My kitchen's electric oven is misbehaving. After it's been on for a while, it can make a buzzing noise, and its LCD (?) flickers. Eventually it shuts off, resets itself, and restarts with a "Program Cancelled" message. Clearly, its microcontroller knows that it was previously running. This is not like a power-on reset. The buzzing sounds a bit like a relay that's receiving so little coil current that voltage ripple makes it buzz. I've come across that before, and this thing contains several relays. The obvious thought is dying electrolytic capacitors, but failing when it's got warm doesn't fit my understanding of such capacitors which would be expected to perform better when warm, even if they've aged to the point where they're no longer adequate. Any thoughts? Sylvia.
Oven problem
Started by ●December 25, 2021
Reply by ●December 25, 20212021-12-25
On a sunny day (Sat, 25 Dec 2021 22:17:48 +1100) it happened Sylvia Else <sylvia@email.invalid> wrote in <j2ocutFndc7U1@mid.individual.net>:>My kitchen's electric oven is misbehaving. After it's been on for a >while, it can make a buzzing noise, and its LCD (?) flickers. Eventually >it shuts off, resets itself, and restarts with a "Program Cancelled" >message. > >Clearly, its microcontroller knows that it was previously running. This >is not like a power-on reset. > >The buzzing sounds a bit like a relay that's receiving so little coil >current that voltage ripple makes it buzz. I've come across that before, >and this thing contains several relays. > >The obvious thought is dying electrolytic capacitors, but failing when >it's got warm doesn't fit my understanding of such capacitors which >would be expected to perform better when warm, even if they've aged to >the point where they're no longer adequate. > >Any thoughts? > >Sylvia.If you have a scope measure the ripple voltage on those electrolytic caps Also in most cases with faulty wallwarts I have seen the bad caps are a bit swollen at the top. _____ (_____|========= . / \ |
Reply by ●December 25, 20212021-12-25
On 25-Dec-21 10:17 pm, Sylvia Else wrote:> My kitchen's electric oven is misbehaving. After it's been on for a > while, it can make a buzzing noise, and its LCD (?) flickers. Eventually > it shuts off, resets itself, and restarts with a "Program Cancelled" > message. > > Clearly, its microcontroller knows that it was previously running. This > is not like a power-on reset. > > The buzzing sounds a bit like a relay that's receiving so little coil > current that voltage ripple makes it buzz. I've come across that before, > and this thing contains several relays. > > The obvious thought is dying electrolytic capacitors, but failing when > it's got warm doesn't fit my understanding of such capacitors which > would be expected to perform better when warm, even if they've aged to > the point where they're no longer adequate. > > Any thoughts? > > Sylvia.Thanks for the replies. My diagnosis is a burnt-out fan motor. This fan is meant to keep the electronics cool. Sylvia.
Reply by ●December 26, 20212021-12-26
On Sat, 25 Dec 2021 22:17:48 +1100, Sylvia Else <sylvia@email.invalid> wrote:>My kitchen's electric oven is misbehaving. After it's been on for a >while, it can make a buzzing noise, and its LCD (?) flickers. Eventually >it shuts off, resets itself, and restarts with a "Program Cancelled" >message. > >Clearly, its microcontroller knows that it was previously running. This >is not like a power-on reset. > >The buzzing sounds a bit like a relay that's receiving so little coil >current that voltage ripple makes it buzz. I've come across that before, >and this thing contains several relays. > >The obvious thought is dying electrolytic capacitors, but failing when >it's got warm doesn't fit my understanding of such capacitors which >would be expected to perform better when warm, even if they've aged to >the point where they're no longer adequate. > >Any thoughts? > >Sylvia.The relay coils are copper, which increases in resistance by about +.4%/�C. Relays are *current operated* devices (ampere*turns) that happen to be specified in terms of nominal operating voltage. So if the power supply is marginal the relay might not pull in when it's warm. I would guess the capacitors are the culprit. -- Best regards, Spehro Pefhany
Reply by ●December 26, 20212021-12-26
In article <j2ocutFndc7U1@mid.individual.net>, Sylvia Else <sylvia@email.invalid> wrote:>The obvious thought is dying electrolytic capacitors, but failing when >it's got warm doesn't fit my understanding of such capacitors which >would be expected to perform better when warm, even if they've aged to >the point where they're no longer adequate. > >Any thoughts?Could still be bad caps, could be cracked/broken solder joints on the PC board, loose or intermittent cable connections. If a replacement controller board isn't available, then an R&R of all of the electrolytic caps (use good-brand 105C or better), and inspection of all solder joints (especially those on connectors) and a touch-up of any questionable ones with proper solder and flux would be what I'd probably try.
