Repairing an oven circuit board

[wopachop]

Hello everyone our oven is throwing an error code. The fix is to send the circuit board in for repairs. I would like to try and fix this myself to save money.

Another guy posted a thread and picture of a repaired circuit board and noted the 2 new capacitors in the upper right corner with the insulated leads and silicone. They are 2.2 and 33uF 50V capacitors. I bought some 100v caps from digiKey and installed them right now but it didnt fix the problem.

Can i manually test the circuit board with a multimeter and determine which components i need to replace? My electronic knowledge is primitive but im eager to learn. Thanks for any help!!

 

[Gryd3]

Inspect the board to see if there is any visible signs of trouble. Discoloration, bulged components, burn marks corrosion. If everything looks good you will need to poke around.

There are 3 basic modes you can use your multimeter in:
Measure Voltage
-This is perhaps the easier method, but could be very dangerous as ovens typically operate at 220V and voltage reading need to be done on a LIVE circuit.
-This will let you poke and prod to determine voltage drops across components and to ensure that the ICs are in fact being supplied the correct voltage.

Measure Resistance
-This will let you measure resistance from one point to another, and will typically only allow you to measure the simpler components (Unless you are familiar with, or have a datasheet for the more complicated components)
-This will REQUIRE that you remove (at least partially) the part you are measuring to ensure that you do not accidentally measure the resistance of a parallel branch that the part may be connected to.
-This is typically done with no power to the circuit making it safer, but also very tedious if you have a large number of parts to check.

Measure Current
-This is a bit of a cross between the two... You need to partially disconnect a part (one part at a time, unless you have more than one meter) and use your meter like a sort of 'jumper' to reconnect that part electrically THROUGH the meter. This again can be dangerous if you are inexperienced due to the voltage present on the board because like the first mode, this needs to be done on a LIVE circuit.

My advice... Take a nice clear picture of the front and the back or 'your' board so we can take a look. Hopefully it jumps out at us.
Otherwise, please send it in. This is not a very good project to learn on in my opinion.

 

[wopachop]

Excellent thank you!! I will remove the board and take some pictures. I did notice burn marks.

 

[Gryd3]

Excellent thank you!! I will remove the board and take some pictures. I did notice burn marks.

You have already removed the board once to replace the capacitors as I understand.
If you are not already aware, please be mindful of those things as they can store a charge for quite some time after you disconnect power. Please always consider your safety when dealing with capacitors, and more so when they are rated at 100V

 

[wopachop]

Thanks i was not aware the capacitor can shock me after disconnecting. I feel dumb for not noticing this earlier. The big blue resistor is loose at the solder pads #183 and 135.

Some of the pics are posting upside down sorry. I rotated and saved them on photobucket but its still wrong.

 

[Gryd3]

I couldn't help but chuckle seeing this XD
If you gave us your very first example picture to troubleshoot I'd be stumped... but these pics show not just one, but 4 at least that I can see right now, parts that have potentially cooked themselves.

Have you gotten a quote yet for a new board or for repairs?

My opinion on this so far, is that you will need to put more work into this to be able to properly follow the traces on the green side of the board. The screen on there is covering a good portion of it. It appears to be soldered on from the top only, but I would advise against lifting it as the leads could break off, and that part does not look cheap. I also noticed that the leads from the display panel are bent, but only near the large TO-220 looking item. (Q2x?) It also appears that this same part was at one point laying on it's back and is now lifted. Was this done by you, and did you notice it making any contact with those bent leads from the display panel?
I would really like to suggest you sending this one in, as it looks as though multiple components are / could be at fault which could make troubleshooting a little more extensive. Many may suggest just swapping in new parts for the ones that are burned / discolored and repairing the solder joint for the large blue resistor you pointed out. This is not always recommended though, as there could be an underlying condition that caused those parts to fails, and putting new ones in may just kill them right away It's that and the fact that this is not a battery operated device that is typically recommended for learning with...

