PCB repair to a Whirlpool Double Oven control board

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
This Whirlpool Double Oven model RBD305PDB12 would have a black screen and not work intermittently. It would stop working for months and then would come back on its own and work for anywhere from a few days to weeks only to go back to a black screen and not work.

Upon removal of the control board there is a blown area where there used to be a ceramic capacitor as part of the a/c to d/c bridge rectifier as shown below:
https://drive.google.com/file/d/1pqPHS9IiFLdxxlQQ1EC7C6CX6p_Ue8Yz/view?usp=sharing

The diode that connected to the blown ceramic capacitor was removed and upon removal the pad on the pcb for the diode came off. This pad area was likely already damaged causing an intermittent open circuit (see picture below):
https://drive.google.com/file/d/1rWMlrwLfhbJNxhbfClCU2yKun9rqh1ox/view?usp=sharing

Repair options I am contemplating are:
1. replace all items in the yellow box shown in the picture below:
https://drive.google.com/file/d/1fLfoaEdpz2zbsLk1dPEMG9bOA6gJ9Hjx/view?usp=sharing
2. replace the entire bridge circuit with a ready made one like this:
https://drive.google.com/file/d/1Is9QOZB8vmVIki7rdYBs04mxY-FFsYnz/view?usp=sharing

In case of option 1 suggestions on how to repair the damaged pad area and blown capacitor will be helpful.

In case of option 2 how can I connect the external bridge rectifier to the oven's control pcb (see the picture below), and what components have to be removed and what components remain to make the circuit function as was originally designed?
https://drive.google.com/file/d/1y4LFVXfZHLgJVGskIioYzmfbErOPy2Wu/view?usp=sharing

I am in the process of creating a drawing so that I can see what connects to what on the oven's pcb control board so that if repairing the current board I can solder the components correctly where the pads have been damaged. Any help or suggestion in this regard will be helpful. Once I have completed the drawing I will post a picture of it here.

Thank you for any suggestions and help.
 
I would leave D34 out of it's old location, that is a lost cause.
You can instead solder it on the top side of the board of the board.
D34 K to D40 A, D34 A to D33 A. K means cathode or the striped end, A means anode. So it would sit diagonal over top the other diodes and tack soldered to their leads. If the D34 leads are too short, then buy a replacement D34 as 1N4004 with new long leads.
Or get a bridge rectifier module like W04M and put that in place of the four diodes:
~AC to D40 A (T13), ~AC to D33 K or D39 A (T12), (+) to D40 K or D39 K pad, (-) to D33 A or D34 A pad (but that one's dead).

C29 did burn everything badly. I can't tell where it connected or quite how to add a thin jumper wire to replace the cooked traces.
C29 might be part of a voltage multiplier/zener D69 for the fluorescent display, assuming the appliance uses one. I did draw another Whirlpool/Maytag oven control board schematic I have to see if it's the same power supply circuit, usually it is.
 
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Thread Starter

bijancircuit

Joined Feb 21, 2021
67
prairiemystic thank you for your response.

"I can't tell where it connected or quite how to add a thin jumper wire to replace the cooked traces."
C29 arrangement on the board is as shown in the picture below:
https://drive.google.com/file/d/1rawZObjUHn5G0N9kYmwuZh74IBhJnbcn/view?usp=sharing

"C29 did burn everything badly."
Can an intermittent open circuit between C29 and D34A be the cause of the C29 to burnout?
Can you go into more details how a capacitor can get damaged in this way, what is its function etc?

I did get a ceramic capacitor and soldered it in place of C29 as shown in the picture below, but it did not fix the problem.
https://drive.google.com/file/d/1rawZObjUHn5G0N9kYmwuZh74IBhJnbcn/view?usp=sharing

I had taken C30 out of the board and measured its capacitance, it was 100nF. C30 and C29 should be the same value or 100nF. Unfortunately the replacement capacitor that was sent to me was of the wrong value and only 30nF, it was the seller's fault as I had specified the correct value. I realized this afterward I had installed the replacement capacitor on the board and the board still did not function. I then measure the capacitance value of the replacement capacitor and found that it was only 30nF.