Reply by ●December 27, 20212021-12-27
On 25/12/2021 9:17 pm, Sylvia Else wrote:> My kitchen's electric oven is misbehaving. After it's been on for a > while, it can make a buzzing noise, and its LCD (?) flickers. Eventually > it shuts off, resets itself, and restarts with a "Program Cancelled" > message. > > Clearly, its microcontroller knows that it was previously running. This > is not like a power-on reset. > > The buzzing sounds a bit like a relay that's receiving so little coil > current that voltage ripple makes it buzz. I've come across that before, > and this thing contains several relays. > > The obvious thought is dying electrolytic capacitors, but failing when > it's got warm doesn't fit my understanding of such capacitors which > would be expected to perform better when warm, even if they've aged to > the point where they're no longer adequate. > > Any thoughts? > > Sylvia.Call an authorized repairer. They will have seen the problem before and come with all parts required for repairs. Fast repair, no sweat. Also, even if you are eminently qualified to do such a repair, if an insurance company wants to fight paying out (say for example, your house burns down for some other reason) they may try to say the fire started with the oven and it was your fault because you were not authorized to do the repair and did not use authorized components. It does not happen often, but it does happen. We live in an age of compliance and legal liability not the past age of competence and ability -
Reply by ●December 27, 20212021-12-27
On 27-Dec-21 7:01 pm, David Eather wrote:> On 25/12/2021 9:17 pm, Sylvia Else wrote: >> My kitchen's electric oven is misbehaving. After it's been on for a >> while, it can make a buzzing noise, and its LCD (?) flickers. >> Eventually it shuts off, resets itself, and restarts with a "Program >> Cancelled" message. >> >> Clearly, its microcontroller knows that it was previously running. >> This is not like a power-on reset. >> >> The buzzing sounds a bit like a relay that's receiving so little coil >> current that voltage ripple makes it buzz. I've come across that >> before, and this thing contains several relays. >> >> The obvious thought is dying electrolytic capacitors, but failing when >> it's got warm doesn't fit my understanding of such capacitors which >> would be expected to perform better when warm, even if they've aged to >> the point where they're no longer adequate. >> >> Any thoughts? >> >> Sylvia. > > Call an authorized repairer. They will have seen the problem before and > come with all parts required for repairs. > > Fast repair, no sweat. > > Also, even if you are eminently qualified to do such a repair, if an > insurance company wants to fight paying out (say for example, your house > burns down for some other reason) they may try to say the fire started > with the oven and it was your fault because you were not authorized to > do the repair and did not use authorized components. It does not happen > often, but it does happen. > > We live in an age of compliance and legal liability not the past age of > competence and ability -I live in Australia. Insurers don't get to pull that nonsense here. As for arriving with the required parts, they don't do component level repair, and it's unlikely boards are still available for this oven, which is probably more than 15 years old. Sylvia.
Reply by ●December 27, 20212021-12-27
On Sunday, December 26, 2021 at 2:13:33 AM UTC, Sylvia Else wrote:> On 25-Dec-21 10:17 pm, Sylvia Else wrote: > > My kitchen's electric oven is misbehaving. After it's been on for a > > while, it can make a buzzing noise, and its LCD (?) flickers. Eventually > > it shuts off, resets itself, and restarts with a "Program Cancelled" > > message. > > > > Clearly, its microcontroller knows that it was previously running. This > > is not like a power-on reset. > > > > The buzzing sounds a bit like a relay that's receiving so little coil > > current that voltage ripple makes it buzz. I've come across that before, > > and this thing contains several relays. > > > > The obvious thought is dying electrolytic capacitors, but failing when > > it's got warm doesn't fit my understanding of such capacitors which > > would be expected to perform better when warm, even if they've aged to > > the point where they're no longer adequate. > > > > Any thoughts? > > > > Sylvia. > Thanks for the replies. > > My diagnosis is a burnt-out fan motor. This fan is meant to keep the > electronics cool. > > Sylvia.Ah, so you've determined that the fan was the cause? I take it this is an "in wall" unit, not a free-standing oven (= "range" in the U.S., with stove top). Being an in-wall type makes sense to me it needs a cooling fan. The "range" types put all the electronics in separate housing away from the heat. FWIW, my first guess was going to be: Check the AC mains line voltage (easier than opening up the oven...) Maybe its low "brown out", due to faulty wiring or circuit breaker, or excessive loading on that branch.
