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| Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Sharp Microwave powers down after 40 seconds, need assistance
Sharp Model R1810 Carousel II microwave starts and cooks(heats) but
shutsdown after about 40 seconds. Electronic control board display stays lit, countdown stops and displays remaining time--magnetron cooling fan works during the first 40 seconds but then shutsoff--just before shutdown, fan speed increases(doubling or tripling in speed) These items seemed to check out good with VOM-- power fuse interlock switches (2) monitor switch capacitor diode thermal cutout switch(only found one) fan motor power tranformer Additional trouble shooting note--a power surge protector I had plugged the microwave into was discovered fried--suspect a near by lightning strike? Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks |
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#2
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"electroninja" writes:
Sharp Model R1810 Carousel II microwave starts and cooks(heats) but shutsdown after about 40 seconds. Electronic control board display stays lit, countdown stops and displays remaining time--magnetron cooling fan works during the first 40 seconds but then shutsoff--just before shutdown, fan speed increases(doubling or tripling in speed) These items seemed to check out good with VOM-- power fuse interlock switches (2) monitor switch capacitor diode thermal cutout switch(only found one) fan motor power tranformer Does it do the same thing if set to defrost so that the magnetron only runs for a few seconds/30 seconds? Can it be restarted immediately? How is the behavior different than if the STOP button was presssed (maybe aside from the fan speed)? Isn't the fan simply on the AC line so how would its speed change? Or, is it a multispeed fan? --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. Additional trouble shooting note--a power surge protector I had plugged the microwave into was discovered fried--suspect a near by lightning strike? Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks |
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#3
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Ref your questions Sam:
Q. Does it do the same thing if set to defrost.. A. Yes, will run longer in the cycle but eventually shutsdown Q. Can it be restarted immediately? A. Yes, I can hit the start button and the cycle replicates as many times as I restart-ie runs 40 seconds and shutsdown Q. How is the behavior different than if the STOP button was pressed A. No difference Q. Isn't the fan simply on the AC line so how would its speed change? A. Looks like an AC fan--speeds up only on first cycle--otherwise runs at top speed. Blade turns freely--no obstructions--low ohms on the coil--can sub another fan from a different brand if appropiate--your thoughts Sam--appreciate your help--thanks |
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#4
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"electroninja" wrote in message ups.com... | Ref your questions Sam: | Q. Does it do the same thing if set to defrost.. | A. Yes, will run longer in the cycle but eventually shutsdown | Q. Can it be restarted immediately? | A. Yes, I can hit the start button and the cycle replicates as many | times as I restart-ie runs 40 seconds and shutsdown | Q. How is the behavior different than if the STOP button was pressed | A. No difference | Q. Isn't the fan simply on the AC line so how would its speed change? | A. Looks like an AC fan--speeds up only on first cycle--otherwise runs | at top speed. Blade turns freely--no obstructions--low ohms on the | coil--can sub another fan from a different brand if appropiate--your | thoughts Sounds a bit like an overheat situation. If the fan really is 120V and not speed controlled then I'd be looking for burnt wiring in the AC input system. However, I have a Panasonic doing much the same things. Pulled it apart and found the main MOV across the AC line was shooting flames out of the top! Then I noticed that the main power transistor (this is a inverter machine) has a big crack through the body. Only uWave I ever bought that failed on me. N |
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#5
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NSM wrote: "electroninja" wrote in message ups.com... | Ref your questions Sam: | Q. Does it do the same thing if set to defrost.. | A. Yes, will run longer in the cycle but eventually shutsdown | Q. Can it be restarted immediately? | A. Yes, I can hit the start button and the cycle replicates as many | times as I restart-ie runs 40 seconds and shutsdown | Q. How is the behavior different than if the STOP button was pressed | A. No difference | Q. Isn't the fan simply on the AC line so how would its speed change? | A. Looks like an AC fan--speeds up only on first cycle--otherwise runs | at top speed. Blade turns freely--no obstructions--low ohms on the | coil--can sub another fan from a different brand if appropiate--your | thoughts Sounds a bit like an overheat situation. If the fan really is 120V and not speed controlled then I'd be looking for burnt wiring in the AC input system. However, I have a Panasonic doing much the same things. Pulled it apart and found the main MOV across the AC line was shooting flames out of the top! Then I noticed that the main power transistor (this is a inverter machine) has a big crack through the body. Only uWave I ever bought that failed on me. N |
