Microwave oven with burnt Paraller resistors at PCB

[cagiva4ever]

Hi !

any friendly Microwave oven experts here ?

i have had this issue underwork now for many months. originally posted on other (useless forum).

Ovens are nowadays cheap, but i have 4-reasons why i will try and fix:
- i try to live Green
- im a diy man i fix all my equipment that i can, i rarely buy anything new, all my equipment are freebys that i have fixed studyed my self.
- money is tight, i have have to choose between new Oven and its value into Food, i will choose the food as i have poverty income.
- i will learn new and i can then in future re-use thse learned Microwaveoven repair skills.




here is copy paste:


Topic issue:

Microwave oven with burnt Paraller resistors at PCB. A circuit at PCB that controls power cut out, Via Door switches qty:2.


Attachments:
a lot of good photos and PCB etc Schematics at my Photobucket at the link pasted, just add in front of the link the usual: http://

s721.photobucket.com/user/Cagiva4ever/library/Consumer%20electronics%20Kitchen%20appliances?sort=3&page=1

this forum wont allow direct links attached, hence above...


-Advice info opinions facts wanted, for if there is a so called “Underlining issue” for a reason why these Paraller resistors have burned out.
i.e if it's a reason because of a possible Over voltage spike at 230Vac household supply
i.e if it's a just because of low grade resistor components
or something else issue such as possible ShortCircuit somewhere.


The Story, what happened:

When the Paraller resistors 5W47ohmJ burned out, I was able to fastly turn of Un-plug the Owen from 230vac in under 5 seconds, as i was standing next to it. While Owen was running it was running functioning normal, no Flickering no pulsing or any other symphtoms.
So I would atm assume that nothing else got broken expect the Paraller resistors, as I cant see any indications burning marks or anything at anywhere else on the Owen circuitry pcb or wiring or Windings externally.


These paraller resistors get a voltage feed directly from 2-stage winding Transformer power supply ,Via Orange wire.

As far as I can see understand looking at the PCB, it has 2 separate circuits in it. I have marked components on to the backside of the PCB for the separate circuit that Consists is made from:

- 1 relay switch
- 1 electrolyte Capacitor
- 1 zener diode
- 1 normal diode
- 2 resistors connected in Series
- 2 resistors connected Paraller 5W47ohmJ , the burned ones. If I understand right, this is the INTAKE side for the orange wire, power supply 2-stage winding supplyes feed into PCB via this T(in) , as the other end is Switch out SW(out)

I haven't yet tested if those Diodes are functioning properly, at least externally they look mint perfect. Afaik burned diode would Cut of the circuitry. And not cause a ShortCircuit to Burn these Paraller resistors or the Relay Ry at PCB.

Also, as the Microwave was running normally while Paraller resistors smoked burned, Id say that 2-stage winding power supply doesn't have any ShortCircuit burn in it.


I have bought new components to replace the Paraller resistors. While buying them, clerk “technician” said to me that thye don't usually burn out in generally speaking regarding such resistors, that there could be Underlining issue causing it.

Im a self educated hobbyist, and I have no degree from electronics, so I don't know all the Basics, which is why I now neep help of a Friendly people.

Fixing this Owen would save me money for 1 month food supply. So I would much appreciate help. Money is tight, my country is living in 7th year in a row economic depression.

Thanks
m





***********************************

somebody replys to me saying:

February 15, 2016, 06:28:50 AM
it is better to test those diodes for possible leak.it is true that burnt diode would cut the circuitry but leaked one is different.try to analyze the circuit further.thanks.

************************************



ok, so i have now Measured both diodes with a good digital Multimeter.

Both diodes give good values, they are obviously NOT short cicruited. Leak test i have not done.

diodes connected into circuit, in their places at PCB "forward biased Ohms" values are:

D1 801Ohms
Zener diode 1.078Kohms

"Reverse biased" measurement gives the .1 for infinity reading value. it doesnt go into 0 zero or act up. with above "forward biased values" this should clarify that circuit isnt jammed OPEN for both direction continuity. Minus leak test.......


any "paraller" interefeence while at pcb, seems higly unlikely having any effect into values/readings on this exact case...


so does anybody have any ideas what could the fault be. Lotsa good photos at my Photobucket all is very visible, the schematics etc etc.