Can a wrong value capacitor, in this case a 30nF instead of a 100nF cause the board to stop working or malfunction?

At the time of replacing the C29 with the wrong value 30nF ceramic capacitor I had not become aware that the connection between C29 and D34A was likely compromised, I only found that out when I had taken all 5 diodes out. Otherwise I would have run a small jumper from one terminal of C29 to D34A, I plan to do this at the next repair attempt.

I plan to made the following repair to the component side of the board as show in picture below (please note that the yellow indicates the reverse side of the board and red the component side):
https://drive.google.com/file/d/14H9IUYuVfTSsuLkNSSRaZmcEY9W4JkpG/view?usp=sharing

D39A pad does not look well either so I plan to solder it to both its pad and D33K.

I measured the value of the diodes and capacitors that were removed from the board and they are as follows:
D69 measures forward 0.500 and infinite reverse
D33 measures forward 0.520 and infinite reverse
D39 measures forward 0.509 and infinite reverse
D34 measures forward 0.508 and infinite reverse
D40 measures forward 0.482 and infinite reverse
Are any of these diode values out of line? I plan to reuse them so please let me know if they should not be reused and the reason. Thanks.

C34 rated 100μF measures 17 μF plan to replace with a 1800μF I have
D50 rated 100μF measures 54 nF plan to replace with a 1800μF I have

Both removed capacitors C34 and C50 seems to no longer hold their rated correct value, they also measure the same no matter how the meter lead are connected. I measured the new 1800μF capacitor that I have and the meter shows the correct rated value of the new capacitor and only if the leads of the meter are correctly attached to the capacitor. So the meter I am using is good and C34 and C50 are bad. Was this a contributing factor to the burned out? Was this caused by the burnt out? Are these capacitors the main cause of the intermittent operation of the oven?

I also measured the big C11 capacitor next to the rectifier section of the board. I did not remove C11 and measured it on the board. C11 is rated at 1000µF and measures 881 µF so pretty close. I know capacitors are not suppose to be measured on the board but I think this measurement is showing the true value of this capacitor even with the capacitor still attached to pcb.
 
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I think you had MLCC capacitor C29 fail and short. I have seen them do this when overvoltage hits them from mains transients, lightning damage. They need to be at least 100V parts because they are on the rectifiers for the 24VDC rail. Other parts being bad would not damage C29, C30.

I drew a schematic for the power supply section and confirm the two capacitors C29, C30 appear to be only for shunting electrical noise. So the controller should work with either of them out of circuit.
This means either the PCB traces are not fixed up quite right, or something else was a fuse. These ovens use a small power transformer which (secondary) goes to connector P16, and mains primary winding is pin 2, 3 "XFMR" on some other connector I can't see. The small transformer has a thermal fuse inside, it might have melted and check the primary winding is not open-circuit.

When a cap measures -20% in value, I take it as end of life. Although in-circuit or some multimeters don't read that accurately. For the time and money, I replace all electrolytic caps with top quality Nichicon, Chemi-con, Panasonic long-life parts. I see only five on the entire board. But maybe get the board to power up first.

Appliance control boards fail largely due to a few reasons:
1. Cold solder joints to connectors and relays, some cause fires and product recalls. Use a magnifier and inspect all high-current soldering and touch up as needed. T1, T5, T18 look not great.
2. The electrolytic capacitors age and dry out. Appliances usually have power on 24/7, so 8,760hrs a year. Worse if the part sees some local heat from nearby power resistors, the power transformer or the oven heat.
3. Relays go bad, the contacts wear out.
4. Power line surges
5. Cheap designs with planned obsolescense to make you buy a new oven.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
Thank you for your reply.
The main question I have is WHAT caused the intermittent operation of this oven. What part(s) failure is likely to blame for this?

