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Hv diode no power to display

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Please post a new help request here on FixYa and include the full model number from the tag in the cooking cavity or elsewhere on the microwave, such as the door frame, controller frame, etc. and detailed symptoms and when they occur.

Posted on May 04, 2013

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Posted on Jan 02, 2017

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Can a microwave be repaired?


Yes it is repairable, but if you do not have any experience in the repair of microwave ovens do not engage in their repairs because it is one of the most dangerous household appliances and the consequences can be disastrous. If light and turntable works than low voltage circuit (220V or 110V) works well. In this case the problem is in a high voltage (HV) circuit which is made up of the magnetron, HV diode (rectifier), HV capacitor and HV fuse or protect diode. Failure is in any of these components in "HV circuit" or in the main board. If light and turntable does not work than fault could be in power supply elements like: power supply cord, transformer, power board, fuse (glass or ceramic, ussualy 8A, 10A or 12A) on power board.

Dado

Oct 24, 2015 | Kenmore Microwave Ovens

Tip

Troubleshooting Guide


  • Problem: Totally dead oven.
    Possible causes:
    1. No power to outlet (blown fuse or tripped breaker or GFCI).
    2. Blown main fuse - likely due to other problems.
    3. Open thermal protector or thermal fuse.
    4. Defective controller or its power supply.
    5. Clock needs to be set before other functions will operate (some models).

  • Problem: Totally dead oven after repair.
    Possible causes:
    1. Cabinet screws replaced in incorrect location (safety interlock not engaged).
    2. Any number of screwups. :)

  • Problem: No response to any buttons on touchpad.
    Possible causes:
    1. Door is not closed (some models).
    2. You waited to long (open and close door to wake it up).
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Defective interlock switches.
    5. Faulty controller or its power supply.
    6. Touchpad or controller board contaminated by overenthusiastic cleaning.
    7. Defective/damaged touchpad.

  • Problem: Oven runs when door is still open.
    Possible causes:
    1. Damaged interlock assembly.
    2. Cooling fans (only) running due to bad sensor or still warm.

  • Problem: Oven starts on its own as soon as door is closed.
    Possible causes:
    1. Defective triac or relay.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.

  • Problem: Oven works but display is blank.
    Possible causes:
    1. Defective controller or its power supply.
    2. Broken display panel.
    3. Oven needs to be reset (pull plug for a minute or two to reset).

  • Problem: Whacked out controller or incorrect operation.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.
    6. Defective sensor (particulalry covection/mirowave combos).

  • Problem: Erratic behavior.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Bad connections in controller or microwave generator.
    3. Faulty relay - primary (or HV side, much less commonly used).
    4. Defective controller or its power supply.
    5. Bad contacts/connections on mechanical timers. Intermittent fuse.
    6. Power surge at start of cook cycle confusing controller.
    7. Microwave (RF) leakage into electronics bay.

  • Problem: Some keys on the touchpad do not function or perform the wrong action.
    Possible causes:
    1. Touchpad or controller board contaminated by overenthusiastic cleaning.
    2. Defective/damaged touchpad.
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Faulty controller.

  • Problem: Microwave oven does not respond to START button.
    Possible causes:
    1. Defective START button.
    2. Faulty interlock switches.
    3. Door is not securely closed.
    4. Faulty controller.
    5. You waited too long - open and close door to wake it up!

  • Problem: No heat but otherwise normal operation.
    Possible causes:
    1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
    2. Bad connections (particularly to magnetron filament).
    3. Open thermal protector or thermal fuse.
    4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
    5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
    6. Defective HV relay (not commonly used).

  • Problem: Timer and light work but no heat, cooling fan, or turntable rotation.
    Possible causes:
    1. Defective (lower) door interlock switch or door not closing fully.
    2. Faulty relay or triac.

  • Problem: Fuse blows when closing or opening door:
    Possible causes:
    1. Defective door interlock switch(s).
    2. Interlock switch knocked out of position.
    3. Misaligned door.

  • Problem: Loud hum and/or burning smell when attempting to cook.
    Possible causes:
    1. Shorted HV diode, magnetron.
    2. Burnt carbonized food in or above oven chamber.
    3. Shorted winding in HV transformer.
    4. Frayed insulation on HV wiring.

