopefully the other free leads probe tip will be somewhat pointed, in order to be able to position it at the mid point of the resistor and do a pressured and rotating and rocking action to start grinding into and displacing that conformal epoxy coating . Expecting the tip to come into the radially laid out spiral winding of the metal resistance film on an inner round ceramic bisque form.
    It possibly might take 2 side by side attempts, but that half should be ohmically intact, since the blowout was being on the other half.
    I am fullly expecting your then acquired ohmmic readout + the lead resistance to be ~ 1/2 of the resistors actual value . . . . . with my leaning being towards it being a 5 ohm value instead of 50 ohms.
    My thinking is being influenced by the reference schematics 8.2 ohms.
    Whatever it turns out to be, there was some fault developed within my marked in Yellow Brick Road (arrows) path, so that that all of those components were subjected to overloading, up to the final point where that fusible resistor then opened up.

    upload_2019-8-31_8-32-41.png

    THEN . . . your " ants in the pants syndrome ". . . / . . . INSTANT gratification . . . or . . . naivety, resulted in the same system components in that loop, having to be SEVERELY overtaxed, yet again!.
    You SHOULD have temporarily inserted a series wired 60 watt incandescant lamp, within the very top HOT AC line input.
    Then, on an initial shakedown test, the presence of a severe overload or short will then only result in the lamp taking the overload situation by merely lighting up vewy-vewy bwightly.
    Its developed high resistance and power consumption then limits power getting on down to the subjective loop components.
    .
    The next analytical test willl involve the testing between the marked in RED X test points assigned to the Drain Source connections of the internally contained power FET within the LNK305.
    Know what ? . . . . somehow, I'm fully expecting it to be dead shorted.

    I now turn the board analysis back to you . . . . . for your resultant finds . . . . . .

    ASIDE . . . . Main Photo
    The Roadrunner says "BEEP ! - BEEP ! " zoooooooooooooom . . . . . to the 06L Piezo alert transducer, in the top left corner.

    MARKED UP BOARD REFERENCING . . . . . some relative / coincident schematic assignments have been labelled onto your board components

    upload_2019-8-31_8-46-47.png




    73's de Edd . . . . .


    Speaking of unbridled sheer gullibility . . . . .

    Did you hear about the $3 million West Virginia State Lottery? The winner gets $3.00 a year for a million years. . . .
    (SUCH . . .a deal . . . already! )


    .
     

    Attached Files:

    Last edited: Aug 31, 2019
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