• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake
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Samsung NQ70M7770DS/AA Microwave Oven Wall Combo - Microwave works but no heat

zdmservices

Premium Member
Joined
Jun 18, 2022
Messages
2
Location
Portland OR
Model Number
NQ70M7770DS/AA
Brand
Samsung
Age
1-5 years
Hello! I have been troubleshooting this for months off and on and am at a standstill at this point. It all started with a C-A2 code which ended up being a burnt up power relay on the PCB. Samsung tech replaced the wiring harness, PCB, and right door latch/switches to no avail. After a third visit, Samsung basically said there is nothing they can do. At this point I've done the following:

-Replaced both PCBs and checked all the relays for functionality
-Replaced the wiring harness again
-Replaced the latch and all switches on the right side
-New magnetron and diode as well as magnetron TCO
-New upper and lower fans
-New thermistor for MWO (although it appears to be faulty)
-Confirmed functionality of all TCOs
-Confirmed functionality of transformer and capacitor
-All switches tested for functionality
-Tested several wires in the harness end to end to rule out shorts/continuity issues

The oven fully functions. However, the microwave will run on all settings (micro, convection, broil, etc) but will never produce any heat. Also, when the door is opened the magnetron cooling fan turns on but immediately shuts off when the door is closed. I also discovered that the thermistor for the MWO was testing at over 200k ohms but the service manual says it should read 1,080ohms. The replacement one (pulled from a scratch and dent) is also reading this so I'm wondering if it is defective or if I am doing something wrong. Sometimes the screen will read a C-20 error code which pertains to this sensor and the lower oven sensor. The lower oven sensor reads 1,080ohms which reinforces the idea that perhaps the other thermistor is bad. Looking at the schematic, it isn't clear if that is enough to trigger some sort of failsafe for the MWO. One would think this $4,500 unit would be smart enough to thoroughly diagnose itself but I guess that's asking too much.

Any help or insight at all would be greatly appreciated!
 

actechrep

Member
Joined
Nov 30, 2022
Messages
1
Location
Florida
Hello! I have been troubleshooting this for months off and on and am at a standstill at this point. It all started with a C-A2 code which ended up being a burnt up power relay on the PCB. Samsung tech replaced the wiring harness, PCB, and right door latch/switches to no avail. After a third visit, Samsung basically said there is nothing they can do. At this point I've done the following:

-Replaced both PCBs and checked all the relays for functionality
-Replaced the wiring harness again
-Replaced the latch and all switches on the right side
-New magnetron and diode as well as magnetron TCO
-New upper and lower fans
-New thermistor for MWO (although it appears to be faulty)
-Confirmed functionality of all TCOs
-Confirmed functionality of transformer and capacitor
-All switches tested for functionality
-Tested several wires in the harness end to end to rule out shorts/continuity issues

The oven fully functions. However, the microwave will run on all settings (micro, convection, broil, etc) but will never produce any heat. Also, when the door is opened the magnetron cooling fan turns on but immediately shuts off when the door is closed. I also discovered that the thermistor for the MWO was testing at over 200k ohms but the service manual says it should read 1,080ohms. The replacement one (pulled from a scratch and dent) is also reading this so I'm wondering if it is defective or if I am doing something wrong. Sometimes the screen will read a C-20 error code which pertains to this sensor and the lower oven sensor. The lower oven sensor reads 1,080ohms which reinforces the idea that perhaps the other thermistor is bad. Looking at the schematic, it isn't clear if that is enough to trigger some sort of failsafe for the MWO. One would think this $4,500 unit would be smart enough to thoroughly diagnose itself but I guess that's asking too much.

Any help or insight at all would be greatly appreciated!
Good afternoon, did you fix the Samsung combo oven?
 

zdmservices

Premium Member
Joined
Jun 18, 2022
Messages
2
Location
Portland OR
Good afternoon, did you fix the Samsung combo oven?
Unfortunately, it was never resolved even after having been looked at by a high level robot tech and a couple engineer friends. Samsung should be absolutely ashamed that something of this nature effectively isn't repairable.

On the bright side, I played Samsung's game and eventually managed to get a replacement unit at no cost. ;)

I do still have the original unit and would one day still like to figure out how to fix it. Since the PCBs, harness, and all of the power related components have been replaced, it really is a mystery as to where to take it from here. So if anyone stubbles across this forum and knows where to start, let me know!
 
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