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Old 03-02-2017, 01:58 PM   #1
cagiva4ever
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Default Microwave oven with burnt Paraller resistors at PCB

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.
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Old 03-02-2017, 02:10 PM   #2
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Default Bosch IXO screwdriver

i have also underwork a faulty Bosch IXO screwdriver. it doesnt have the common fail on it being Switch continuity.

what my IXO seesm to have as a fault is the Power Mosfet regulator, i think.

i have separately tested the Motor and it works fully. also switches etc separately tested an all good. no visible faulty items on PCB or any obviosu signs.

the Mentioned Mosfet seems to be in ShorCircuit mode, its SMD component but in a size that i can de-solder and replace. i just want to be sure before de-soldering it and buying replacement with my small money income, its 100km trip into nearestby component shop.

the Mosfet gets really burning hot, finger burning hot in 10~30seconds, when trigger is pushed pwn control for the motor.


any experienced friendly people here, with tips if this is already a defenitevy sign of a faulty mosfet ?

i.e the signs of shorting mosftet, how they damage and how it appears..


bye
m

ps. i have various underwork projects, and i will post them on this topic as time goes. if i find friendly helpers among Consumer electronics, power tools, Computer equipment etc.


i have diy fixed various equipment during past 15years, i have self educated my self via internet, wihtout any Mentors, so path has been uber long, and mostly in vice versa order in shape of Reverse engineering things how they work.

so i still lack from some basics, as i have no offical education for electronics.
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Old 03-02-2017, 02:33 PM   #3
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Default Re: Microwave oven with burnt Paraller resistors at PCB

Try testing some of the parts that are connected to the resistors with a multimeter and see if you can find any parts that may have gone short circuit because that's probably the reason those resistors burned up.

Also i recommend looking into replacing that relay [at least i think it's a relay] since the side of it was melted by the resistor.
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Last edited by ruky con; 03-02-2017 at 03:07 PM..
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Old 03-02-2017, 02:45 PM   #4
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Default Re: Microwave oven with burnt Paraller resistors at PCB

I cannot download pictures from your Photobucket to look at the boards in details.
The resistors may have burnt up due to the relay is not turned on (or it does turn on but the contacts are bad) to bypass the resistors (you can see how the resistors are connected to the relay contacts), the resistors look to be for softstart circuit.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Old 03-02-2017, 03:29 PM   #5
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Default Re: Microwave oven with burnt Paraller resistors at PCB

hi !

is there summink else that i could do, for you to be able to download them photos ? or is it just your situation location atm that makes it unpossible ?

are you maybe later able with time to download them into your own computer, and have your time in a no horry to look at them ?


i shall start to look for the relay, to source a seller for new1, just in hand source available if needed then later.

yes, the paraller resistors burned the side of the relay. relay didnt seem to have any of its own burning action. resistors only burned its outside surface, not through it, cant thow 100% verify that Relays internals arent now touching relay plastic casing for sure... anyway if relay is faulty this is matterless detail what i just said.

thanks very much for details regarding possible "soft start puspose" . i appriciate very much that kinda details for to Learn.


-"Try testing some of the parts that are connected to the resistors with a multimeter and see if you can find any parts that may have gone short circuit because that's probably the reason those resistors burned up."

PCB has 2 separate circuits in it, which from i have measured other1, as detailled in post #1, diodes.

i might find out new learn new, which is based on if "budm" is later able to see my photobucket PCB photos etc...

bye
m

i have a working good relay on my Benton battery smart charger (car & motobike). iirc it has same values etc pinout as this Oven relay.
Benton has i think cooked Chip in it, but do i dare to take its relay for this purpose. i was hoping to replace the chip for the Benton.

the chip looks like some1 has basically sandpapered its surface, like it has powder on its all surfaces. iirc i have read that it would be 1 of the indication of over temp cooked ic chip(s)

previosly i have only seen visibly Cracked snapped Chips, but never before this kinda...
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Old 03-02-2017, 05:38 PM   #6
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Default Re: Microwave oven with burnt Paraller resistors at PCB

I had a lurk at that link and it worked fine for me, but I had to wait like 20 seconds for the page to pop up. I guess it is slow. I hear ya on living on a stretch, plus recycling something is always fun, money savings and keeping the landfill clean.

As far as these soft start resistors go, they can fail for various reasons. So when they blew up, the microwave should have been dead. Those two resistors act as a inrush current limiter / fuse (soft start). So when the device is turned on, the full current doesn't come in like a bang. I've seen resistors like that blown and usually they fail because something is shorted and there is too much current drawn, low quality, old age, and moisture.
In your case, i'd check that relay if that is still working correctly. I wonder if it arced inside, burnt off the contacts or welded shut. Also check that diode on the secondary (High Voltage side) of the big transformer. Does the display still work?