Reply by ●December 27, 20212021-12-27
On 27-Dec-21 7:12 pm, Rich S wrote:> On Sunday, December 26, 2021 at 2:13:33 AM UTC, Sylvia Else wrote: >> On 25-Dec-21 10:17 pm, Sylvia Else wrote: >>> My kitchen's electric oven is misbehaving. After it's been on for a >>> while, it can make a buzzing noise, and its LCD (?) flickers. Eventually >>> it shuts off, resets itself, and restarts with a "Program Cancelled" >>> message. >>> >>> Clearly, its microcontroller knows that it was previously running. This >>> is not like a power-on reset. >>> >>> The buzzing sounds a bit like a relay that's receiving so little coil >>> current that voltage ripple makes it buzz. I've come across that before, >>> and this thing contains several relays. >>> >>> The obvious thought is dying electrolytic capacitors, but failing when >>> it's got warm doesn't fit my understanding of such capacitors which >>> would be expected to perform better when warm, even if they've aged to >>> the point where they're no longer adequate. >>> >>> Any thoughts? >>> >>> Sylvia. >> Thanks for the replies. >> >> My diagnosis is a burnt-out fan motor. This fan is meant to keep the >> electronics cool. >> >> Sylvia. > > Ah, so you've determined that the fan was the cause?"determined that it was the cause" is perhaps over stating it, but the fan is clearly broken, and without it the electronics bay was heating up. Jasen's suggestion that a regulator would go into thermal limiting is then entirely plausible. It would also explain why I could never reproduce the issue with the cover off - the extra ventilation was keeping the temperature down. I'm left wondering whether I previously just failed to notice the fan wasn't running, or whether the fault was somehow intermittent. I'll probably never know now.> I take it this is an "in wall" unit, not a free-standing oven > (= "range" in the U.S., with stove top). Being an in-wall > type makes sense to me it needs a cooling fan. The > "range" types put all the electronics in separate housing > away from the heat.Yes. Sylvia.
Reply by ●December 27, 20212021-12-27
On Mon, 27 Dec 2021 19:35:08 +1100, Sylvia Else <sylvia@email.invalid> wrote:>On 27-Dec-21 7:12 pm, Rich S wrote: >> On Sunday, December 26, 2021 at 2:13:33 AM UTC, Sylvia Else wrote: >>> On 25-Dec-21 10:17 pm, Sylvia Else wrote: >>>> My kitchen's electric oven is misbehaving. After it's been on for a >>>> while, it can make a buzzing noise, and its LCD (?) flickers. Eventually >>>> it shuts off, resets itself, and restarts with a "Program Cancelled" >>>> message. >>>> >>>> Clearly, its microcontroller knows that it was previously running. This >>>> is not like a power-on reset. >>>> >>>> The buzzing sounds a bit like a relay that's receiving so little coil >>>> current that voltage ripple makes it buzz. I've come across that before, >>>> and this thing contains several relays. >>>> >>>> The obvious thought is dying electrolytic capacitors, but failing when >>>> it's got warm doesn't fit my understanding of such capacitors which >>>> would be expected to perform better when warm, even if they've aged to >>>> the point where they're no longer adequate. >>>> >>>> Any thoughts? >>>> >>>> Sylvia. >>> Thanks for the replies. >>> >>> My diagnosis is a burnt-out fan motor. This fan is meant to keep the >>> electronics cool. >>> >>> Sylvia. >> >> Ah, so you've determined that the fan was the cause? > >"determined that it was the cause" is perhaps over stating it, but the >fan is clearly broken, and without it the electronics bay was heating >up. Jasen's suggestion that a regulator would go into thermal limiting >is then entirely plausible. > >It would also explain why I could never reproduce the issue with the >cover off - the extra ventilation was keeping the temperature down. > >I'm left wondering whether I previously just failed to notice the fan >wasn't running, or whether the fault was somehow intermittent. I'll >probably never know now. > >> I take it this is an "in wall" unit, not a free-standing oven >> (= "range" in the U.S., with stove top). Being an in-wall >> type makes sense to me it needs a cooling fan. The >> "range" types put all the electronics in separate housing >> away from the heat. > >Yes. > >Sylvia.They're 'usually' pretty quiet and hidden. though they might get noisier before seizing up. If the coil's not actually fused open, it just needs a bit of cleaning. RL
