Connect with us

Microwave stays "on" when door closed.

Discussion in 'Troubleshooting and Repair' started by bobbintb, Aug 25, 2019.

Scroll to continue with content
  1. bobbintb


    Aug 25, 2019
    I have a microwave that one day after cooking some food, continued to hum after the timer was done. The humming stops when the door is open and starts again when the door is closed. It didn't take long to realize it was probably still cooking. I put a cup of water in and it confirmed this. Pretty sure a stuck relay is keeping the magnetron engaged and my solution thus far has been a firm smack on the control panel. That fixes it for a while but then it happens some time later. I can't be certain but I think it might have gotten stuck in the "off" position once or twice as well. Once or twice, I thought I put food it, punched in the time, and hit start, only to find it was still cold but I can't be certain it wasn't just old age creeping up on me. The model is SMH1713S and out of warranty. I can't upload the service manual as it is too large at 3MB but here is where I downloaded it from:

    I'm pretty sure the faulty relay is a F5H-DC12V-P1, either RY202 or RY203 in the schematic. I'm just concerned because I don't know much about relays. I don't want to replace them and still have the problem. I don't know if maybe there is a design flaw and replacing the relay is only going to fix it for a while because something else might be causing the relay to fail and I'm only fixing a symptom of the problem. I thought maybe I could get a second look from a more knowledgeable person. I appreciate any help.
  2. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir bobbintb . . . . .

    I must say that model almost has all of the bells and whistles, and I NEVER have seen a manufacture be as generouis with ALL of the tech info.
    I initially am just using the simplest block diagram / photo.
    It also appears to be the main power relay for the magnetron that has time/ service eroded and pitted contacts and its resultant "iffy" contact action. Sometimes not closing to good contact connection and sometimes making a temporary "spot" welding of the contacts. . . .ergo a continual running then..
    Either of those fault modes could be analyzed by simply monitoring the coil of that relay to confirm if there is never being contact continuity on the top two push on contacts without 12VDC relay coil power presence . . . .OR . . . . .an open contacts circuit with 12VDC relay coil power.

    Consulting the full schematic for further analysis, reveals a door locks tandem arrangement of switches that either inhibits operation of the magnetron power or in its other mode, blows the main fuse. So . . . .I guess . . .that that fuse has never blown ?

    Can you view your board, or you may remember from a previous viewing . . . .if there is just the sole presence of relay R202 ? . . . . and not the additional RY203.
    Also note the SM's error on the text balloon . . . which I corrected . . . that had the relays I.D.'s being reversed, compared to the boards symbolization.

    AND did 'ja notice, that its absolute " RELAY CITY" over to the right area !

    I would suggest taking two insulated wires from the the solder connections of the relay coil connection to remote outside the unit to be able to use a meter for monitoring 12VDC presence to that coil.
    Then, if you can repeatedly do turn on short test cycles and catch the unit running when it SHOULD BE OFF , but with no 12VDC relay coil voltage presence . . . the relay contacts are at fault.
    The other situation is the magnetron unit not running when turned on for a cook cycle.
    In this case you could perform a DOUBLE test by having one the remote wires coming out while the other is routed a bit differently.
    You pull off the two switched wires that plug into the top of the relay.
    You now have a power dormant set of relay contacts, one of which will receive the OTHER remoted 12vdc wire into one vacated top relay contact and a new wire connects to the other relay contact.
    You now effectively have one remoted wire remaining as it always was for testing , the other wire connected to one contact at the top of the relay, the newly added wire goes to the other contact and down to the monitoring position as the other needed wire.

    There is a shortcoming of using either an analog meter or DVM in monitoring in their response time. (Vice the aural rsponse of the DVM in its diode / continuity test IF being an available option ? )

    Should you use a LED with a series 470 current limiting resistor . . . . with the pair installed with correct polarity for the incoming 12VDC voltage.
    A visual monitoring of that lit LED will then be able to perceive a relays contact power disruption for as short of a duration as ~100 milliseconds.
    Shorter time than that is a fuzzy situation . . . . . in the respect of the human eyes persistance of vision kicking in.

    This preparation all leads into the final relay testing aspect of having the top cover access open to be able to reach the RY202 relay case .
    You then key in a good known cook cycle , but don't expect the MAGNETRON to respond BUT DO know that R202's coil should be having a 12VDC presence and the LED indicator is lit .

    You then use the plastic handle of a medium size screwdriver *** to tap the side of the RY202 relay case in the same directional plane as the nearby large BLUE filter capacitor pair are.
    (*** Using either a conventional Phillips or Standard slotted blade . . . . . .but I would be a bit wary of a new fangled Torx. )

    Proceed thru a moderate tap to a harder tap to a FIRM TAP, to see if relay contact is disrupted by LED light dropout for that long /or / short of a duration.

    Now if you posess the mechanical aptitude and technical acumen, go DOITTOIT !
    Or . . . . . . ask for any clarifcations . . . .

    Thaaaaaaaaaaaasssit . . . . . .

    Le TECHNO-NIBBLE . . . . . .


