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Whirlpool Oven/Microwave board repair

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surfref32

New Member
Hi, I'm Andy from SC. I know very little about electronics and I have a question. The resistor in the pic is open. Can anyone tell me the wattage and resistance? Thank you.
 

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ke5frf

New Member
BTW, buy several of them if you are attempting a repair yourself. Chances are you have another problem that is causing a short and burnt the resistor by overcurrent. Is that diode the magnetron diode? Is the resistor part of the magnetron circuit? I would be concerned with the voltage doubler circuit which includes a capacitor having a shorted component. If you are going anywhere near this stuff, please be careful and discharge the capacitor with insulated tools.
 

surfref32

New Member
are you sure about the resistance? The info I have says the three bands that are together are the value and the one spaced away is the tolerance? I'm not saying you're wrong, just checking. I don't want to fry this thing. Thanks, Andy
 

ke5frf

New Member
are you sure about the resistance? The info I have says the three bands that are together are the value and the one spaced away is the tolerance? I'm not saying you're wrong, just checking. I don't want to fry this thing. Thanks, Andy
Actually, no I'm not sure.
First mistake I made was using an online calculator and plugging in the colors instead of doing the calculation myself. I didn't notice that an error message popped up because the colors I entered were an invalid combination. The default value on the calculator is what I offered earlier by mistake. It fooled me. I didn't even check. My apologies.

However, the 1st stripe in a 4 band resistor cannot be silver or gold. So, the resistor has to be read, on your photo, from right to left.

But, this is why it is important for you to verify the colors. I am seeing black, red, white, gold. This combination is invalid. white is 10 to the 9th power in that case. No way.

Please look closely and tell us what the colors are, in order. If the picture is not picking up another stripe, please detail it.

Again, my apologies for not catching my lazy mistake.
 

ke5frf

New Member
After taking the time to actually consider this instead of going on autopilot, I believe this is not a resistor. It is an inductor.

The first band must be grey. Is it not? It appeared silver or gold to me on my monitor.
This is the only way it makes sense, because if this were a resistor, the last band of a 4 band resistor can't be black. But black indicates +/-20% tolerance for an inductor, so it is valid.

Grey,white,red indicates 8.9 millihenries.

If this is the color combination you see, unless I am blind or crazy this must be correct.
I would not want to venture a guess about the power rating.
 

surfref32

New Member
I had the same trouble with the colors and my eyes see the same things your's do. The board is marked R175 in that spot and I can only guess that means resistor number 175 on the board. The colors didn't make sense to me either. This thing got very hot as you can see so I can only assume that the heat changed the colors a bit from what they were originally. This is where experience comes in and that's something I don't have. The factory schematic would be nice but I have no clue where to find it. The board is a Whirlpool #4448877. There's a pic of a new one online but the resolution isn't good enough for me to ID the resistor.

Even though we haven't come to a conclusion yet, I want you to know that I appreciate you taking the time to check on this for me.

Edit, I hope this pic is a little better.
 

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Mad doggy

New Member
That 1st band

Hi, the first colour band might have been brown . That will give you brown ,white , red ( 1.9 kΩ ). Not sure about the last band as a black does not add up for a resistor. What I do in a situation like this is to use a sharpie or file and file the resistor open. Then use my multimeter on the carbon track to try and make out what the resistance should be.
 

HiTech

Well-Known Member
That is definitely a resistor and further supported by the fact that the PCB indicates it as R175. The band on the far end may be the TEMP Coefficient band as list in this chart:
 

ke5frf

New Member
I hadn't even noticed that the resistor had a board label. Panning the picture out helped.

So, it has to be a resistor, but the colors don't make sense to me. Very confusing.

HiTech. I'm definately not arguing that this is a resistor for obvious reasons. But how what would you judge the value to be based on the "Violet Gives Willingly" rhyme? i.e the chart.
 

ke5frf

New Member
This is challenging me :)

I Googled the board number you gave, and evidently it is a clock control board for an Oven/microwave combo. #4453168 is an available replacement part number on some sites according to my Googling.

Judging by some low resolution photographs of the 4453168 board, this circuit is heavily populated with resistors.

So here is what I would do if I had the board in front of me. I would look to find another resistor with the exact same color code and determine its value with my ohm meter. I would desolder it from the board, at least one leg, to verify the value. I would match it with the highest power rated, lowest tolerance resistor of the same ohmic value I could find.

If no exact component exists on the board elsewhere, I would make a chart of all the color code combinations of all the other existing resistors. I would then proceed to read them with the meter, desoldering one leg on each resistor. I would pay special attention to resistors with one or more of the same color stripes. I would deduce the value of the resistor based on the process of elimination so to speak. That is to say, I would do this if the pattern turned out to be non-standardized. If I noticed the pattern on the other resistors mirrored the standard, I wouldn't waste my time going further.

With luck, you'll be able to figure the value out with just a few logistic measurements. If you follow this method, let us know what you find.
 
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HiTech

Well-Known Member
It's likely 1900Ω or 1.9KΩ and don't worry about that last band.... whether it's tolerance or temperature. It's not precision electronics for a µwave oven. If anything clean all that carbon charring off the board before soldering in a replacement.
 

ke5frf

New Member
I wouldn't make assumptions. I would make every effort to deduce the value of the resistor, even if it meant going to an appliance store and kindly asking an experienced repair person if they are familiar with this fault. Chances are, this is common. In fact, Googling R175 and Whirlpool led me to an appliance forum with someone looking for the same information.