Last edited by CapLeaker; 03-02-2017 at 06:09 PM..
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Old 03-02-2017, 08:24 PM   #7
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Default Re: Microwave oven with burnt Paraller resistors at PCB

I can see pictures but there is no way to download them to my computer. I store lots of pictures in my photobucket too.
You need to setup to allow people to download pictures, my has 'Download media' icon.
http://s807.photobucket.com/user/budm/library/
The relay contacts should close seconds after the power is applied to bypass the softstart resistors, if they are not bypassed then resistors will burn up., relay contacts are connected in parallel with the resistors for that purpose. You have lots of inruch current with that big power transformer.

Last edited by budm; 03-02-2017 at 08:29 PM..
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Old 03-03-2017, 05:50 AM   #8
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Default Re: Microwave oven with burnt Paraller resistors at PCB

hi !

yes i try to live by appriciating Nature, by all means i can, i pollute as minimal as i can.

i think i have saved 10~20K+ on fixed recycled equipment that i have been given-item swopped and fixed, instead of buying them all new with Retail prices.

the Photobucket.com nowadays is super slow compered to old days, as it now has Adverts up to Spam amount, even "ABP addon at FireFox browser" wont cure it slowness. here in europe Photobucket use to be a "standard" of photo sharing/albums.

iirc i have in purpose of course left it Open to public, free to download, its not a closed Private album. put i shall check it settings today/tomorrow at public Library PC.



the M-oven is only 700Watt's nominal power on datatag. it is oldschool "analog" type, no digital LCD or digital selectors. bought new for my self 6years ago but very little usage, maybe less than 10hours.

always kept dry and clean etc. it is those cheaper Brands modern Chinese production, so to speak.


i shall write more about the Story happening.

i was using the M-oven with half power and only for like under minute, when the Paraller resistors started to smoke. the Cooling Fan is right next to the PCB board, hence the smoke and smell came out Instantly, hence i was able to Shut down the Oven instantly, while still running and smoking the Oven was working fully complitely, no pulsing no flickering, no intermittent anything.

i know that is obviosly not an Sign of "only minor damage" , but it is a promising possibility for only minor damage.



Thanks very much for the indepth details of how the relay works in realtions for them resistors. last night before sleep i was thinking about asking "how it works".

i have serviced cleaned etc some other type of relays in generally speaking, that have been Dismantle able. So latest indepth info wont be forgotten.


i shall open the relay with "dremel" and post of photos, i like to see it my self too.

i shall also measure the diode on the secondary (High Voltage side) of the big transformer.

silly question, but we are talking about the big diode (summink 8~15+amp) at the BIG hv-capacitor, where Diode's Kathode connects into Oven metalbody ground.

iirc i have tested this mentioned diode and it was showing good values, same principals as in them smaller diodes on PCB tested.

but i will measure this HV side diode again, as i have no notes from it saved. i have my Multimeter at mothers home...
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Old 03-03-2017, 06:14 AM   #9
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Default Re: Microwave oven with burnt Paraller resistors at PCB

My bet is a faulty relay being the cause, like I said in my previous post. Replace the resistors and that relay and give it a try.
The story on what happened to the microwave, you should have now a relay that doesn't make make proper contact. Check it out.

Last edited by CapLeaker; 03-03-2017 at 06:16 AM..
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Old 03-03-2017, 06:20 AM   #10
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Default Re: Bosch IXO screwdriver

Quote:
Originally Posted by cagiva4ever View Post
i have also underwork a faulty Bosch IXO screwdriver. it doesnt have the common fail on it being Switch continuity.

what my IXO seesm to have as a fault is the Power Mosfet regulator, i think.

i have separately tested the Motor and it works fully. also switches etc separately tested an all good. no visible faulty items on PCB or any obviosu signs.

the Mentioned Mosfet seems to be in ShorCircuit mode, its SMD component but in a size that i can de-solder and replace. i just want to be sure before de-soldering it and buying replacement with my small money income, its 100km trip into nearestby component shop.

the Mosfet gets really burning hot, finger burning hot in 10~30seconds, when trigger is pushed pwn control for the motor.


any experienced friendly people here, with tips if this is already a defenitevy sign of a faulty mosfet ?

i.e the signs of shorting mosftet, how they damage and how it appears..


bye
m

ps. i have various underwork projects, and i will post them on this topic as time goes. if i find friendly helpers among Consumer electronics, power tools, Computer equipment etc.