It's your call, but be safe, and this may take up more time than it's worth.

 

[wopachop]

Ive tried to be gentle with the board i think the leads were already bent. Is the TO-220 looking item just to the left of the big blue resistor? That one was standing up it has 3 leads. The one closest to the blue resistor also has a loose solder joint.

Tried to fix it but i think the solder pad might have separated from the circuit board. I soldered it but it popped back off. Its $150 to send in the circuit board for repair. Can they fix the solder pads or is the entire board toast now? Their website says they send it back if they cannot repair it. The part is no longer available from the factory but you can buy refurbished ones for around $250.

edit: forgot to say i tested the resistor and it was 12.3 touching the wire next to the blue body. But when i flipped the circuit board over and tested the other side i got nothing. The resistor has that little black piece coming off of it. Is that broken maybe?

 

[Gryd3]

The TO-220 is the device to the left of the big blue resistor, and seems to me like it was laying down due to the discolouration on the board that appears to line up with where that part would sit if it was laying down.
There are methods to repair circuits where the pad has lifted.
I think the $150 is more than fair if they will still look at it considering it was already 'worked' on. Do you get your $150 back if they cannot fix it?
Perhaps someone else can provide a suggestion?

 

[(*steve*)]

The TO-220 is the device to the left of the big blue resistor, and seems to me like it was laying down due to the discolouration on the board that appears to line up with where that part would sit if it was laying down.

I think it's possibly more likely that whatever is on the board on the opposite side to the discolouration got hot. Maybe too hot.

 

[Gryd3]

I think it's possibly more likely that whatever is on the board on the opposite side to the discolouration got hot. Maybe too hot.

I thought about that. Would be Q27 far right hand of the close-up of the board side above the display, but it had in interesting shape that made me think the TO-220 package was at one point laying down.

Regardless I still think that considering the apparent damages to the board this may not be a project that a beginner should learn with.
You may end up spending the time on the board and needing to buy a new one anyway, and you will be working with dangerous voltages to learn on.

 

[KrisBlueNZ]

What are the markings on the TO-220 device? (The three-lead device standing up.)

What are the markings on the diode (black cylindrical thing with silver or white stripe on it) that's standing up just in front of it?

What is the component that's hidden behind the big resistor?

Can you clean the crustiness off the underside in that area so we can clearly follow the copper traces, and take a zoomed-in picture including the whole discoloured area?

What kind of oven is this from? Brand and model?

Does the error code come up immediately when you power it up? If not, what do you have to do to make it come up?

Does it do anything at all? Or does it just throw the error code and play dead?

Have a good close look all over the board for dry joints and anything suspicious. I wouldn't assume that the problem is necessarily in the area you are focussing on. Discoloration is never a good thing, but it doesn't always indicate a problem.

 

[BruceS]

I have a similar one in a similar condition in a Simpson 2001 oven!! Decided to not even bother repairing it!!

 

[debe]

The slightly scorched parts of the board is not uncommon. But a description of whats not actualy working would be good. One area that is likely to be faulty is relays & connectors associated with switching mains voltage. Check for dry (cracked) solder joints.

 

[wopachop]

Thanks everyone!! Will take pictures and answer the questions asked.

The manual calls the error code a "CANCEL key drive line open"
During a google search i found a post where a guy said the oven door closes and moves a switch. He said the switch sends a pulse signal to the control board. He used technical terms but said this is where the problem exists. But i dont think its the switch, because everyone says to replace the control board and never mentions the switch.

So im hoping i can trace the switch wires to the control board to hopefully find the component thats broken. Trying to find that thread i read but so far no luck.

The oven did start to slightly work since i replaced the 2 capacitors and resoldered the resistor. Even though the resistor is still loose. The oven will now flash the code, i press cancel, and the oven will then run. But after 10 mins the screen goes blank again and the oven does not work.

Makes me think its not completely broken. The goal is to save money and also learn. At this point its mostly to save money.

edit: will take pics in a couple hours to answer the questions