I wanted to post the following pictures of the entire board so that you can see everything there:
https://drive.google.com/file/d/1wdMgwNZxcWQZyEVgxO-1TsES3hmcHQT6/view?usp=sharing
https://drive.google.com/file/d/1Ox9ZA7RyF97rTQBy10Styc8CjNVgCTbE/view?usp=sharing

These ovens use a small power transformer which (secondary) goes to connector P16, and mains primary winding is pin 2, 3 "XFMR" on some other connector I can't see. The small transformer has a thermal fuse inside, it might have melted and check the primary winding is not open-circuit.
Hopefully from the 2 pictures posted above you can now see the mains primary winding and point them out.
Of the plugs that go to the oven's control board there is one that has a thermal fuse. Is this the fuse for transformer that you are referring to in your post? This thermal fuse DOES have continuity (please see the picture below). I would imagine if it was a fuse problem it would not be intermittent, but please correct me if I am wrong. The intermittent nature of the problem suggest to me that perhaps the can type capacitors that don't measure at their correct value are perhaps the root cause of the problem. I remember once a computer that would not turn on intermittently and I found some bad capacitors on its motherboard. Replacing those bad electrolytic capacitors on that computer motherboard fixed it, at least for a while, before it stopped working permanently. I gave up on it so did not find what was the issue.
https://drive.google.com/file/d/1lKyaR0mBCjX3Iz0gF6wI5ELjKgMkV8Yx/view?usp=sharing

Here are some more pictures of what is on the other side of the oven's control board in case you need to point something out:
https://drive.google.com/file/d/1kDi17yIXpTMR5AGaPvNOGueh2-O984mg/view?usp=sharing
https://drive.google.com/file/d/1koiXvtdxbRCrG2gqxhUJmdEVdipv07pb/view?usp=sharing

For the time and money, I replace all electrolytic caps with top quality Nichicon, Chemi-con, Panasonic long-life parts. I see only five on the entire board. But maybe get the board to power up first.
What are the symptoms of electrolytic capacitors going bad? Would that make the board not function intermittently?
The pictures below show the replacement capacitors that I have so I will use them for now. I don't know what brand they are or if they are name brand high quality. I think they are probably Chinese no name brand I got from eBay. I checked the 3 brands you posted about and these are not any of them. I am posting the picture of the replacement capacitors below so that perhaps you can let me know their brand and their quality. Thanks.
https://drive.google.com/file/d/1VoYC_4aJj-r04wnJT-bwlfdBuT8vuima/view?usp=sharing
https://drive.google.com/file/d/1Q76lkYeR-NPsJkV1iP0egk4u8JHib6UU/view?usp=sharing

1. Cold solder joints to connectors and relays, some cause fires and product recalls. Use a magnifier and inspect all high-current soldering and touch up as needed. T1, T5, T18 look not great.
I will touch up T1, T5 and T18 once I start the repair. If you see anything else please let me know. Thanks.

2. The electrolytic capacitors age and dry out. Appliances usually have power on 24/7, so 8,760hrs a year. Worse if the part sees some local heat from nearby power resistors, the power transformer or the oven heat.
I did notice that the big resistors on the oven's control board have evidence of excess heat. Upon touching them I found them loose on the board. The pads for the resistors had lifted out of the board making them loose and wobbly (some of them not all), but I think the electrical connections are still OK. I did touch up the resistors' solder joints to the pcb and tried to "firm them up" with mixed success. If I put a little force on them they loosen again. The only way to fix this, as far as I can see, is to use some sort of glue to keep the resistor pads grip the board firmly I thought it is better to leave them rather that put some glue on them and then make it difficult or impossible to resolder at a later time if needed. Although I did watch a very good video on the internet of a guy who was restoring old Macintosh computers and he was using a sort of UV epoxy on the traces he would repair and then cure it with a UV lamp or under the sun. Here is the link to what he was using:
https://www.amazon.com/dp/B01MUB4PJ...colid=D9M6XM5Z554N&psc=1&ref_=lv_ov_lig_dp_it

4. Power line surges
What are the consequences of power line surges? I thought perhaps the capacitors going bad was one symptoms of power line surges.

