Microwave oven - troubleshooting fault finding and repair

First i test the mains cable from the pin on the plug to the terminal on the incoming mains PCB board inside the microwave, first set multimeter to read ohms continuity and you should get very low ohms reading if you OL you have  faulty cable or fuse has blown is either plug or internal to microwave. 

Actually first thing is to discharge capacitor to void injury

 

Short out the terminals of the capacitor with an insulated set of pliers.

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Here i test the live both sides of internal fuse so i am testing the fuse as well 

and then do the same on the neutral pin to neutral terminal on PCB board

if you get 

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Below i am testing the thermal cut out its easy to get to and easy to do so my as well do it now 

Below i am testing the bulb this is 141.6 ohm so very good 

not an essential test but easy to do and again easy to get to 

Now ill test the door micro switches there are three of them and they provide 

protection preventing the microwave operating when door is open and any 

risk of exposure from the waves , so very important these work correctly s 

they can turn off power to the primary side of winding preventing it working

as you can see with door closed the switch is on and low continuity

with the door open the switch turns off and meter should red OL 

beware some switches may be the opposite and turn open when open 

Test ll three micro switches and ensure the same results are seen

closed

                                                                               open

last one with the door closed we have  reading on multimeter 

close up of connections to microswitch 

and door open the switch is open and multimeter shows OL 

Now i test the primary winding side of the transformer 

Primary winding was 3.4 ohms so good if it was short circuited or 

OL it would be faulty.

Next i check the high voltage output side tap of transformer you test for the terminal 

pin to ground and usually read from about 90-180 ohms and should not be short circuited 

This one reads 75.8 OHMS so happy with that 

next i test the secondary winding of transformer it can take some tracing which wire is 

which but you should find them , trace them back to the transformer and test this one reds 

1.3 ohms and is not short circuited or leaking to earth so good 

Next i switch meter to capacitance mode to test the capacitor and test across the 

DISCHARGED capacitor it reads just under  micro farad check side of capacitor to

see actual size to compare

Next i test the diode i cannot get  reading in both diode mode or high ohms 

im suspecting it might be a fail but you need to do further testing in order 

to be certain.

see video here for testing these 

as you can see i tested in both direction instead of swapping 

the clip around i just swapped leads in meter as its easier but just ensure you test both ways 

see video link to see a good reading 

if the primary side or transformer is not getting power it could be either 

micro switches or this rely on the main control board and is bout the only repair that can be done on board before needing to replace the PCB

See video of this process below