  • Problem: Arcing in or above oven chamber.
    Possible causes:
    1. Burnt carbonized food deposits.
    2. Exposed sharp metal edges.

  • Problem: Fuse blows when initiating cook cycle.
    Possible causes:
    1. Defective interlock switches or misaligned door.
    2. Shorted HV capacitor.
    3. Shorted HV diode.
    4. Shorted magnetron (probably won't blow main fuse but HV fuse if used).
    5. Defective triac.
    6. Old age or power surges.
    7. Defective HV transformer.
    8. Short in wiring due to vibration or poor manufacturing.

  • Problem: Fuse blows when microwave shuts off (during or at end of cook cycle).
    Possible causes:
    1. Defective triac (doesn't turn off properly).
    2. Defective relay.
    3. Shorting wires.

  • Problem: Oven heats on high setting regardless of power setting.
    Possible causes:
    1. Faulty primary relay or triac or HV relay (not commonly used).
    2. Faulty controller.

  • Problem: Oven immediately starts to cook when door is closed.
    Possible causes:
    1. Shorted relay or triac.
    2. Faulty controller.

  • Problem: Oven heats but power seems low or erratic.
    Possible causes:
    1. Low line voltage.
    2. Magnetron with low emission.
    3. Faulty controller or set for wrong mode.
    4. Stirrer (or turntable) not working.
    5. Intermittent connections to magnetron filament or elsewhere.
    6. Faulty primary relay or triac or HV relay (not commonly used).

  • Problem: Oven heats but shuts off randomly.
    Possible causes:
    1. Overheating due to blocked air vents or inoperative cooling fan.
    2. Overheating due to bad magnetron.
    3. Bad connections in controller or microwave generator.
    4. Faulty interlock switch or marginal door alignment.
    5. Faulty controller.
    6. Overheating due to extremely high line voltage.
    7. Stuck stirrer fan resulting hot spots detected by sensors.

  • Problem: Oven makes (possibly erratic) buzzing noise when heating.
    Possible causes:
    1. Fan blades hitting support or shroud.
    2. Vibrating sheet metal.
    3. Vibrating transformer laminations.
    4. Turntable or stirrer hitting some debris.

  • Problem: Oven light does not work.
    Possible causes:
    1. Burnt out bulb :-).
    2. Bad connections.

  • Problem: Fans or turntables that do not work.
    Possible causes:
    1. Gummed up lubrication or bad motor bearing(s).
    2. Loose or broken belt.
    3. Bad motor.
    4. Bad thermostat.
    5. Bad connections.

on Mar 30, 2008 | Kenmore 80412 Microwave Oven

1 Answer

My 5 yr old Whirlpool microwave stopped heating food. All other lights, displays, fan and turntable work. What could be the trouble?


If you do not have any experience in the repair of microwave ovens do not engage in their repairs because it is one of the most dangerous household appliances and the consequences can be disastrous. According to your description, low voltage circuit (220V or 110V) works well (light, turntable...). Obviously the problem is in a high voltage (HV) circuit which is made up of the magnetron, HV diode (rectifier), HV capacitor and HV fuse or protect diode. Failure is in any of these components in "HV circuit" or in the main board.

Dado

Jun 09, 2015 | Whirlpool Microwave Ovens

1 Answer

Whirlpool microwave keeps opening high voltage diode


If you do not have any experience in the repair of microwave ovens do not engage in their repairs because it is one of the most dangerous household appliances and the consequences can be disastrous. According to your description, low voltage circuit (220V or 110V) works well (light, turntable...). Obviously the problem is in a high voltage (HV) circuit which is made up of the magnetron, HV diode (rectifier), HV capacitor and HV fuse or protect diode. Failure is in any of these components in "HV circuit" or sometimes in interlock switch assembly or PC Board.

First, you must be sure which diode is blowed, reactifier or protect diode.

To check magnetron following this procedure:

Discconect the mains supply.
Check that the capacitor is discharged (by resistor 100 ohm / 10W or more).
Discconect the magnetron.
Measure the resistence between the disconnected terminals (should be app. 0.5 ohm).
Measure the resistance between the supply terminals (both) and earth. The resistance should be infinite.

