Previous in Forum: Power Engineer Certification   Next in Forum: Different Characteristic PS Class CT for Differential Protection
Close
Close
Close
20 comments
Power-User

Join Date: Jun 2009
Posts: 262
Good Answers: 1

Microwave Oven PCB Bypass

11/15/2012 10:50 AM

The PCB on a microwave oven is not working. What may go wrong if I bypass it and simply put the supply voltage directly (through my timer relay NO contact, and of course, through all the safety switches) simultaneously to the high voltage transformer, the table motor, and the fan motor?

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
Hobbies - DIY Welding - Don't Know What Made The Old Title Attractive... Popular Science - Weaponology - New Member United States - US - Statue of Liberty - 60 Year Member

Join Date: Apr 2009
Location: Yellowstone Valley, in Big Sky Country
Posts: 6954
Good Answers: 282
#1

Re: microwave oven PCB bypass

11/15/2012 11:05 AM

Yeah, I'll bet the PCB is just a dummy, trying to trick you into thinking that a microwave oven needs a moderately complicated control circuit.

What might go wrong? Aside from energetic disassembly and an unscheduled undesired thermal event, I can't think of any real big problem that might occur.

__________________
When you come to a fork in the road, take it. (Yogiism)
Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#2

Re: microwave oven PCB bypass

11/15/2012 11:22 AM

One of the possibilities is a brief firework display, with which one might celebrate Diwali.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Oct 2008
Posts: 42290
Good Answers: 1661
#3

Re: microwave oven PCB bypass

11/15/2012 11:36 AM

You might want to do this outside, or procure a LynDoor™Industries ballistic Kevlar microwave cover if done indoors.

Are there any ac/dc converters on the dead board?

Or, break loose with about 50 bucks and buy a new one.

Register to Reply
Anonymous Poster #1
#4

Re: microwave oven PCB bypass

11/15/2012 12:08 PM

Make a video of your first power on test. You might have the next YouTube viral video.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Oct 2008
Location: Deepest Darkest Rutherford Oz
Posts: 951
Good Answers: 145
#5

Re: microwave oven PCB bypass

11/15/2012 12:36 PM

Here's your sign......

__________________
There are two reasons for a man to do a thing, One that sounds good, and the real one...
Register to Reply Score 1 for Good Answer
Power-User

Join Date: Jun 2009
Posts: 262
Good Answers: 1
#6

Re: microwave oven PCB bypass

11/15/2012 1:27 PM

Why fire ? The thermal cut off will be left there, all other switches too. As I have had little to do with MWO I was afraid the transformer might be receiving some modulated signal from the PCB, but it seems not so: should be just the straight 230 V AC. The oven is not mine: my collegues want to save some money, will not even pay me, just asked to do something possible.

BTW, about the hazards of the MW radiation I am aware.

Register to Reply
Guru
Hobbies - DIY Welding - Don't Know What Made The Old Title Attractive... Popular Science - Weaponology - New Member United States - US - Statue of Liberty - 60 Year Member

Join Date: Apr 2009
Location: Yellowstone Valley, in Big Sky Country
Posts: 6954
Good Answers: 282
#7
In reply to #6

Re: microwave oven PCB bypass

11/15/2012 1:37 PM

Yuri, I have a question for you:

In the competitive world market today, do you believe that a manufacturer places one single component inside of a microwave oven that is not required for safe and proper operation?

Your desire to help out a friend is admirable, why not truly be a good friend to him and tell him "No, it can't be done like that."?

__________________
When you come to a fork in the road, take it. (Yogiism)
Register to Reply
Power-User

Join Date: Oct 2009
Location: Hydro, Oklahoma
Posts: 184
Good Answers: 2
#14
In reply to #7

Re: microwave oven PCB bypass

11/16/2012 8:17 AM

I'm a highly qualified electrician and pride myself in repairing any thing electrically broke and bought and repaired many microwaves. My first lesson came in 1970s seeing a man with half a hand who thought he could repair his..Microwaves are ultra cheap now new and used are givaways. Helping a friend would be buying or getting another one.