i have diy fixed various equipment during past 15years, i have self educated my self via internet, wihtout any Mentors, so path has been uber long, and mostly in vice versa order in shape of Reverse engineering things how they work.

so i still lack from some basics, as i have no offical education for electronics.
To quickly answer this one: You are on the correct path suspecting that FET. I've come across a few where the FET failed. Not on that particular brand, but in general.
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Old 03-03-2017, 07:29 AM   #11
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Default Re: Microwave oven with burnt Paraller resistors at PCB

ive been browsing eBay for them Power Relay's.

this is Relay data on my PCB:
brand: Zanty
model: ztuc-d24hs (apparently 24Vdc ? )
Rating:
10A/250Vac 15A 125Vac
15A/28Vdc 28Vdc


im not accurately familiar with these ratings, if this piticular relay is in Toprange of the Scale or at Minium needed range.

Listing:
24vdc power relay 15A 125VAC
http://www.ebay.com/sch/i.html?_odkw...25VAC&_sacat=0


Matching find per ratings:

http://www.ebay.com/itm/5pc-TTi-TRD-...wAAOxy9MpSPn1q


Question (i could look a datasheet) if i may ask, what is difference on 4-pin relay and 5-pin relay ?

edit: ohh yes i see its for the 2nd Switch
http://www.digikey.com/product-detai...2254-ND/369017

mine is 4-pin.

5th pin at PCB goes into: H(out)
which is not used not i use at this PCB design.



just got a call and a possible free carlift at next week into component shop 100km away trip. i know most parts cost there so much that i cant buy, but i will ask power relay also there, while i buy parts for my O-scopes etc


most likely ebay is my only option to surce the suitable Power relay, so people please feel free to educate me for the Ratings demands.



and Thanks for the latest regarding IXO pwr mosfet. i think i have a replacement item in salvaged part pcb, that is a match that i can use.

back in past when i started to do the IXO, i dint yet have a "magnet solenoid operated heating de-soldering sucker hoover 30W 230vac", which i now have and it works great.

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Old 03-03-2017, 09:26 AM   #12
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Default Re: Microwave oven with burnt Paraller resistors at PCB

Check those safety micro-switches on the door for defects like sticking closed when they should be in open mode. etc.
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Old 03-03-2017, 10:14 AM   #13
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Default Re: Microwave oven with burnt Paraller resistors at PCB

Here are the pictures. It seems that resistor/relay is for changing the power level maybe for a defrost or low power function? If the relay contacts burnt open they won't short the resistor during normal operation so with the constant current through it, it burnt it up.

I found this schematic that shows a similar circuit for the NF series
Here are the relay specs. This panasonic relay JS-B-24V-F (Digikey 255-176-nd) looks similar
Attached Images
File Type: jpg IMG_5946_zpshkaiujph.jpg (134.4 KB, 19 views)
File Type: jpg IMG_5948_zpsr8jbbdlk.jpg (90.0 KB, 9 views)
File Type: jpg IMG_5950__zpsckm9dvww.jpg (85.7 KB, 16 views)
File Type: jpg IMG_5952_zpshnvwmnoy.jpg (74.6 KB, 9 views)
File Type: jpg IMG_5991_zpsbkctwilo.jpg (105.0 KB, 4 views)
File Type: jpg IMG_5993_zpstzodbxmw.jpg (110.7 KB, 4 views)
File Type: jpg IMG_5994_zpsovpovhmh.jpg (99.5 KB, 4 views)
File Type: jpg IMG_5995_zpsjbpwep2h.jpg (118.9 KB, 2 views)
File Type: jpg IMG_5996_zpsbn9hfpmo.jpg (118.9 KB, 5 views)
File Type: jpg Microvawe%20owen%20PCB%20LayOut%20IMG_5952_zpsgqcmh431.jpg (66.7 KB, 6 views)
File Type: bmp MWO Schematic.bmp (407.7 KB, 7 views)
Attached Files
File Type: pdf Zanty Relay.pdf (268.3 KB, 8 views)

Last edited by R_J; 03-03-2017 at 10:57 AM..
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Old 03-03-2017, 04:35 PM   #14
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Default Re: Microwave oven with burnt Paraller resistors at PCB

hi ! ^^thanks for input and them files etc.

door safety switch and 1 other i have tested Prior, and they are working good. i havent measured them with Multimeter but i know that they'r "contact point switches internally work".

i have in past dismantled same type of switches from a MW-oven that i dismantled. and others. so i know how their internals look like and work.

today i checked my MWO spare parts paket. i have a VGC relay at the spares, this 1 exactly, same brand same everything on the box casing written ink:

http://www.remcomplekt.ru/photos/65000/68812.JPG

if i would know understand the Ratings on it VS the original on mine PCB. then if ok good to use this as replacement, i could easyly Run wires from relay and solder them wires into the PCB.

