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Need Help Fixing Kenmore microwave-Hood 721.62752100

Discussion in 'Troubleshooting and Repair' started by smurfboy, Mar 15, 2007.

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  1. smurfboy


    Mar 15, 2007
    I bought this unit 3 years ago for $400 and it has served my grandparents needs well. The other day it stopped working and I need help on trying to get it back up and running.
    Here's the problem.. It looks fine and the control panel and clock works fine. When I put something in it to cook, the light comes on and so does the fan BUT the carassel no longer turns and it wont cook/heat anything up any longer.

    I'm Stumped here and I have called Kenmore and they have suggested I just throw it away and buy a new one which will cost my grandparents 100's of dollars again. And my grandparents can't afford to keep paying for a new microwave every 3 years..

    Please HELP.....
  2. Farentino


    Oct 4, 2015
  3. davenn

    davenn Moderator

    Sep 5, 2009
    sorry, I cant find any specific info on that unit ... I cant even find a pic of what it looks like
  4. GPG


    Sep 18, 2015
    Do you hear a relay click when the start is pressed?
  5. 73's de Edd

    73's de Edd

    Aug 21, 2015

    Sirs smurfboy . . . . . .davenn. . . . .GPG . . . etal . . . .

    Why . . .shore they do . . at . . . .

    and you can even try their dog and pony repair act.

    Seems like all of my friends- colleagues-neighbors -relatives have me corralled into being their go to guy on any electro-mechanics repair.
    And on most of the late microwaves I have seen their weak link seems to be the power relay that switches the power to the units big ole magnetron power transformer.

    Supposedly this is the updated and latest control board ( numbered at the side) for that SAME microwace that is tri-branded as both Sears Kenmore-Maytag and supposedly actually being an LG derivation.

    Original control board 6871W15045A is OUT OF STOCK . . .until ? ? ? ( that telling you anything ?)

    Look below and you will see a bevy of smaller relays on the board, but the ONE of interest is my marked up unit . . . .dat unit has to pass almost a 'tousand watts . . . . babycakes !

    I believe that the all important power magnetron ands its HV power rect diode are intact, but you might look for a hi amp white ceramic fuse and pull it and check for its ohmmic continuity.

    If the oven REPEATEDLY fails, and is not hit and miss, that would be conducive of testing my mentioned relay.
    I am thinking that power comes in, to one of the push on terminals and passes thru the relay contacts and goes out the other push on terminal, to feed the power transformer.
    Thereby that would leave no AC power on the relay terminals if those wires are pulled off.

    SAFETY FIRST . . . . if metering high voltage . . . .keep one hand in your pocket . . . .and one leg in your pants.
    (But I think that I have procedurally relieved you of having to touch any circuitry, while testing in power on mode,)

    To test the relay pull AC cord and cabinet dust cover and get access to the depicted PCB and pull the magnetron relays two push on wires and put a snug fitting vinyl sleeve over both for safety or SECURELY do an insulate/ tape/wrap on them and even further . . . tape the pair to MW cabinetry wall so that they are even further isolated from any possible contact.

    Use insulated clip/test leads to make a connection to each of the relays now exposed terminals and the other ends of the clip leads go to the metering terminals of a VOM-DVM set on the closest range that exceeds 125 VAC I say VAC because we initially want to be dead dog sure that no power is on that terminal pair.
    ( A dollar/Euro sez that there certainly isn't)

    Power up the unit and see that all functions that initially worked, still do so.
    Then . . . .AND THEN ! . . . you power down, if no 125 VAC was metered, and then you switch to low ohms scale , it should be showing show no relay contacts connectivity.

    Get ready to now Power up the MCW and, we now have two things to check, set in 10 seconds of cook time and activate the unit to see if the ohms reading is still infinity or has dropped to very low ohms and is showing a connection . If so, this relay is good UNLESS it has blackened / pitted contacts and arcs and won't pass full wattage.
    If the relay produces no low ohms, when powered on, then you may have also heard the solid clunk of that mag power relay at turn on time, from its internal armature pulling down.
    That verifies 12V drive power getting to its coil.
    Another relay coil test if you did not HEAR it thump at start of cook time, is to put a finger atop the relay to feel for the vibration produced by the mechanical thud of the armature when it is initially activated.
    We need to know that coil power to activate the relay is present.Otherwise, no voltage to the relay coil would also cause NO closing action of its power contacts.

    So . . . in reviewing . . . . we need to know that the relay is thumping at cook time activation and if the contacts close after thumping.
    If NO power relay contact closure after thumping, methinks . . . . we probably done gots ourselves an easy fix !

    The only power on that relay is a low control voltage of 12 V, if the push on terminals are removed .

    I'm to the point where I now need your feedback . . . . .standing by . . . . .

    Le image du . . . . . Control board :


    73's de Edd

    Arouse1973 likes this.
  6. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Might want to check (or is that "cheque" 73's de edd?) the door switch contacts as well. If it was the relay, diode or magnatron, I'd expect the turntable to spin normally.
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