__________________
Jim
Register to Reply
Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
Posts: 8778
Good Answers: 376
#9
In reply to #6

Re: microwave oven PCB bypass

11/15/2012 1:43 PM

It isn't worth the risk or the time, especially if you disable any electronic timer function and potentially create a condition where the microwave operates continuously and sets fire to the food. Remember, if there is a problem you will be blamed.

Tell them to get a new microwave, they are dirt cheap now days.

Jack - Used to test microwaves and set fire to food.

__________________
jack of all trades
Register to Reply Score 1 for Good Answer
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8378
Good Answers: 774
#8

Re: Microwave Oven PCB Bypass

11/15/2012 1:37 PM

It shouldn't be much of a problem provided you have a way of turning it off at the right time.

Its just going to run on high output thats all.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Oct 2008
Location: Deepest Darkest Rutherford Oz
Posts: 951
Good Answers: 145
#10

Re: Microwave Oven PCB Bypass

11/15/2012 3:33 PM

For the effort of cludging this piece of equiment so that it may operate in some fashion, it will behove you to kick it to the curb and buy a new one.

Unless you want one with all the bells and whistles they can be had for under $50 from a factory seconds outlet (even less second hand at the pawn brokers). My "private" time is worth more to me than wasting it on afternoon on a stuffed consumer appliance. What about you ? How much is your time worth?

Yes it is noble for you to help your friend, but it isn't really doing them any favours.

__________________
There are two reasons for a man to do a thing, One that sounds good, and the real one...
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15088
Good Answers: 933
#11

Re: Microwave Oven PCB Bypass

11/15/2012 6:19 PM

You're falling for the sucker geek trap here. Your "friend" thinks that you and your knowledge is worthless. They want you to do them a favor by fixing their problem for free while they take your knowledge and you assume all liability. Do not do this! I guarantee that any uneven heating, burnt food, intermittent operation or building fire will be blamed on you. Tell your "friend" that the parts will cost them $50. Your labor charge will be $15 an hour. Your knowledge will cost them $85. You will not offer them any warranty and at home service calls will be $25 an hour not including parts with a $75 minimum.

You clearly have internet access. Show your "friend" this and ask them why they think you are not even worth this.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply Score 1 for Good Answer
4
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4657
Good Answers: 796
#12

Re: Microwave Oven PCB Bypass

11/15/2012 7:55 PM

Assuming that because you are persisting on this folly, you and your friends are so poor that they cannot possibly afford a replacement, here is what the risks are.

As you have likely discovered, the BASIC power components in the microwave oven are a Magnetron (the microwave generator) and a transformer. The power level of the energy going to the transformer (and thereby to the Magnetron) is controlled by a triac. That triac is controlled by the PCB. So as was mentioned, at the most basic level your microwave oven will be permanently on full power because for it to work, you will have to bypass the triac. There are likely at least 3 fuses in the circuit at various points, so the fire risk is relatively low from that standpoint.

But the PCB is more than just a glorified timer and a triac controller, it is also handling much the safety interlocking. So when you bypass all of that, the possibility now exists that there is some unfortunate sequence of events that on some future night of drunkeness, will allow your friends to open the door to retrive their burrito when the Magnetron is emitting full power and not only give them horrific 2nd and 3rd degree skin burns, but also cook their eyeballs from the inside, resulting in permanent irreversible blindness.

If they think they are poor now, just wait.

__________________
** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply Good Answer (Score 4)
Guru
Australia - Member - New Member Engineering Fields - Mechanical Engineering - New Member

Join Date: Sep 2006
Location: NSW Australia
Posts: 1085
Good Answers: 23
#18
In reply to #12

Re: Microwave Oven PCB Bypass

11/17/2012 1:27 AM

He did say it would be rewired through the safety switches as well ,so opening the door will stop the machine just as it would with the pcb in circuit. There is some possibility that the switches could not handle the full current demand so maybe not a good idea.

Also the thermal safety trips would be inoperable as they operate in conjunction with the pcb control.

The machine would operate on full power ok but with the only safety being you with an off/on switch I would seriously ask you not to do this.

__________________
Dont get on to the roundabout if you dont know how to get off
Register to Reply
Power-User

Join Date: Jun 2009
Posts: 262
Good Answers: 1
#19
In reply to #18

Re: Microwave Oven PCB Bypass

11/17/2012 3:36 AM

Thermal safety and the door switches indeed carry the full working current they only do not carry the switching on/off current as prior to switching on/off the button switch turn off a relay on the pcb (whose contact is more robust). I would surely maintain a relay for that end.