This mentioned linked realy is service/clean dismantle/rebuild able. and made in Korea, way better more robust than them tiny chinese made ones.



and a yet another pulled out project that i maybe post here later: 100watt's inverter. from 12Vdc into 230Vac outlet. but this for way later. just to keep people intrested....Heck lets pull out also electric ChainSaw, new out from pack, only sawed 1 block by ex-owner who gaved it to me free.
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Old 03-03-2017, 09:46 PM   #15
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Default Re: Microwave oven with burnt Paraller resistors at PCB

Did you verify the relay coil resistance to make sure the new one is not going to draw too much current?
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Old 03-04-2017, 11:04 AM   #16
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Default Re: Microwave oven with burnt Paraller resistors at PCB

hi ! ^^

i havent done anything yet to the relay (CHP11-A240S) or with the Relay, ive been waiting to hear what i should do 1st Regarding its suitability.
i have thow opened the relay boxcasing to have a look of its visible condition.

i havent ever before measured any "relay coil resistance", its totally new thing to me. may i ask how to do it ? if its anything special procedure related into it...

at this relay CHP11-A240S
Multimeter into Pin's no#1 and no#2 gives Ohms: 14,53 or 14,71 depending of my 2 Multimeters, when selector @ 20K
those pin's have the "winding symbol" between them.



Today i took loose of the BIG diode from the HV-capacitor/mwo chassy Ground.

its marked:
HVM12
350

is there something special i should know about it, in its construction or is it just a ordinary diode but with big Amps rating.

i measured the diode with both of my 2 Multimeters, and:

i get absolutely nothing for "forward biased Ohms" value.
"Reverse biased" measurement gives/keeps at the .1 for infinity reading value.

Then i measured it with my ESR-meter (this model exact same)

http://www.ebay.co.uk/itm/TS-M8N-Tra...:RRNTB:GB:3160


my ESR-meter basically says: no item attached, unknowm item or faulty item.

the ESR-meter works fully, ive been using it alot on other projects.

so either this diode is faulty broken, or my esr-meter is not upto able to Measure it.



Thanks to "CapLeaker" for pointing out the Diode, if this is it what you ment being the diode. last year i didnt apparently Multimeter it properly, and back then i didnt have esr-meter.



for Bosch IXO i took notes from the "pwr Mosfet" smd-soldered.
it has written on it:
CHN (china?)
D100N
H02L
Y1C429

http://www.datasheetcatalog.com/data...100NH02L.shtml

Last edited by cagiva4ever; 03-04-2017 at 11:24 AM..
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Old 03-04-2017, 11:20 AM   #17
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Default Re: Microwave oven with burnt Paraller resistors at PCB

data sheet for the HVM12 diode
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File Type: pdf hvm5-hvm16.pdf (225.5 KB, 3 views)
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Old 03-04-2017, 11:34 AM   #18
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Default Re: Microwave oven with burnt Paraller resistors at PCB

You can't measure the high voltage diode with a regular meter, it is basically a bunch of diodes in series.
You should be able to short that resistor (relay contacts) and the microwave oven should operate at full power, that way you can make sure the rest of the microwave oven works.
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Old 03-04-2017, 11:44 AM   #19
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Default Re: Microwave oven with burnt Paraller resistors at PCB

EDIT: was given reply above ^^^thanks.


ok, so back to MWO sparepart box tomorrow then. i have there 2 HV-capacitors at the Box and there was 1 HVMxx diode. iirc HV-cap had same Volatge etc on its tag as my Broken MWO has at its HV-cap.

but still, people feelfree to tell if my ESR-meter is not upto the task measuring such High amp and very high voltage Diode, which to me it looks like to be so per its Specs. bare in mind this is new to me, please.



thk god they arent like a 10euros per qty:1 at ebay if needed. but at my nearest Component shop they sure are, and 10e is my food money for 10days.

http://www.ebay.co.uk/sch/i.html?_od...Diode&_sacat=0

Last edited by cagiva4ever; 03-04-2017 at 11:51 AM..
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Old 03-04-2017, 01:00 PM   #20
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Default Re: Microwave oven with burnt Paraller resistors at PCB

i now Multimeter resistance measured the "Burned" power relay while it is IN at pcb.

zener diode and the normal diode "orientation" Block any other component to interefere with measurement, so id say its ok to measure while it is IN at pcb.

only the small capacitor is "actively" in same circuit, conencted inseries.

Multimeter gives readings that jump walk allover, start from ~1300 and go down into zero, flickering....
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