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Dado

Mar 12, 2015 | Whirlpool MT4155SPS

1 Answer

Can anyone please advise on Lamona combi HSA7020 which will not work as a microwave despite all the display looking as if it will heat up but then it doesn't?


mw not working is either the magnetron or the diodes in the HV power supply.

If u r brave and want to fix it start with the diodes as they r a lot cheaper than the magnetron. Otherwise, take it to the dump.

Dec 09, 2014 | Microwave Ovens

1 Answer

Electrolux combi integral microwave EMS26414W does not microwave/defrost.The display/turntable/light/grill does work


Failure should be found in the high voltage section of microwave oven.
Magnetron, HV capacitor, HV diode or HV fuse, tranformer HV secondary coil

Dado

May 27, 2014 | Electrolux Microwave Ovens

1 Answer

Mcc 3880e m


There is no microwave, so I suggest to check all HV components (magnetron, HV reactifier diode, HV fuse or protect diode, HV capacitor and eventually transformer).

Dado

Jan 22, 2014 | AEG Microwave Ovens

1 Answer

Why would the high voltage capacitor go bad?


Hi and welcome to FixYa. I am Kelly. High voltage capacitors can and do fail when a microwave is used for long periods of operation, when the unit is operated with no internal load and sometimes for no reason at all other than the capacitor had an internal failure such as corrosion or a break down of the metal strips inside of it where the strips can make contact with the the case. I have been working on microwaves since the 70's and often there is no apparent reason for the failure of the HV cap.. They just sometimes fail.
However...... there is also a power diode in the microwave that is connected directly to one terminal of the HV Cap. If the power diode has failed it can cause subsequent failure of the HV Cap. The Sharp Power diodes can be found here: http://www.repairclinic.com/Sharp-Microwave-Parts?s=t-FH-DZA119WRKZ-%3d%3db113a6c41

You use and ohm meter on resistance to check the diode AFTER removing the terminal of the diode from the capacitor. NOTE: the capacitor must be shorted across the terminals at least 3 times with a screwdriver while holding the handle only to prevent a horrible shock.
Once the diode terminal is disconnected from the HV Cap read resistance in BOTH directions by reversing the test leads on the terminals of the diode. One direction will read resistance and the other direction it will read open / infinity. Any other reading is a failed diode.

You check the capacitor using an analog (scaled vs digital display) ohm meter on R X 1,000 or R X 10,000 and watch for a jump on the meter just as you touch the terminals EACH time you reverse the leads. No jump or... steady resistance = bad Cap.

Sharp Capacitors can be found here:
http://www.repairclinic.com/Sharp-Microwave-Parts?s=t-FH-DZA119WRKZ-%3d%3db113a6c12

Just note that either a CAP or Diode failure can cause the main fuse to blow at the end of the power cord in the fuse holder.

Fuses are normally either 15 or 20 A Slo-Blo fuses and can be found here:
http://www.repairclinic.com/Sharp-Microwave-Parts?s=t-FH-DZA119WRKZ-%3d%3db113a6c44

Thanks for choosing FixYa

Kelly

Sep 29, 2010 | Sharp Dial Microwave R-21LCF Microwave...

1 Answer

Hi, I have a SHARP Microwave Model R398F. Its less than a year old. The display and timer work fine but does not heat up. Can you please let me know what the problem could be. Thanks Js


If the operation is otherwise normal with the exception of heating food, common causes include; (to diagnose requires discharging of the HV capacitor) if you are inexperienced with working with HV I suggest seeking professional help.

Open thermal protectors or thermal fuses.

Open HV Diode.

Open HV capacitor

Open magnetron filament

Open winding in HV transformer

Defective HV relay

Shorted HV diode

Short or other fault in the magnetron

Short in certain portions of the HV wiring

Replacement Magnetrons (the most likely cause if not charring or defective components are found when troublshooting the small parts, can typically be had for around $45.00 just do a web search for your model number.

Good Luck

Sep 07, 2010 | Sharp Microwave Ovens

1 Answer

Kitchenaid KCMS185JSS-3 microwave - no power


Well your gonna have to take it down a take apart the microwave more than likely. Probably have a shorted HV diode,magnetron, shorted winding in HV transformer.burnt or frayed HV wire insulation

Sep 03, 2009 | KitchenAid KCMS185J Microwave Oven

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