    73's de Edd . . . . . .

    Don't EVER find yourself ending up in getting between a dog and a fireplug / utility pole.
    (Hmmmmmmmmm ?. . . . . but then, there ARE times, when a dog thinks that YOU are a fireplug / utility pole ! )

    Last edited by a moderator: Aug 25, 2019
  3. bobbintb


    Aug 25, 2019
    Thanks for the reply. Yes, I was quite pleasantly surprised at how in depth the service manual was. I didn't even have to take it apart to figure out exactly what I needed, where it was, and how to get to it. I hadn't noticed the error in the manual. Good catch. I've never taken it apart so I don't know if it has both relays or not. It used to only do this every so often, like 6 months or so. But it's increasing in frequency. It's happen 3 times just the last few days. You are right, the fuse has never blown.

    That's a very thorough test but I'm not sure if I have that kind of time. Plus I seemed to have misplaced my voltmeter. I just started another semester of grad school and work is picking up and I don't want to get into a situation where I take the microwave apart and don't have to time to get back to it and be without a microwave. I am notorious for leaving things half finished. Since the relays are pretty cheap and it seems to happen much more often, it would be quicker to just replace them both and see if that fixes it. However, your suggestion is definitive and the technician in me prefers definite answers. Do you think there is much risk in that approach? I'm pretty confident that's what the problem is but there is the "I don't know what I don't know" factor.

    Also, I could just get the cheapest relays I can find from some Chinese manufacturer, but perhaps it's worth it to get some quality ones for this application. If I do end up replacing them, what brand should I get? The schematic says the relay is F5H-DC12V-P1.
    Last edited: Aug 25, 2019
  4. 73's de Edd

    73's de Edd

    Aug 21, 2015
    O.K. then if you don't want to do that precse analytical testing . . .just going for broke.
    An AMERIKANSKI sourced . . .equivalent relay could be obtained from either Digi-Key or Mouser as a Panasonic relay for a little less than 3 Amellican dollah.
    Its being Panasonic part number ALE13B12.
    The "not for new use" is just being relevant to them not repating manufacturing runs of that relay and depending upon depleting their existing current stock from them or suppliers having the item in inventory. An end date is given and after that the equivalent unit will be available as a SCHRACK unit.

    Panasonic ALE13B12 from Digi-Key . . . . .

    Panasonic ALE13B12 from The Mouse House . . . . . .

    Panasonic Manufacturer Data Sheet for ALE13B12

    The unit that will be replacing it is the RZF1-1A6-L012 and it is already available in stock.

    Panasonic RFZ1-1A6-L012 from The Mouse House . . . . . .

    Go for it . . . . .
  5. bobbintb


    Aug 25, 2019
    Well, it's more of an issue with having the time to be that precise than what I prefer. Thanks for the links. I was looking on Mouser but I'm not familiar enough with relays to find it if goes by a different name or number so I couldn't find what I needed. I was talking to the manufacturer too and even though the warranty expired 5 years ago, they might send someone to fix it for free. I guess they don't want the liability, lol. That definitely takes me less time, but I was kind of looking forward to doing it myself. I guess I'll have to wait and see what they say. Thanks for the super-detailed help.

    Edit: Are you sure RZF1-1A6-L012 is the right one? The mounting style is panel and the ALE13B12 is through hole. The resistance is also lower, not sure if that matters for this.
    Last edited: Aug 27, 2019
  6. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir bobbintb . . . . .

    Somehow ? . . . . .I want to think that you haven't even cracked the covers of that unit for board inspection.

    Thus, confirming that it only has one main power relay.

    The original relay has the two PUSH on top wired clinch connectors, permitting some HEAVY current handling in a short route to the internal contacts of the relay. It only needs 10A capacity at high power and the relay is generously rated at 16A .
    The bottom of the relay has the coils two side by side pins at one end of the bottom of the relay for solder connection to the PCB .
    There is one additional " guide pin" on one corner of the opposite sidw of the relay, that connects to the HOT switched AC line connection, however I don't think that any active connection is being made into that connection .

    On your . . . .

    Edit: Are you sure RZF1-1A6-L012 is the right one? The mounting style is panel and the ALE13B12 is through hole. The resistance is also lower, not sure if that matters for this.

    They have two connections coming out the bottom, of which you are expectted to clip off the one that is additional and will not have a hole on the PCB for that pins passage.

    The resistance is also lower, not sure if that matters for this.

    Only assuring a more POSITIVE contact pressure.

    The mounting style is panel . . . .

    ¿ ¿ ¿ panel ? ? ?

    REF . . . . .

    Is where I am seeing thru hole pins.

    73's de Edd . . . . .

    Copywight 2019 by Elmer Fudd. All wights wesewved.
  7. bobbintb


    Aug 25, 2019
    No, I haven't opened it yet. I just haven't had the time and knowing myself, if I start on it and don't have enough time, it will just stay taken apart forever.

    The reason I ask is because on the product page in the middle under "Specifications" is where it says "panel" and the other is "through-hole". It might just be an error on the product page.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day