5. Cheap designs with planned obsolescence to make you buy a new oven.
I am thinking about this quote right now and what comes to me is that probably the companies that design inferior stuff just don't know any better. They are probably not that good or clever to intentionally plan for obsolescence. In other words they don't do it intentionally. It is possible that due to low funds they use inferior parts and then if they are rewarded, like repeat customers after a part fails then they will continue to use the same inferior parts, otherwise they go out of business or are forced to change their ways.

Thank you for your help.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I think you had MLCC capacitor C29 fail and short. I have seen them do this when overvoltage hits them from mains transients, lightning damage. They need to be at least 100V parts because they are on the rectifiers for the 24VDC rail. Other parts being bad would not damage C29, C30.

I drew a schematic for the power supply section and confirm the two capacitors C29, C30 appear to be only for shunting electrical noise. So the controller should work with either of them out of circuit.
I am having difficulty finding a replacement for C29. What happens if I leave it out? Would that interfere with internet? Would the noise generated be harmful or annoying to humans? Can you direct me to a few reasonably priced substitute for C29?

Thanks.
 

wayneh

Joined Sep 9, 2010
17,152
What are the symptoms of electrolytic capacitors going bad? Would that make the board not function intermittently?
Yes, failure of electrolytic capacitors is probably the main cause of PCB failures. It's especially likely where the capacitor carries a high ripple current, for instance in the typical SMPS. Everyone of those that I've ever opened up, because it failed, had failed due to electrolytic caps. I've seen it in monitors, laptop PSUs, thermoelectric refrigerators, and more.

Years ago I read wise words here from the pros on PCB repair. They often advised shotgun replacement of electrolytic caps. Don't bother testing or fiddling, just replace them. I used to think that was silly, a waste of money if the board cannot be repaired. I am now on their side and endorse the "replace them all" approach. If you're successful, and you may well be, then your board has nice new caps. Like fresh tires on an old car.

EL caps fail first on ESR, the internal resistance. (You can measure this with the right meter, even in-circuit, but it's cheaper and more certain to just replace them.) In some circuits this is not fatal and you may coast through the ESR failure. It's critical in other circuits and will bring them down despite no loss of capacitance. Once a capacitor loses capacitance, it's beyond failed.

Note that not all EL caps are the same even if they have the same ratings for capacitance, voltage and physical dimensions. There is also a difference in ESR and some capacitors will be rated for "low ESR" or "high ripple current" or other terms. It can be tricky to sort out because they use different metrics. There are also ratings for temperature and lifetime. If you have a demanding application, you want better ratings to avoid another failure. No surprise, they'll cost more.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
wayneh thank you for your input good information to know about.

I should invest in some good quality electrolytic capacitor assortment for future. If you know of one on eBay or some other internet outlet I appreciate if you post a link.

Also I would like to post pictures to the site or some place where it would stay put for future reference, rather than Google Drive where I might eventually have to delete them due to limitation of storage space. I have had difficulty posting picture to forums such as this because the pictures I want to load are always too big and the site won't allow it. I don't know how to reduce their size. Any help in this department for future would be appreciate.
 

wayneh

Joined Sep 9, 2010
17,152
The pcb was repaired. C29 is left out for now. Before I install it back in the oven I like you to look at the following pictures and let me know if you see any issues. I appreciate it. Thank you.
https://drive.google.com/file/d/1V1570T-zprgK-ieuhLNtL33IHp1Ern3o/view?usp=sharing
https://drive.google.com/file/d/1-8u-UQ7bFpBVMpGhqkVF7R8KFVbKALc6/view?usp=sharing
Looks OK from my armchair view. I might be tempted to put a drop of hot glue on that wire jumper to hold it firmly in place and keep it from snagging on something during installation.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I just remembered something regarding failed capacitors, I read it on Wikipedia:
"The capacitor plague was a problem related to a higher-than-expected failure rate of non-solid aluminium electrolytic capacitors, between 1999 and 2007, especially those from some Taiwanese manufacturers, due to faulty electrolyte composition that caused corrosion accompanied by gas generation, often rupturing the case of the capacitor from the buildup of pressure.​
High failure rates occurred in many well-known brands of electronics, and were particularly evident in motherboards, video cards, and power supplies of personal computers."​
The following link is the entire article:
https://en.wikipedia.org/wiki/Capacitor_plague