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#6
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-- No visual evidence of burnt wiring in the system
-- Will monitor fan motor voltage vs speed thru shutdown cycle tomorrow--leaning toward possible fan replacement Thankyou for your input |
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#7
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Sounds a bit like an overheat situation. If the fan really is 120V and not speed controlled then I'd be looking for burnt wiring in the AC input system. However, I have a Panasonic doing much the same things. Pulled it apart and found the main MOV across the AC line was shooting flames out of the top! Then I noticed that the main power transistor (this is a inverter machine) has a big crack through the body. Only uWave I ever bought that failed on me. N First thing I'd check is the fan motor itself, some hair or gunked up grease in the bearings could be making it run slow which overheats the magnetron. |
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#8
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"electroninja" writes:
Ref your questions Sam: Q. Does it do the same thing if set to defrost.. A. Yes, will run longer in the cycle but eventually shutsdown Q. Can it be restarted immediately? A. Yes, I can hit the start button and the cycle replicates as many times as I restart-ie runs 40 seconds and shutsdown Q. How is the behavior different than if the STOP button was pressed A. No difference Q. Isn't the fan simply on the AC line so how would its speed change? A. Looks like an AC fan--speeds up only on first cycle--otherwise runs at top speed. Blade turns freely--no obstructions--low ohms on the coil--can sub another fan from a different brand if appropiate--your thoughts Not sure what you're saying here about the fan. If it runs at top (normal) speed, it's not the problem. The fact that you can restart immediately and get the same exact behavior suggests that it may not be a cooling problem but also check across the thermal protector if possible, or is there a thermistor to monitor magnetron temp? Could be a problem in that area. Is there a schematic with it? --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
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#9
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Ref your questions Sam:
Q. Not sure what your saying here about the fan? A. Fan looks like an AC vs DC fan--one open air coil around core--armature alum--motor has appearance of bathroom vent fan. Fan runs on low speed only on first cycle but speeds up prior to shutdown. Todays test shows 115 volts across motor's coil at both low and high speed. Shaft rotates freely, but will try a drop or two of oil. Q. Is there a thermistor to monitor magnetron temp? Is there a schematic? A. Limited schematic (unit door closed/cook cycle off) One thermal switch on magnetron in series with power fuse--activation shutsdown all power (not our case.) - One oven thermistor shown as input to control unit circuit. No details given (including wire color coding). Had thought this might be convection oven temperature control. - Control unit connected to a "relay unit" --Triac, small transformer, relays etc. Schematic shows one relay that if activated would shutdown magnetron and fan while leaving power to rest of unit (our case possibly.) --Action plan: - Oil fan motor monitor affect - Locate thermistor and test--assume a two wire device whose resistance rises with temp. Uncertain what I should expect for ohm delta--comments appreciated |
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#10
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"electroninja" writes:
Ref your questions Sam: Q. Not sure what your saying here about the fan? A. Fan looks like an AC vs DC fan--one open air coil around core--armature alum--motor has appearance of bathroom vent fan. Fan runs on low speed only on first cycle but speeds up prior to shutdown. Todays test shows 115 volts across motor's coil at both low and high speed. Shaft rotates freely, but will try a drop or two of oil. Q. Is there a thermistor to monitor magnetron temp? Is there a schematic? A. Limited schematic (unit door closed/cook cycle off) One thermal switch on magnetron in series with power fuse--activation shutsdown all power (not our case.) - One oven thermistor shown as input to control unit circuit. No details given (including wire color coding). Had thought this might be convection oven temperature control. - Control unit connected to a "relay unit" --Triac, small transformer, relays etc. Schematic shows one relay that if activated would shutdown magnetron and fan while leaving power to rest of unit (our case possibly.) --Action plan: - Oil fan motor monitor affect - Locate thermistor and test--assume a two wire device whose resistance rises with temp. Uncertain what I should expect for ohm delta--comments appreciated There have been cases where for whatever reason, RFI from the magnetron, triac, who knows, gets into the controller and does strange things. Unfortunately, hard to track down those sorts of problems. But you said it happens on Defrost but takes longer. Defrost is 10 or 20 percent duty cycle (I'm assuming this is your basic HV transformer/cap/diode design) so any heating would be minimal. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
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#11
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On 6 Jan 2005 20:04:23 -0800, "electroninja" wrote:
Sharp Model R1810 Carousel II microwave starts and cooks(heats) but shutsdown after about 40 seconds. Electronic control board display stays lit, countdown stops and displays remaining time--magnetron cooling fan works during the first 40 seconds but then shutsoff--just before shutdown, fan speed increases(doubling or tripling in speed) These items seemed to check out good with VOM-- power fuse interlock switches (2) monitor switch capacitor diode thermal cutout switch(only found one) fan motor power tranformer Additional trouble shooting note--a power surge protector I had plugged the microwave into was discovered fried--suspect a near by lightning strike? Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks Clear the mag first so::Go to the Mag filament wires{ be sure the HV secondary wire is removed} then test for between 2.9vac and 3.9vac depending on model when powered up.Replace Filament wires and re-coneect clipping test leads to mag terminals and check again at switch on for the same a.c. voltage.A lower voltage can be the result of the mag lowering the filament transformer voltage.Move on from there if correct but get the MAG out of the loop first. "Texas Hold'em Poker" "The bigger you bet,the less you win when you lose!" |
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#13
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Located thermistor--results follow:
- Thermistor resistance reading was 275K ohms - Substituted variable resistor in circuit for thermistor and ran system operational testing for multiple values from 16K-2.2Meg ohms --Result: Microwave ran for approximately the same length of time before shutdown (40-60 sec) except for extreme resistance tests ie extreme highs and lows then shutdown was 10-38 seconds. Conclusions: Suspect control board problem--haven't located one from suppliers yet--have have only found a control board varistor replacement part for this unit. Assume a varistor is a variable resistor--part photo from supplier looks like a small capacitor. Comments appreciated regarding possible function of varistor in circuit--are they possibly used in timing control circuits? |
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#14
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"electroninja" wrote in message ups.com... | Located thermistor--results follow: | - Thermistor resistance reading was 275K ohms | - Substituted variable resistor in circuit for thermistor and ran | system operational testing for multiple values from 16K-2.2Meg ohms | | --Result: Microwave ran for approximately the same length of time | before shutdown (40-60 sec) except for extreme resistance tests ie | extreme highs and lows then shutdown was 10-38 seconds. | | Conclusions: Suspect control board problem--haven't located one from | suppliers yet--have have only found a control board varistor | replacement part for this unit. Assume a varistor is a variable | resistor--part photo from supplier looks like a small capacitor. | | Comments appreciated regarding possible function of varistor in | circuit--are they possibly used in timing control circuits? No. They may be voltage variable (varistor) or temperature variable (thermistor, PTC or NTC). Very unlikely that they are used for timing. Is this a sensor model? N |
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#15
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This is a Sharp R1810 convection oven and microwave--it has a sensor
probe if that is what you mean by "sensor model." Trying to figure out what on the control unit might be causing the magnetron to shutdown prior to end of cooking cycle. |
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#16
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On 08 Jan 2005 12:14:31 -0500, Sam Goldwasser wrote:
(Harry Hotspur) writes: On 6 Jan 2005 20:04:23 -0800, "electroninja" wrote: Sharp Model R1810 Carousel II microwave starts and cooks(heats) but shutsdown after about 40 seconds. Electronic control board display stays lit, countdown stops and displays remaining time--magnetron cooling fan works during the first 40 seconds but then shutsoff--just before shutdown, fan speed increases(doubling or tripling in speed) These items seemed to check out good with VOM-- power fuse interlock switches (2) monitor switch capacitor diode thermal cutout switch(only found one) fan motor power tranformer Additional trouble shooting note--a power surge protector I had plugged the microwave into was discovered fried--suspect a near by lightning strike? Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks Clear the mag first so::Go to the Mag filament wires{ be sure the HV secondary wire is removed} then test for between 2.9vac and 3.9vac depending on model Can't overemphasize this. There may be up to 5,000 V at very lethal current availability present on the magnetron filament wires while operating with the high voltage capacitor holding a dangerous charge after shutdown. ANY testing in the microwave oven high voltage circuits is extremely dangerous. Very knowledgeable and experienced professionals have been killed doing this. It's too easy to be careless and you don't get a second shot. If you insist, while unplugged, make sure the HV cap is discharged, then hook up meter, stand clear and turn it on. Take reading without touching meter including its test leads, power down and remove plug from wall socket, discharge HV cap. Etc. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. when powered up.Replace Filament wires and re-coneect clipping test leads to mag terminals and check again at switch on for the same a.c. voltage.A lower voltage can be the result of the mag lowering the filament transformer voltage.Move on from there if correct but get the MAG out of the loop first. Figured after all the tests he had done he would know enough not to test without cap.discharged as he had read your article.Anyway I did say to switch on whilst testing fil.voltage when connected and not connected. I agree with the danger,this is the first road I would go down coupled with mag.filament/case continuity test.Last repair on Sharp I did close to this was the thermal cut out but he said he'd discounted this. Maybe worth another look ranges are 127C to 88C approx for open and reset. "Texas Hold'em Poker" "The bigger you bet,the less you win when you lose!" |
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#17
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Sam--the contoller board has a hardwired LC6041 chip. My spare parts
microwave has the same chip and it works. Ever tried to unsolder a 48 pin LC without damaging it thru overheating? Harry--this unit has only one thermal cutoff switch physically mounted on the casing surrounding the magnetron--electrically it is upstream of all loads and were it to activate it would shutdown everything (lights, fans, control display.. etc)--which is not the case here. Thoughts? Thanks for all comments-- |
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#18
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Update:
--Removed the panel unit (selector buttons, control and relay boards) --Visual inspection shows a zener diode (panel marking Z02) that has overheating signs (black outline around diode.) The zener is 3/16 long, with a diameter of a round toothpick and is much larger than other zeners on the board. Question: Does anyone know a way to determine proper zener replacement visually?(markings, color codes etc.) Plan to replace this diode. Recommendations: Manufacturer no help to this point--authorized factory rep in local area has no listing for the Sharp R1810. Thanks! |
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#19
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On 9 Jan 2005 08:36:24 -0800, "electroninja"
put finger to keyboard and composed: Sam--the contoller board has a hardwired LC6041 chip. Looks like a Sanyo uP. Can't find its datasheet, though. :-( http://service.semic.sanyo.co.jp/semi/search_ds_e.htm My spare parts microwave has the same chip and it works. Ever tried to unsolder a 48 pin LC without damaging it thru overheating? Many times. TV and VCR uPs are of this type. Just use a variable temperature iron and a solder sucker with strong suction, eg a Soldapullt. I re-tin all the pins before starting. Often you can desolder two pins in one go if you bridge them with solder beforehand. Harry--this unit has only one thermal cutoff switch physically mounted on the casing surrounding the magnetron--electrically it is upstream of all loads and were it to activate it would shutdown everything (lights, fans, control display.. etc)--which is not the case here. Thoughts? Thanks for all comments-- - Franc Zabkar -- Please remove one 's' from my address when replying by email. |
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