It would be nice to have a little more background. Model# of the appliance, and a little reverse engineering (i.e. trace the components that surround the resistor and are electrically connected to it. One concern is that the faulty resistor is not simply THE fault, but rather a symptom of it. Taking the time to investigate the circuit further might offer valuable clues. Perhaps another photo of a larger block of the circuit board might be worthwhile, front and back planes. That is, if you haven't already given up :)
 

surfref32

New Member
OK here's the story... I bought this appliance new 13 years ago. It's in very nice shape and I like it. Last weekend the microwave died. You could still use the pad to enter in a time but the time would just clear when you hit start. The interior light was also inoperative. I called on Mon and found the board is NLA but found a company would fix my old board. Problem was that once I send the board off, I have no microwave or oven and with family coming for Christmas the timing of shipping the board out, getting it fixed and back was going to be tight. If they had it longer than the 7-10 days they quoted, I'd have to buy a new one and I'd be out of the money to repair it since they charge you before they fix it. I had little confidence that they would be on time so I started shopping for a new oven/microwave. The best I could find was $1,700, not a small chunk of change. As a last minute thing before I pulled the trigger, I figured I had very little to lose if I tried to repair it. I took a guess that the heat changed the colors and that I needed a 1.9K ohm resistor. I hopped in my van and went to Radio Shack. They had nothing close but I was able to get two 1K ohm 1 watt resistors for $1.49. I installed them in series to get 2K ohms, which is a little over 5% more than 1.9k ohms. I didn't have a lot of faith, realizing that most likely something caused the resistor to burn, and also I wasn't sure about the value. There was also a blown 20A fuse that I replaced. Well, it's been working perfectly all week and we use it a lot. I posted here because I don't know what I'm doing and since the whole thing hasn't gone up in smoke yet, I figured I still had a chance to get the right resistor and install it. I searched and had no luck even finding a 1.9k ohm resistor and that worried me too. Now that you know the rest of the story, what do the experts think I should do now?
 
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HiTech

Well-Known Member
Two 1kΩ resistors connected in series is close enough to 1900Ω, especially if that resistor is of 20% tolerance... that + 380Ω either high or low of 1900Ω. Once again this isn't medical life support equipment. Microwave control boards use some specific parts on them but often their design is tolerant of general replacement parts. If it's working, keep an eye on it and go from there. Don't make life harder for yourself any more than necessary. Just be damn careful when dealing around the magnetron and other high pot parts or you could die!
 

ke5frf

New Member
I think you are on the right track and have learned a lot already.
I am impressed with your deductive logic. I would presume the 2K resistance is close enough, given the assumed 1.9K value. I am a little more cautious than HiTech though, because it is microwaves we're talking about, though the safety interlocks on the doors are there for a reason.

And if nothing else, it is a learning opportunity.

I'm thinking the resistor we're discussing here is involved in the magnetron TRIAC or relay control circuit as well as the cavity light. There will be transistors in most circuits driving 1)a relay for the blower motor, cavity light and 2)a relay or an optical isolator with an internal diac that gates the TRIAC for the high voltage transformer/magnetron. There has to be independant switching because the cavity light can come on with the door open OR when the start cycle has triggered it and the magnetron.

We can assume the CPU power supply is working because the control panel and clock are working.

So somewhere between the microprocessor and the relay/triac for the lights, motors, and magnetron this resistor is involved in the switching function. Obviously, it is working and likely the value you chose is correct. Depending on the resistor function, it sometimes is OK for a higher value as a replacement. It is when your substitution is too low that you run into trouble.

Given your symptoms, I think you are fine just going with it. You should be fuse protected anyway so if something were to fail again hopefully the fuse will do its job.
 

surfref32

New Member
Thank you so much ke5frf and HiTech. I feel better now. I realize I got very lucky with this whole thing. If the board was still available I would've just spent the $300+ on a new one. I fix everything in the house, be it plumbing, electrical, carpentry HVAC and I do all my own automotive work and have for the 16 years I've been married. I was an auto mechanic and now have been a HVACR mechanic for 20 years. I draw the line when it comes to repairing electronic control boards, I only replace them. Because of all that, my wife expects me to do all this and is very hard to impress but this impressed her. lol.

Merry Christmas!!
 

mizzle

New Member
DUDE.

I literally had the exact same problem with the oven/microwave combo at my parents' place about two years ago.

I also followed your logic stream and decided to solder some resistors together and hope for the best (I went even more ghetto, as my Radioshack was especially terrible and had like 12 resistors in the entire store, so I soldered 4 together in series to get about 2k ohms). As was the case with you, the thing worked again and worked very well until a week ago so I've been tasked with fixing it again. This time, the resistors I used were completely burned up so in my searches to find more information about the control board, I stumbled upon your thread and AWESOME pictures. So instead of buying a new multimeter tomorrow, I'm just gonna go out and grab some more resistors :D

Hope your repair is still holding up!
 

surfref32

New Member
Glad the thread helped Mizzle. The microwave is still doing it's job daily and now my kids are older so they're using it too. Please update this thread with your results.

Last Christmas I got nervous about it breaking again and tried to find a used board I could send out to be redone but had no luck at all finding one. If anyone reads this and has a board they would like to sell post it here.

Thanks,
Andy
 
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