1999 to 2007 is a huge time span and so it is likely that these capacitor failures will be observed for a lot longer time (maybe another 20 years before most old devices using them are retired), but are you still seeing failed capacitors past 2007? Of course to know this you need to know the date of manufacture of the capacitor or at least the device that has the capacitor and perhaps anything past 2007 is too new to tell.

In any case I thought I throw this out there just to share the article and that gun shutting the capacitors in devices made after 2007 may not be necessary.
 

wayneh

Joined Sep 9, 2010
17,152
I should invest in some good quality electrolytic capacitor assortment for future. If you know of one on eBay or some other internet outlet I appreciate if you post a link.
I'd be leery of eBay - too many counterfeits. You can say the same about Amazon but my last order of capacitors was from Amazon - I couldn't resist the price. Note that I stuck to a premium brand, in this case Panasonic.
https://www.amazon.com/gp/product/B073YQB9X2

The reliable supply houses are Mouser, DigiKey and Newark. I prefer the search tools at Mouser.
 

wayneh

Joined Sep 9, 2010
17,152
In any case I thought I throw this out there just to share the article and that gun shutting the capacitors in devices made after 2007 may not be necessary.
That day may come but the things I run into all have failed caps. It's a statistical probability thing: devices with bad caps self-segregate themselves for repair. I never see the devices that have good caps and are still working.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I just put the board back into the oven and turned the breakers on. Nothing. Black screen. Before when the oven door was opened the interior lights would come on, but now that does not happen either.
What should I do next?
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I plugged the board back in and push the breakers harder this time. Came back and now the upper oven lights do come on as the door is opened but not the lower oven's. Something like this happened the last time I put the board back in a few days ago, I thought I had not turned on the breakers properly but perhaps there is some issue either with breakers or the oven's door switch or something else.

At any rate now the interior lights of the oven do come on with the oven door opened so power is there.

I described the control board's behavior when installed in the picture below:
https://drive.google.com/file/d/17jDO7ez82XgKdi4MwKKzorAqyyKc1Qi0/view?usp=sharing

The control board is still black but I heard a sound so I started pushing the buttons on the control board and some of them do make the buzzer come.

In the following video you can hear the beep sound of the control board buttons and the 3 beep sound made when the START button is pushed. I am not sure but the 3 beep sound may indicate a code.
https://drive.google.com/file/d/1EcP4bSNUmUlkCvugsI2tj2iHEP5yzEgv/view?usp=sharing

I check the ribbon cable to the control board and it seems to be in all the way and firmly attached but I am still not 100% sure. But I tried to verify the ribbon is tucked in and attached well a few times and looks good to me.

What could be causing the black screen?
What could be causing no sound from Lower Oven Off button? And no interior lights in the lower oven?

Thank you.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I rechecked for lower oven lights and noticed that they do come on when the upper oven door is open. I think this is a design feature and the lower oven lights come on with then light button and when the upper oven door is opened and that is how they work right now. So I think there is no issue with the lights.
The main issue seems to be the blank screen and the oven not working which are probably related.
 

Thread Starter

bijancircuit

Joined Feb 21, 2021
67
I took the ribbon cable out again and put some Deoxit and put it back in but still black display. Something else is wrong I think.

The thought came to me that the missing C29 capacitor maybe causing this but then I reasoned the board would come on intermittently when C29 was not there, so this can't be the cause.

I plan to take close up pictures of the board and post them here in case someone sees something.
 
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Um, those new capacitors C34, C50 are typically used in older PC motherboards 1,800uF 6.3V and I can't see them being the right values for this oven controller. Especially the voltage rating. So I would expect the caps to heat up and pop.
Confirm the old part values, I know the circuit is over 6.3VDC
 
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