The people that asked are not my friends, I can refuse, but it is a matter of priciple.

Register to Reply
Guru

Join Date: Oct 2008
Location: Deepest Darkest Rutherford Oz
Posts: 951
Good Answers: 145
#20
In reply to #19

Re: Microwave Oven PCB Bypass

11/17/2012 7:10 PM

Yuri dear boy, you need to learn the difference between the emotion of ego and matter of principle. Both can be strong and equivalent emotions. The matter of principle really only relates to political, financial endeavours or matters of personal honour. In this case I suspect it is more ego driving the desire to "fix" this microwave than anything else.

As a busted arse radio mechanic, I recognise the symptoms of fix at all (personal) cost to preserve ones status amongst supposed peers. I no longer offer my services to repair domestic appliances even my own (unless its a quick fix). There is no loss of face in refusing to effect a dangerous repair where you wil bear all the responsibility and culpability in having done so. If this was for yourself then yes it's a calculated risk until you could afford to replace it. On a repair for someone else it becomes an insurmountable liability.

Most of the "old hands" here have cautioned you against this primarily because we don't want you to make the same mistake that "we" have done in the past. That is our matter of principle..

__________________
There are two reasons for a man to do a thing, One that sounds good, and the real one...
Register to Reply Score 1 for Good Answer
Power-User

Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 476
Good Answers: 32
#13

Re: Microwave Oven PCB Bypass

11/15/2012 10:22 PM

Never a good deed goes unpunished. On the non-cynical side - DON'T - he/she should still be a friend if you inform them that it's just plain unsafe.

__________________
johny451
Register to Reply
Associate
United States - Member - Old Member

Join Date: Jun 2008
Location: Topeka, Ks.
Posts: 49
Good Answers: 3
#15

Re: Microwave Oven PCB Bypass

11/16/2012 10:02 AM

I have worked on commercial restaurant equipment for 30 years. Also, residential microwaves in some settings. Although commercial microwaves are very much more expensive to purchase & repair, they all work the same at different power levels. That said, I would NOT EVER leave a unit in service that could be used with any function of that piece of equipment not operating properly or bypassed by the user. If they insisted on using the unit while in that state, I would document that before leaving. This is something that is not worth future implications. This is a serious matter, resulting in fire, injury, or death.

P.S. I'm not exagerating!

Register to Reply Score 1 for Good Answer
Power-User

Join Date: Mar 2007
Location: Kansas
Posts: 159
Good Answers: 9
#16

Re: Microwave Oven PCB Bypass

11/16/2012 11:17 AM

You may want to give some consideration for the FCC rules about microwave ovens. If you do not hold the proper certifications, you may be committing a felony or at least a misdemeanor. I am unsure of the laws regarding microwave ovens, but it used to be necessary to hold an FCC license to work on them as the magnetron oscillator operates at high frequency and as such comes under FCC jurisdiction.

You may be able to get away with it, but if you inadvertently bypass some of the interlocks, you could be transmitting rf energy into yourself, your loved ones or into the air where "Uncle Charlie" (FCC) can pick it up and fine you for unauthorized transmission of rf power. (This can get costly and potentially land you in prison.)

Cheers!

Register to Reply
Power-User

Join Date: Nov 2011
Location: New Hampshire
Posts: 406
Good Answers: 3
#17

Re: Microwave Oven PCB Bypass

11/16/2012 11:34 AM

How to bypass PCB in microwave:

A. Shift appropriate wires to new location

1, Talk to insurance company about personal injury,

2, Talk to home insurance company about cellar hole where house used to be

3. Talk to cell mate about rules for cell.

Register to Reply
Register to Reply 20 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (1); Doorman (2); garth (1); jack of all trades (1); Johny451 (1); JRaef (1); jtd405 (1); lyn (1); Munster (1); PWSlack (1); redfred (1); RG2 (1); Sasnak (1); tcmtech (1); Tobugrynbak (3); Yuri B. (2)

Previous in Forum: Power Engineer Certification   Next in Forum: Different Characteristic PS Class CT for Differential Protection

Advertisement